tatara_process/

boundary.rs

//! Boundary conditions — predicates that gate phase transitions.

use schemars::JsonSchema;
use serde::{Deserialize, Serialize};

use crate::flux_resource::FluxResource;

/// Boundary specification — preconditions gate Running,
/// postconditions gate Running → Attested.
#[derive(Clone, Debug, Default, Serialize, Deserialize, JsonSchema)]
#[serde(rename_all = "camelCase")]
pub struct Boundary {
    #[serde(default)]
    pub preconditions: Vec<Condition>,
    #[serde(default)]
    pub postconditions: Vec<Condition>,
    /// Max time before VERIFY fails — parsed as a `go`-style duration.
    /// Empty = controller default (15m).
    #[serde(default, skip_serializing_if = "Option::is_none")]
    pub timeout: Option<String>,
}

impl Boundary {
    /// True iff at least one [`Condition`] in
    /// `preconditions ∪ postconditions` carries the given
    /// [`ConditionKind`] — the ONE substrate primitive that owns the
    /// (closed-set discriminator, boundary-condition presence) probe on
    /// this typed surface.
    ///
    /// # Semantics
    ///
    /// The two condition vectors are unioned: a caller asking "does this
    /// spec name a `ClosedLoopAuth` predicate anywhere" doesn't care
    /// whether the operator authored it on the pre- or post-condition
    /// side. A boundary with the given kind on ONLY preconditions returns
    /// `true`; a boundary with the given kind on ONLY postconditions
    /// returns `true`; a boundary with neither returns `false`.
    ///
    /// # Sibling to [`crate::intent::Intent::has`] + [`crate::lifetime::Lifetime::has`]
    ///
    /// Same shape, same axis, third instance in the workspace-wide
    /// closed-set-driven presence-probe algebra. `Intent::has` +
    /// `Lifetime::has` publish the same `(&self, K) -> bool` signature
    /// where `K` is the discriminator's `Kind` (auto-derived through
    /// `#[derive(DeriveClosedSet)]`). A future normalization at that
    /// probe shape (a widened return carrying the matching Condition
    /// ref, a debug-build assertion on pre/post drift, a fleet-wide
    /// warn on redundant duplicates) lands at ONE site per surface
    /// and every downstream `<xxx>-<kind>` require-tag family +
    /// closed-set audit dispatcher picks it up mechanically.
    ///
    /// # Peer on the ephemeral surface — [`crate::ephemeral::EphemeralSpec::has_condition_kind`]
    ///
    /// Same signature `(ConditionKind) -> bool`, same union body
    /// (`preconditions.has_kind(k) || postconditions.has_kind(k)`), on
    /// the sugar-surface type [`crate::ephemeral::EphemeralSpec`] whose
    /// pre/post condition vectors live directly on the struct rather
    /// than inside a nested [`Boundary`] slot. Both methods compose
    /// against the ONE slice-level substrate primitive
    /// [`ConditionSliceExt::has_kind`] — a regression at the per-slice
    /// walk fails at that primitive's tests rather than as silent drift
    /// at either struct-level union caller. The ephemeral require-tag
    /// classifier reaches its `condition-<kind>` prefix family through
    /// the peer method byte-for-byte symmetrical with the point
    /// surface's `condition-<kind>` family that composes through this
    /// method.
    ///
    /// # Compounding
    ///
    /// The point-domain require-tag surface in
    /// `tatara-reconciler::bin::tatara-check` composes this primitive
    /// with the closed-set `FromStr` autoderived on [`ConditionKind`]
    /// through the `strip_and_classify_prefixed_kind` substrate to
    /// publish a `condition-<kind>` prefix family byte-for-byte
    /// symmetrical with `intent-<kind>` + `lifetime-<kind>`. A future
    /// [`ConditionKind`] variant added to `ALL` reaches every downstream
    /// (require-tag classifier, coherence check, editor completion
    /// provider) through the SAME closed-set walk with no per-caller
    /// edit.
    ///
    /// Theory anchor: THEORY.md §II.1 invariant 5 (composition preserves
    /// proofs — the presence-probe body lives at ONE substrate site so
    /// every downstream `condition-<kind>` requires-tag surface,
    /// closed-set audit dispatcher, and future variant addition binds
    /// through the SAME shape). THEORY.md §VI.1 (generation over
    /// composition — a ninth [`ConditionKind`] variant lands at ONE
    /// `ALL` entry + ONE `as_str` arm and the presence probe picks it
    /// up mechanically without further per-consumer edits).
    #[must_use]
    pub fn has_condition_kind(&self, kind: ConditionKind) -> bool {
        self.has_precondition_kind(kind) || self.has_postcondition_kind(kind)
    }

    /// True iff at least one [`Condition`] in `self.preconditions`
    /// carries the given [`ConditionKind`] — the precondition-side arm
    /// of the (precondition, postcondition, condition-union) triad on
    /// [`Boundary`], sibling to [`Self::has_postcondition_kind`] and
    /// half-composition of [`Self::has_condition_kind`].
    ///
    /// Thin typed delegate to [`ConditionSliceExt::has_kind`] over
    /// [`Self::preconditions`]. Peer of [`Self::has_postcondition_kind`]
    /// on the (precondition, postcondition) partition of the boundary's
    /// two condition-vector slots; both peers compose against the SAME
    /// slice-level substrate primitive and their `||` composition is
    /// [`Self::has_condition_kind`]. A regression that swapped the
    /// slice at either arm (a copy-paste that pointed the precondition
    /// probe at `self.postconditions`, an inline `.iter().any` closure
    /// body that outlasted the lift) surfaces at the composition-law
    /// pin `boundary_has_condition_kind_composes_precondition_and_postcondition_arms`
    /// rather than as silent classifier drift at every downstream
    /// `precondition-<kind>` require-tag callsite.
    ///
    /// # Why lift
    ///
    /// Pre-lift the point-domain `precondition-<kind>` require-tag
    /// classifier in `tatara-reconciler::bin::tatara-check` reached the
    /// precondition-side slice through direct field access
    /// (`spec.boundary.preconditions.has_kind(k)`) while its sibling
    /// `condition-<kind>` classifier routed through the named
    /// [`Self::has_condition_kind`] primitive. The asymmetry meant a
    /// future normalization at the presence-probe shape (a widened
    /// return carrying the matching [`Condition`] ref, a debug-build
    /// assertion on redundant duplicates, a fleet-wide warn on
    /// pre-only ClosedLoopAuth authoring) would land at the union
    /// primitive but bypass the two half-slice classifiers. Post-lift
    /// the (precondition, postcondition, condition-union) triad lives
    /// at ONE typed algebra surface on [`Boundary`], with the
    /// `condition-<K> = precondition-<K> ∨ postcondition-<K>`
    /// composition law pinned as a first-class typed invariant
    /// (see the composition-pin test in this module) rather than a
    /// per-caller discipline.
    ///
    /// # Semantics
    ///
    /// Returns `true` iff `self.preconditions.iter().any(|c| c.kind ==
    /// kind)`. Ignores `self.postconditions` — an operator who authored
    /// the kind on ONLY postconditions gets `false` from this probe and
    /// `true` from [`Self::has_postcondition_kind`]. The two half-slice
    /// arms partition the (kind, side) matrix exhaustively across the
    /// four states (kind absent both, pre-only, post-only, both).
    ///
    /// # Sibling to [`crate::ephemeral::EphemeralSpec::has_precondition_kind`]
    ///
    /// Same shape, same axis, third and fourth methods in the
    /// workspace-wide `has_(pre|post)condition_kind` two-surface
    /// family. [`crate::ephemeral::EphemeralSpec::has_precondition_kind`]
    /// composes byte-identical `preconditions.has_kind(k)` semantics on
    /// the sugar-surface type's direct `preconditions: Vec<Condition>`
    /// field, so both surfaces publish a `precondition-<kind>` require-
    /// tag prefix family byte-for-byte symmetrical (point surface
    /// through this method, ephemeral surface through its peer).
    ///
    /// Theory anchor: THEORY.md §II.1 invariant 5 (composition
    /// preserves proofs — the per-slice presence-probe body lives at
    /// ONE substrate site so every downstream `precondition-<kind>`
    /// require-tag surface, closed-set audit dispatcher, and future
    /// variant addition binds through the SAME shape). THEORY.md §VI.1
    /// (generation over composition — the union primitive
    /// [`Self::has_condition_kind`] emerges from the composition of
    /// its two half-slice arms rather than as a hand-authored `||`
    /// closure at every downstream consumer).
    #[must_use]
    pub fn has_precondition_kind(&self, kind: ConditionKind) -> bool {
        self.preconditions.has_kind(kind)
    }

    /// True iff at least one [`Condition`] in `self.postconditions`
    /// carries the given [`ConditionKind`] — the postcondition-side arm
    /// of the (precondition, postcondition, condition-union) triad on
    /// [`Boundary`], sibling to [`Self::has_precondition_kind`] and
    /// half-composition of [`Self::has_condition_kind`].
    ///
    /// Thin typed delegate to [`ConditionSliceExt::has_kind`] over
    /// [`Self::postconditions`]. Peer of [`Self::has_precondition_kind`]
    /// on the (precondition, postcondition) partition of the boundary's
    /// two condition-vector slots. See [`Self::has_precondition_kind`]
    /// for the full rationale — the two methods share ONE lift
    /// motivation, ONE fail-before-pass-after composition-law pin, and
    /// ONE two-surface parity contract with the ephemeral sugar type
    /// via [`crate::ephemeral::EphemeralSpec::has_postcondition_kind`].
    #[must_use]
    pub fn has_postcondition_kind(&self, kind: ConditionKind) -> bool {
        self.postconditions.has_kind(kind)
    }

    /// Returns the first [`Condition`] in
    /// `preconditions ∪ postconditions` carrying the given
    /// [`ConditionKind`], searching preconditions first — the
    /// widened peer of [`Self::has_condition_kind`] one refinement
    /// higher on the presence-probe algebra.
    ///
    /// # Sibling to [`Self::has_condition_kind`]
    ///
    /// Same axis, one refinement wider: `has_condition_kind` collapses
    /// the return to a `bool` (`find_condition_kind(k).is_some()`);
    /// this method returns the matching `&Condition` so consumers can
    /// read [`Condition::params`] (the `probeImage`, the `expression`,
    /// the `flakeRef`) at the presence probe's own callsite without
    /// re-walking the two condition vectors. Pinned by the composition
    /// law `has_condition_kind(K) == find_condition_kind(K).is_some()`
    /// at [`Boundary`]'s substrate-delegation test.
    ///
    /// # Semantics — precondition takes precedence
    ///
    /// Walks [`Self::preconditions`] first, then [`Self::postconditions`]:
    /// a kind authored on BOTH sides returns the precondition-side
    /// [`Condition`]. Callers that need the postcondition-side match
    /// specifically reach for [`Self::find_postcondition_kind`]; callers
    /// that need every match across both sides walk the two vectors
    /// directly. Composition law: `find_condition_kind(K) ==
    /// find_precondition_kind(K).or_else(|| find_postcondition_kind(K))`,
    /// pinned as a first-class typed invariant.
    ///
    /// # Peer on the ephemeral surface — [`crate::ephemeral::EphemeralSpec::find_condition_kind`]
    ///
    /// Same signature `(ConditionKind) -> Option<&Condition>`, same
    /// precondition-first body, on the sugar-surface type whose
    /// pre/post condition vectors live directly on the struct. Both
    /// methods compose against the SAME slice-level substrate primitive
    /// [`ConditionSliceExt::find_kind`] — a regression at the per-slice
    /// walk fails at that primitive's tests rather than as silent drift
    /// at either struct-level widened caller.
    ///
    /// # Compounding
    ///
    /// A future diagnostic consumer (an operator-facing "condition
    /// {kind} matched on {side} with params.{key}={value}" message
    /// emitted by the require-tag classifier, a coherence check that
    /// verifies "every `ClosedLoopAuth` postcondition carries a
    /// non-empty `probeImage`" by inspecting the returned
    /// `&Condition.params`, an editor completion listing which
    /// params-keys appear on the present kind) reaches for the
    /// matching [`Condition`] through this ONE method rather than
    /// re-walking the two vectors with `iter().find(...)` at the
    /// callsite. The presence-probe axis now carries both refinements
    /// (bool via `has_condition_kind`, `&Condition` via
    /// `find_condition_kind`) at ONE typed algebra surface per struct.
    ///
    /// Theory anchor: THEORY.md §II.1 invariant 5 (composition
    /// preserves proofs — the widened return lives at ONE substrate
    /// site so every downstream diagnostic consumer + coherence check
    /// binds through the SAME shape rather than restating the
    /// `.iter().find(|c| c.kind == K)` closure body).
    #[must_use]
    pub fn find_condition_kind(&self, kind: ConditionKind) -> Option<&Condition> {
        self.find_precondition_kind(kind)
            .or_else(|| self.find_postcondition_kind(kind))
    }

    /// Returns the first [`Condition`] in [`Self::preconditions`]
    /// carrying the given [`ConditionKind`], or `None` — the
    /// precondition-side arm of the (precondition, postcondition,
    /// condition-union) widened triad on [`Boundary`]. Thin typed
    /// delegate to [`ConditionSliceExt::find_kind`] over
    /// [`Self::preconditions`].
    ///
    /// Peer of [`Self::find_postcondition_kind`] on the (precondition,
    /// postcondition) partition of the boundary's two condition-vector
    /// slots; both peers compose against the SAME slice-level substrate
    /// primitive and their `or_else` composition is
    /// [`Self::find_condition_kind`]. Byte-identical semantics to
    /// [`Self::has_precondition_kind`] with a widened `Option<&Condition>`
    /// return rather than a `bool`.
    #[must_use]
    pub fn find_precondition_kind(&self, kind: ConditionKind) -> Option<&Condition> {
        self.preconditions.find_kind(kind)
    }

    /// Returns the first [`Condition`] in [`Self::postconditions`]
    /// carrying the given [`ConditionKind`], or `None` — the
    /// postcondition-side arm of the (precondition, postcondition,
    /// condition-union) widened triad on [`Boundary`]. Thin typed
    /// delegate to [`ConditionSliceExt::find_kind`] over
    /// [`Self::postconditions`].
    ///
    /// Peer of [`Self::find_precondition_kind`] on the (precondition,
    /// postcondition) partition of the boundary's two condition-vector
    /// slots. See [`Self::find_precondition_kind`] for the full
    /// rationale — the two methods share ONE lift motivation, ONE
    /// fail-before-pass-after composition-law pin, and ONE two-surface
    /// parity contract with the ephemeral sugar type via
    /// [`crate::ephemeral::EphemeralSpec::find_postcondition_kind`].
    #[must_use]
    pub fn find_postcondition_kind(&self, kind: ConditionKind) -> Option<&Condition> {
        self.postconditions.find_kind(kind)
    }

    /// Returns an iterator over every [`Condition`] in
    /// `preconditions ∪ postconditions` carrying the given
    /// [`ConditionKind`], walking preconditions first — the
    /// widened peer of [`Self::find_condition_kind`] one refinement
    /// higher on the presence-probe algebra. Byte-for-byte
    /// equivalent to
    /// `self.iter_precondition_kind(kind).chain(self.iter_postcondition_kind(kind))`.
    ///
    /// # Sibling to [`Self::find_condition_kind`]
    ///
    /// Same axis, one refinement wider: `find_condition_kind`
    /// collapses the return to the FIRST match (yielding
    /// `Option<&Condition>`); this method yields every match across
    /// both sides. Pinned by the composition law
    /// `find_condition_kind(K) == iter_condition_kind(K).next()` at
    /// [`Boundary`]'s substrate-delegation test — the two refinements
    /// share ONE walk order by construction (preconditions first,
    /// then postconditions), so a regression that reversed the
    /// [`Chain`](std::iter::Chain) order or narrowed the union to an
    /// intersection surfaces HERE at the substrate boundary rather
    /// than as silent skew between the first-match and stream
    /// refinements downstream consumers reach through.
    ///
    /// # Peer on the ephemeral surface — [`crate::ephemeral::EphemeralSpec::iter_condition_kind`]
    ///
    /// Same signature `(ConditionKind) -> Chain<KindMatches<'_>,
    /// KindMatches<'_>>`, same precondition-first chain body, on the
    /// sugar-surface type whose pre/post condition vectors live
    /// directly on the struct. Both methods compose against the SAME
    /// slice-level substrate primitive [`ConditionSliceExt::iter_kind`]
    /// — a regression at the per-slice walk fails at that primitive's
    /// tests rather than as silent drift at either struct-level
    /// widened caller.
    ///
    /// # Compounding
    ///
    /// A future coherence check that enforces "each
    /// [`ConditionKind`] appears at most once across
    /// preconditions ∪ postconditions" reads
    /// `boundary.iter_condition_kind(k).nth(1).is_none()` at ONE
    /// call site rather than restating the count-with-filter closure
    /// body over the two vector slots. A future diagnostic
    /// enumerating every match (an operator-facing "N ClosedLoopAuth
    /// conditions matched, listing sides + params" message emitted
    /// by the require-tag classifier) reaches this ONE method
    /// through `boundary.iter_condition_kind(k).collect()` rather
    /// than chaining two half-slice walks at the callsite.
    /// The presence-probe axis on [`Boundary`] now carries three
    /// refinements (bool via `has_condition_kind`,
    /// `Option<&Condition>` via `find_condition_kind`,
    /// `impl Iterator<Item = &Condition>` via
    /// `iter_condition_kind`) at ONE typed algebra surface, byte-
    /// for-byte peer of the same triad on
    /// [`crate::ephemeral::EphemeralSpec`].
    ///
    /// Theory anchor: THEORY.md §II.1 invariant 5 (composition
    /// preserves proofs — the widened stream lives at ONE substrate
    /// site so every downstream diagnostic + coherence consumer binds
    /// through the SAME shape rather than restating the two-half
    /// chain body).
    pub fn iter_condition_kind(
        &self,
        kind: ConditionKind,
    ) -> std::iter::Chain<KindMatches<'_>, KindMatches<'_>> {
        self.iter_precondition_kind(kind)
            .chain(self.iter_postcondition_kind(kind))
    }

    /// Returns an iterator over every [`Condition`] in
    /// [`Self::preconditions`] carrying the given [`ConditionKind`]
    /// — the precondition-side arm of the (precondition,
    /// postcondition, condition-union) iterator triad on
    /// [`Boundary`]. Thin typed delegate to
    /// [`ConditionSliceExt::iter_kind`] over [`Self::preconditions`].
    ///
    /// Peer of [`Self::iter_postcondition_kind`] on the (precondition,
    /// postcondition) partition of the boundary's two condition-vector
    /// slots; both peers compose against the SAME slice-level substrate
    /// primitive and their [`Chain`](std::iter::Chain) composition is
    /// [`Self::iter_condition_kind`]. Byte-identical semantics to
    /// [`Self::find_precondition_kind`] with a widened stream return
    /// rather than only the first match.
    pub fn iter_precondition_kind(&self, kind: ConditionKind) -> KindMatches<'_> {
        self.preconditions.iter_kind(kind)
    }

    /// Returns an iterator over every [`Condition`] in
    /// [`Self::postconditions`] carrying the given [`ConditionKind`]
    /// — the postcondition-side arm of the (precondition,
    /// postcondition, condition-union) iterator triad on
    /// [`Boundary`]. Thin typed delegate to
    /// [`ConditionSliceExt::iter_kind`] over
    /// [`Self::postconditions`].
    ///
    /// Peer of [`Self::iter_precondition_kind`] on the (precondition,
    /// postcondition) partition of the boundary's two condition-vector
    /// slots. See [`Self::iter_precondition_kind`] for the full
    /// rationale — the two methods share ONE lift motivation, ONE
    /// fail-before-pass-after composition-law pin, and ONE
    /// two-surface parity contract with the ephemeral sugar type via
    /// [`crate::ephemeral::EphemeralSpec::iter_postcondition_kind`].
    pub fn iter_postcondition_kind(&self, kind: ConditionKind) -> KindMatches<'_> {
        self.postconditions.iter_kind(kind)
    }

    /// Number of [`Condition`]s in `preconditions ∪ postconditions`
    /// carrying the given [`ConditionKind`] — the scalar cardinality
    /// arm of the (precondition, postcondition, condition-union)
    /// count triad on [`Boundary`]. Composed as
    /// `count_precondition_kind(k) + count_postcondition_kind(k)` —
    /// the ONE SUM-composed arm on the presence-probe algebra
    /// (distinct from `has_condition_kind`'s `||` union,
    /// `find_condition_kind`'s `or_else` first-match, and
    /// `iter_condition_kind`'s `Chain` stream).
    ///
    /// # Sibling to [`Self::iter_condition_kind`]
    ///
    /// Same axis, one refinement lower on the cardinality projection:
    /// `iter_condition_kind` yields the whole match stream across both
    /// sides; this method collapses that stream to its cardinality
    /// without materializing any intermediate [`Vec`]. Composition law
    /// `count_condition_kind(K) == iter_condition_kind(K).count()`
    /// pinned as a first-class typed invariant at the substrate-
    /// delegation test.
    ///
    /// # Peer on the ephemeral surface — [`crate::ephemeral::EphemeralSpec::count_condition_kind`]
    ///
    /// Same signature `(ConditionKind) -> usize`, same SUM body, on
    /// the sugar-surface type whose pre/post condition vectors live
    /// directly on the struct. Both methods compose against the SAME
    /// slice-level substrate primitive [`ConditionSliceExt::count_kind`]
    /// — a regression at the per-slice count fails at that primitive's
    /// tests rather than as silent drift at either struct-level union
    /// caller.
    ///
    /// # Compounding
    ///
    /// A future coherence check that enforces "each [`ConditionKind`]
    /// appears at most once across preconditions ∪ postconditions"
    /// reads `boundary.count_condition_kind(k) <= 1` at ONE call site.
    /// A future require-tag classifier arm that surfaces multiplicity
    /// to the operator (a hypothetical `condition-count-<kind>` prefix
    /// family, an audit dump reporting "N ClosedLoopAuth conditions
    /// matched") reaches this ONE method rather than restating the
    /// `.iter_condition_kind(k).count()` chain body at the callsite.
    /// The presence-probe axis on [`Boundary`] now carries FOUR
    /// refinements (bool via `has_condition_kind`, `Option<&Condition>`
    /// via `find_condition_kind`, `impl Iterator<Item = &Condition>`
    /// via `iter_condition_kind`, `usize` via `count_condition_kind`)
    /// at ONE typed algebra surface per struct, byte-for-byte peer of
    /// the same tetrad on [`crate::ephemeral::EphemeralSpec`].
    ///
    /// Theory anchor: THEORY.md §II.1 invariant 5 (composition
    /// preserves proofs — the scalar cardinality lives at ONE
    /// substrate site so every downstream diagnostic + coherence
    /// consumer binds through the SAME shape rather than restating
    /// the two-half sum body).
    #[must_use]
    pub fn count_condition_kind(&self, kind: ConditionKind) -> usize {
        self.count_precondition_kind(kind) + self.count_postcondition_kind(kind)
    }

    /// Number of [`Condition`]s in [`Self::preconditions`] carrying
    /// the given [`ConditionKind`] — the precondition-side arm of the
    /// (precondition, postcondition, condition-union) count triad on
    /// [`Boundary`]. Thin typed delegate to
    /// [`ConditionSliceExt::count_kind`] over [`Self::preconditions`].
    ///
    /// Peer of [`Self::count_postcondition_kind`] on the (precondition,
    /// postcondition) partition of the boundary's two condition-vector
    /// slots; both peers compose against the SAME slice-level substrate
    /// primitive and their `+` composition is
    /// [`Self::count_condition_kind`]. Byte-identical semantics to
    /// [`Self::iter_precondition_kind`] with the scalar `usize`
    /// cardinality projection rather than the widened stream.
    #[must_use]
    pub fn count_precondition_kind(&self, kind: ConditionKind) -> usize {
        self.preconditions.count_kind(kind)
    }

    /// Number of [`Condition`]s in [`Self::postconditions`] carrying
    /// the given [`ConditionKind`] — the postcondition-side arm of
    /// the (precondition, postcondition, condition-union) count triad
    /// on [`Boundary`]. Thin typed delegate to
    /// [`ConditionSliceExt::count_kind`] over
    /// [`Self::postconditions`].
    ///
    /// Peer of [`Self::count_precondition_kind`]. See that method for
    /// the full rationale — the two methods share ONE lift motivation,
    /// ONE fail-before-pass-after composition-law pin, and ONE
    /// two-surface parity contract with the ephemeral sugar type via
    /// [`crate::ephemeral::EphemeralSpec::count_postcondition_kind`].
    #[must_use]
    pub fn count_postcondition_kind(&self, kind: ConditionKind) -> usize {
        self.postconditions.count_kind(kind)
    }

    /// The set of [`ConditionKind`] variants that appear at least once in
    /// `preconditions ∪ postconditions`, projected in
    /// [`ConditionKind::ALL`] order — the closed-set-inversion refinement
    /// on the presence-probe algebra (distinct axis from the four point-
    /// probe refinements: bool via [`Self::has_condition_kind`],
    /// `Option<&Condition>` via [`Self::find_condition_kind`],
    /// `impl Iterator<Item = &Condition>` via [`Self::iter_condition_kind`],
    /// `usize` via [`Self::count_condition_kind`]).
    ///
    /// # Composed body
    ///
    /// `ConditionKind::ALL.into_iter().filter(|k|
    /// self.has_condition_kind(*k)).collect()` — a thin projection over
    /// the closed set composed against the two-slice union primitive
    /// [`Self::has_condition_kind`]. Equivalent to the set-union of
    /// [`Self::distinct_precondition_kinds`] and
    /// [`Self::distinct_postcondition_kinds`] projected in canonical
    /// [`ConditionKind::ALL`] order (the union composition law pinned by
    /// the substrate testkit macro [`crate::assert_surface_union_composition_laws`]).
    ///
    /// # Peer on the ephemeral surface — [`crate::ephemeral::EphemeralSpec::distinct_condition_kinds`]
    ///
    /// Same signature `(&Self) -> Vec<ConditionKind>`, same closed-set-
    /// inversion body, on the sugar-surface type whose pre/post condition
    /// vectors live directly on the struct. Both methods compose against
    /// the SAME slice-level substrate primitive
    /// [`ConditionSliceExt::distinct_kinds`] via the two-slice union
    /// composed through [`Self::has_condition_kind`] — a regression at
    /// the per-slice walk fails at that primitive's tests rather than as
    /// silent drift at either struct-level union caller.
    ///
    /// # Sibling to the four point-probe refinements
    ///
    /// FIFTH refinement on the boundary-surface presence-probe algebra,
    /// distinct in axis from the other four: `has_condition_kind` /
    /// `find_condition_kind` / `iter_condition_kind` /
    /// `count_condition_kind` fix a [`ConditionKind`] and vary the return
    /// type; this refinement INVERTS the axis by fixing the boundary and
    /// varying over [`ConditionKind::ALL`]. The composition law
    /// `distinct_condition_kinds().contains(&k) == has_condition_kind(k)`
    /// for every `k ∈ ConditionKind::ALL` binds the closed-set-inversion
    /// probe to the point probe at the (precondition, postcondition,
    /// condition-union) triad.
    ///
    /// # Compounding
    ///
    /// A future coherence check that enforces "every process boundary
    /// carries at least ONE distinct kind" (a warning surfaced when
    /// `spec.boundary.distinct_condition_kinds().is_empty()`) reaches
    /// this ONE method rather than paying for the eight-way sweep with
    /// `has_condition_kind` at every callsite. A future require-tag
    /// classifier that surfaces the distinct-set cardinality as a scalar
    /// (a hypothetical `condition-kinds-distinct-<n>` prefix family, an
    /// audit dump reporting "boundary carries N distinct kinds") reaches
    /// this ONE method through `.distinct_condition_kinds().len()`
    /// rather than restating the closed-set-inverted filter idiom at
    /// every callsite.
    ///
    /// Theory anchor: THEORY.md §II.1 invariant 5 (composition preserves
    /// proofs — the closed-set-inversion aggregate is a typed projection
    /// of [`Self::has_condition_kind`] over [`ConditionKind::ALL`], and
    /// every downstream aggregate consumer binds through the SAME shape).
    /// THEORY.md §VI.1 (generation over composition — a new
    /// [`ConditionKind`] variant added to `ALL` reaches this method
    /// mechanically through the closed-set walk).
    #[must_use]
    pub fn distinct_condition_kinds(&self) -> Vec<ConditionKind> {
        ConditionKind::ALL
            .into_iter()
            .filter(|k| self.has_condition_kind(*k))
            .collect()
    }

    /// The set of [`ConditionKind`] variants appearing at least once in
    /// [`Self::preconditions`], projected in [`ConditionKind::ALL`]
    /// order — the precondition-side arm of the (precondition,
    /// postcondition, condition-union) distinct-set triad on
    /// [`Boundary`]. Thin typed delegate to
    /// [`ConditionSliceExt::distinct_kinds`] over
    /// [`Self::preconditions`].
    ///
    /// Peer of [`Self::distinct_postcondition_kinds`] on the
    /// (precondition, postcondition) partition of the boundary's two
    /// condition-vector slots; both peers compose against the SAME
    /// slice-level substrate primitive and their canonical set-union
    /// (projected in [`ConditionKind::ALL`] order) is
    /// [`Self::distinct_condition_kinds`].
    #[must_use]
    pub fn distinct_precondition_kinds(&self) -> Vec<ConditionKind> {
        self.preconditions.distinct_kinds()
    }

    /// The set of [`ConditionKind`] variants appearing at least once in
    /// [`Self::postconditions`], projected in [`ConditionKind::ALL`]
    /// order — the postcondition-side arm of the (precondition,
    /// postcondition, condition-union) distinct-set triad on
    /// [`Boundary`]. Thin typed delegate to
    /// [`ConditionSliceExt::distinct_kinds`] over
    /// [`Self::postconditions`].
    ///
    /// Peer of [`Self::distinct_precondition_kinds`]. See that method
    /// for the full rationale — the two methods share ONE lift
    /// motivation, ONE fail-before-pass-after composition-law pin, and
    /// ONE two-surface parity contract with the ephemeral sugar type
    /// via [`crate::ephemeral::EphemeralSpec::distinct_postcondition_kinds`].
    #[must_use]
    pub fn distinct_postcondition_kinds(&self) -> Vec<ConditionKind> {
        self.postconditions.distinct_kinds()
    }

    /// Zero-allocation iterator peer of [`Self::distinct_condition_kinds`]
    /// — the condition-union arm of the (precondition, postcondition,
    /// condition-union) closed-set-inversion iterator triad on
    /// [`Boundary`]. Walks [`ConditionKind::ALL`] in canonical order and
    /// yields every [`ConditionKind`] appearing at least once in
    /// `preconditions ∪ postconditions`, WITHOUT materializing an
    /// intermediate `Vec<ConditionKind>`.
    ///
    /// Composed body:
    /// `ConditionKind::ALL.iter().copied().filter(|&k|
    /// self.has_condition_kind(k))` — a thin projection over the closed
    /// set composed against the two-slice union primitive
    /// [`Self::has_condition_kind`], byte-identical to the trait-level
    /// [`ConditionSliceExt::iter_distinct_kinds`] but reaching through
    /// the boundary's two-slice union rather than a single slice.
    /// Equivalent to `self.distinct_condition_kinds().into_iter()` without
    /// the intermediate heap allocation.
    ///
    /// Peer on the ephemeral surface — [`crate::ephemeral::EphemeralSpec::iter_distinct_condition_kinds`].
    /// Sibling to the three-slice `iter_*_condition_kinds` triad —
    /// `iter_distinct_condition_kinds` walks the union, the two half-
    /// slice arms `iter_distinct_precondition_kinds` and
    /// `iter_distinct_postcondition_kinds` walk each side alone. See
    /// [`Self::distinct_condition_kinds`] for the full rationale on the
    /// closed-set-inversion aggregate.
    pub fn iter_distinct_condition_kinds(&self) -> impl Iterator<Item = ConditionKind> + '_ {
        ConditionKind::ALL
            .iter()
            .copied()
            .filter(|&k| self.has_condition_kind(k))
    }

    /// Zero-allocation iterator peer of
    /// [`Self::distinct_precondition_kinds`] — the precondition-side arm
    /// of the (precondition, postcondition, condition-union) closed-set-
    /// inversion iterator triad on [`Boundary`]. Thin typed delegate to
    /// [`ConditionSliceExt::iter_distinct_kinds`] over
    /// [`Self::preconditions`].
    pub fn iter_distinct_precondition_kinds(&self) -> impl Iterator<Item = ConditionKind> + '_ {
        self.preconditions.iter_distinct_kinds()
    }

    /// Zero-allocation iterator peer of
    /// [`Self::distinct_postcondition_kinds`] — the postcondition-side
    /// arm of the (precondition, postcondition, condition-union) closed-
    /// set-inversion iterator triad on [`Boundary`]. Thin typed delegate
    /// to [`ConditionSliceExt::iter_distinct_kinds`] over
    /// [`Self::postconditions`].
    pub fn iter_distinct_postcondition_kinds(&self) -> impl Iterator<Item = ConditionKind> + '_ {
        self.postconditions.iter_distinct_kinds()
    }

    /// Scalar cardinality of the [`ConditionKind`] set appearing at
    /// least once in `preconditions ∪ postconditions` — the
    /// condition-union arm of the (precondition, postcondition,
    /// condition-union) distinct-kind-count triad on [`Boundary`].
    ///
    /// # Composed body
    ///
    /// `ConditionKind::ALL.iter().filter(|k|
    /// self.has_condition_kind(**k)).count()` — a thin projection over
    /// the closed set composed against the two-slice union primitive
    /// [`Self::has_condition_kind`], byte-identical to the trait-level
    /// [`ConditionSliceExt::distinct_kind_count`] but reaching through
    /// the boundary's two-slice union rather than a single slice.
    /// Equivalent to `self.distinct_condition_kinds().len()` without
    /// materializing the intermediate `Vec<ConditionKind>`.
    ///
    /// # Sibling to [`Self::distinct_condition_kinds`]
    ///
    /// Scalar projection of the closed-set-inversion widened primitive
    /// on the boundary-union surface — where `distinct_condition_kinds`
    /// returns the SET, `distinct_condition_kind_count` collapses it to
    /// its cardinality. Byte-for-byte peer of the point-domain scalar
    /// projection [`ConditionSliceExt::distinct_kind_count`] one
    /// struct-layer down, and of the peer surface sugar
    /// [`crate::ephemeral::EphemeralSpec::distinct_condition_kind_count`]
    /// one struct-layer sideways.
    ///
    /// # Compounding
    ///
    /// A future coherence check that enforces "every process boundary
    /// carries at least ONE distinct kind" now reads
    /// `spec.boundary.distinct_condition_kind_count() > 0` at ONE call
    /// site rather than paying for
    /// `spec.boundary.distinct_condition_kinds().len() > 0` (with its
    /// intermediate heap allocation) or the eight-way `has_*_kind`
    /// sweep at the callsite. A future require-tag classifier arm that
    /// publishes the distinct-set cardinality as a scalar (a
    /// hypothetical `condition-kinds-distinct-<n>` prefix family)
    /// reaches this ONE primitive without allocating.
    ///
    /// Theory anchor: THEORY.md §II.1 invariant 5 — composition
    /// preserves proofs (the scalar cardinality composes the SAME
    /// closed-set walk on both this boundary surface and the
    /// slice-level substrate primitive). THEORY.md §VI.1 — generation
    /// over composition (a new [`ConditionKind`] variant added to
    /// `ALL` reaches this primitive mechanically through the closed-set
    /// walk).
    #[must_use]
    pub fn distinct_condition_kind_count(&self) -> usize {
        ConditionKind::ALL
            .iter()
            .filter(|k| self.has_condition_kind(**k))
            .count()
    }

    /// Scalar cardinality of the [`ConditionKind`] set appearing at
    /// least once in [`Self::preconditions`] — the precondition-side
    /// arm of the (precondition, postcondition, condition-union)
    /// distinct-kind-count triad on [`Boundary`]. Thin typed delegate
    /// to [`ConditionSliceExt::distinct_kind_count`] over
    /// [`Self::preconditions`].
    ///
    /// Peer of [`Self::distinct_postcondition_kind_count`] on the
    /// (precondition, postcondition) partition of the boundary's two
    /// condition-vector slots; both peers compose against the SAME
    /// slice-level substrate primitive so a regression at the per-slice
    /// closed-set walk fails at that primitive's tests rather than as
    /// silent drift at either struct-level scalar-cardinality arm.
    #[must_use]
    pub fn distinct_precondition_kind_count(&self) -> usize {
        self.preconditions.distinct_kind_count()
    }

    /// Scalar cardinality of the [`ConditionKind`] set appearing at
    /// least once in [`Self::postconditions`] — the postcondition-side
    /// arm of the (precondition, postcondition, condition-union)
    /// distinct-kind-count triad on [`Boundary`]. Thin typed delegate
    /// to [`ConditionSliceExt::distinct_kind_count`] over
    /// [`Self::postconditions`].
    ///
    /// Peer of [`Self::distinct_precondition_kind_count`]. See that
    /// method for the full rationale — the two methods share ONE lift
    /// motivation, ONE fail-before-pass-after composition-law pin, and
    /// ONE two-surface parity contract with the ephemeral sugar type
    /// via
    /// [`crate::ephemeral::EphemeralSpec::distinct_postcondition_kind_count`].
    #[must_use]
    pub fn distinct_postcondition_kind_count(&self) -> usize {
        self.postconditions.distinct_kind_count()
    }

    /// The set of [`ConditionKind`] variants that do NOT appear in
    /// `preconditions ∪ postconditions`, projected in
    /// [`ConditionKind::ALL`] order — the closed-set-inversion
    /// COMPLEMENT of [`Self::distinct_condition_kinds`] on the
    /// (precondition, postcondition, condition-union) missing-set triad.
    ///
    /// # Composed body
    ///
    /// `ConditionKind::ALL.into_iter().filter(|k|
    /// !self.has_condition_kind(*k)).collect()` — a thin projection
    /// over the closed set composed against the two-slice union
    /// primitive [`Self::has_condition_kind`] under a negated
    /// predicate. Equivalent to the SET-INTERSECTION of
    /// [`Self::missing_precondition_kinds`] and
    /// [`Self::missing_postcondition_kinds`] projected in canonical
    /// [`ConditionKind::ALL`] order — a kind is missing from the
    /// union iff it is missing from BOTH half-slices (the union-
    /// composition law pinned by the substrate testkit macro
    /// [`crate::assert_surface_union_composition_laws`]).
    ///
    /// # Peer on the ephemeral surface — [`crate::ephemeral::EphemeralSpec::missing_condition_kinds`]
    ///
    /// Same signature `(&Self) -> Vec<ConditionKind>`, same closed-set-
    /// complement body, on the sugar-surface type. Both methods compose
    /// against the SAME slice-level substrate primitive
    /// [`ConditionSliceExt::missing_kinds`] via the two-slice union
    /// composed through [`Self::has_condition_kind`] — a regression at
    /// the per-slice walk fails at that primitive's tests rather than
    /// as silent drift at either struct-level complement caller.
    ///
    /// # Sibling to [`Self::distinct_condition_kinds`]
    ///
    /// SIXTH refinement on the boundary-surface presence-probe algebra,
    /// on the SAME closed-set-inversion axis as `distinct_condition_kinds`
    /// but under a NEGATED point-probe. The composition law
    /// `missing_condition_kinds().contains(&k) ==
    /// !has_condition_kind(k)` for every `k ∈ ConditionKind::ALL`
    /// binds the complement to the point probe at the triad — and the
    /// two widened primitives PARTITION `ConditionKind::ALL` (their
    /// union covers `ALL`, their intersection is empty, their
    /// cardinalities sum to `ALL.len()`).
    ///
    /// # Compounding
    ///
    /// A future coherence check that enforces "every process boundary
    /// carries a [`ConditionKind::JobAttested`] postcondition" surfaces
    /// the operator-facing gap diagnostic
    /// `spec.boundary.postconditions.missing_kinds()` verbatim (naming
    /// EVERY kind absent from postconditions in canonical order). A
    /// future operator-facing "boundary is MISSING [JobAttested,
    /// ClosedLoopAuth]" audit dump reads this ONE method rather than
    /// restating the negated closed-set walk at every consumer. A
    /// hypothetical `condition-kinds-missing-<n>` require-tag classifier
    /// prefix family that publishes the missing-set cardinality as a
    /// scalar reaches `.missing_condition_kinds().len()`.
    ///
    /// Theory anchor: THEORY.md §II.1 invariant 5 (composition
    /// preserves proofs — the closed-set complement is a typed
    /// projection of [`Self::has_condition_kind`] over
    /// [`ConditionKind::ALL`] under negation, and every downstream
    /// gap-analysis consumer binds through the SAME shape).
    /// THEORY.md §VI.1 (generation over composition — a new
    /// [`ConditionKind`] variant added to `ALL` reaches this method
    /// mechanically through the closed-set walk).
    #[must_use]
    pub fn missing_condition_kinds(&self) -> Vec<ConditionKind> {
        ConditionKind::ALL
            .into_iter()
            .filter(|k| !self.has_condition_kind(*k))
            .collect()
    }

    /// The set of [`ConditionKind`] variants that do NOT appear in
    /// [`Self::preconditions`], projected in [`ConditionKind::ALL`]
    /// order — the precondition-side arm of the (precondition,
    /// postcondition, condition-union) missing-set triad on
    /// [`Boundary`]. Thin typed delegate to
    /// [`ConditionSliceExt::missing_kinds`] over
    /// [`Self::preconditions`].
    ///
    /// Peer of [`Self::missing_postcondition_kinds`] on the
    /// (precondition, postcondition) partition of the boundary's two
    /// condition-vector slots; both peers compose against the SAME
    /// slice-level substrate primitive and their SET-INTERSECTION
    /// (projected in [`ConditionKind::ALL`] order) is
    /// [`Self::missing_condition_kinds`].
    #[must_use]
    pub fn missing_precondition_kinds(&self) -> Vec<ConditionKind> {
        self.preconditions.missing_kinds()
    }

    /// The set of [`ConditionKind`] variants that do NOT appear in
    /// [`Self::postconditions`], projected in [`ConditionKind::ALL`]
    /// order — the postcondition-side arm of the (precondition,
    /// postcondition, condition-union) missing-set triad on
    /// [`Boundary`]. Thin typed delegate to
    /// [`ConditionSliceExt::missing_kinds`] over
    /// [`Self::postconditions`].
    ///
    /// Peer of [`Self::missing_precondition_kinds`]. See that method
    /// for the full rationale — the two methods share ONE lift
    /// motivation, ONE fail-before-pass-after composition-law pin, and
    /// ONE two-surface parity contract with the ephemeral sugar type
    /// via [`crate::ephemeral::EphemeralSpec::missing_postcondition_kinds`].
    #[must_use]
    pub fn missing_postcondition_kinds(&self) -> Vec<ConditionKind> {
        self.postconditions.missing_kinds()
    }

    /// Zero-allocation iterator peer of [`Self::missing_condition_kinds`]
    /// — the condition-union arm of the (precondition, postcondition,
    /// condition-union) closed-set-complement iterator triad on
    /// [`Boundary`]. Walks [`ConditionKind::ALL`] in canonical order and
    /// yields every [`ConditionKind`] that does NOT appear in
    /// `preconditions ∪ postconditions`, WITHOUT materializing an
    /// intermediate `Vec<ConditionKind>`.
    ///
    /// Composed body:
    /// `ConditionKind::ALL.iter().copied().filter(|&k|
    /// !self.has_condition_kind(k))` — a thin projection over the closed
    /// set composed against the two-slice union primitive
    /// [`Self::has_condition_kind`] under a NEGATED predicate, byte-
    /// identical to the trait-level
    /// [`ConditionSliceExt::iter_missing_kinds`] but reaching through
    /// the boundary's two-slice union rather than a single slice.
    /// Equivalent to `self.missing_condition_kinds().into_iter()` without
    /// the intermediate heap allocation.
    ///
    /// Peer on the ephemeral surface — [`crate::ephemeral::EphemeralSpec::iter_missing_condition_kinds`].
    /// Sibling to the three-slice `iter_missing_*_kinds` triad and to the
    /// closed-set-INVERSION peer [`Self::iter_distinct_condition_kinds`] —
    /// the two iterators PARTITION `ConditionKind::ALL` under the
    /// `has_condition_kind` union probe. See
    /// [`Self::missing_condition_kinds`] for the full rationale on the
    /// closed-set-complement aggregate.
    pub fn iter_missing_condition_kinds(&self) -> impl Iterator<Item = ConditionKind> + '_ {
        ConditionKind::ALL
            .iter()
            .copied()
            .filter(|&k| !self.has_condition_kind(k))
    }

    /// Zero-allocation iterator peer of
    /// [`Self::missing_precondition_kinds`] — the precondition-side arm
    /// of the (precondition, postcondition, condition-union) closed-set-
    /// complement iterator triad on [`Boundary`]. Thin typed delegate to
    /// [`ConditionSliceExt::iter_missing_kinds`] over
    /// [`Self::preconditions`].
    pub fn iter_missing_precondition_kinds(&self) -> impl Iterator<Item = ConditionKind> + '_ {
        self.preconditions.iter_missing_kinds()
    }

    /// Zero-allocation iterator peer of
    /// [`Self::missing_postcondition_kinds`] — the postcondition-side arm
    /// of the (precondition, postcondition, condition-union) closed-set-
    /// complement iterator triad on [`Boundary`]. Thin typed delegate to
    /// [`ConditionSliceExt::iter_missing_kinds`] over
    /// [`Self::postconditions`].
    pub fn iter_missing_postcondition_kinds(&self) -> impl Iterator<Item = ConditionKind> + '_ {
        self.postconditions.iter_missing_kinds()
    }

    /// Scalar cardinality of the [`ConditionKind`] set NOT appearing in
    /// `preconditions ∪ postconditions` — the condition-union arm of the
    /// (precondition, postcondition, condition-union) missing-kind-count
    /// triad on [`Boundary`].
    ///
    /// # Composed body
    ///
    /// `ConditionKind::ALL.iter().filter(|k|
    /// !self.has_condition_kind(**k)).count()` — a thin projection over
    /// the closed set composed against the two-slice union primitive
    /// [`Self::has_condition_kind`] under a NEGATED predicate, byte-
    /// identical to the trait-level
    /// [`ConditionSliceExt::missing_kind_count`] but reaching through
    /// the boundary's two-slice union rather than a single slice.
    /// Equivalent to `self.missing_condition_kinds().len()` without
    /// materializing the intermediate `Vec<ConditionKind>`.
    ///
    /// # Sibling to [`Self::missing_condition_kinds`] /
    /// [`Self::distinct_condition_kind_count`]
    ///
    /// Scalar projection of the closed-set-complement widened primitive
    /// on the boundary-union surface — where `missing_condition_kinds`
    /// returns the SET, `missing_condition_kind_count` collapses it to
    /// its cardinality. Byte-for-byte peer of the point-domain scalar
    /// projection [`ConditionSliceExt::missing_kind_count`] one struct-
    /// layer down, and of the peer surface sugar
    /// [`crate::ephemeral::EphemeralSpec::missing_condition_kind_count`]
    /// one struct-layer sideways.
    ///
    /// The scalar-partition composition law
    /// `distinct_condition_kind_count() + missing_condition_kind_count()
    /// == ConditionKind::ALL.len()` binds this method's return to its
    /// distinct-side peer through the closed-set cardinality — the
    /// scalar consequence of the widened-primitive partition law that
    /// [`assert_slice_refinement_composition_laws`] pins on each slice
    /// and that [`crate::assert_surface_union_composition_laws`] lifts
    /// to the two-slice union.
    ///
    /// # Compounding
    ///
    /// A future coherence check that enforces "every process boundary
    /// carries EVERY [`ConditionKind`] under some slot" now reads
    /// `spec.boundary.missing_condition_kind_count() == 0` at ONE call
    /// site rather than paying for
    /// `spec.boundary.missing_condition_kinds().is_empty()` (with its
    /// intermediate heap allocation) or the eight-way negated `has_*_kind`
    /// sweep at the callsite. A future require-tag classifier arm that
    /// publishes the missing-set cardinality as a scalar (a hypothetical
    /// `condition-kinds-missing-<n>` prefix family) reaches this ONE
    /// primitive without allocating.
    ///
    /// Theory anchor: THEORY.md §II.1 invariant 5 — composition
    /// preserves proofs (the scalar cardinality composes the SAME
    /// closed-set walk under negation on both this boundary surface and
    /// the slice-level substrate primitive). THEORY.md §VI.1 —
    /// generation over composition (a new [`ConditionKind`] variant
    /// added to `ALL` reaches this primitive mechanically through the
    /// closed-set walk).
    #[must_use]
    pub fn missing_condition_kind_count(&self) -> usize {
        ConditionKind::ALL
            .iter()
            .filter(|k| !self.has_condition_kind(**k))
            .count()
    }

    /// Scalar cardinality of the [`ConditionKind`] set NOT appearing in
    /// [`Self::preconditions`] — the precondition-side arm of the
    /// (precondition, postcondition, condition-union) missing-kind-count
    /// triad on [`Boundary`]. Thin typed delegate to
    /// [`ConditionSliceExt::missing_kind_count`] over
    /// [`Self::preconditions`].
    ///
    /// Peer of [`Self::missing_postcondition_kind_count`] on the
    /// (precondition, postcondition) partition of the boundary's two
    /// condition-vector slots; both peers compose against the SAME
    /// slice-level substrate primitive so a regression at the per-slice
    /// negated closed-set walk fails at that primitive's tests rather
    /// than as silent drift at either struct-level scalar-cardinality
    /// arm.
    #[must_use]
    pub fn missing_precondition_kind_count(&self) -> usize {
        self.preconditions.missing_kind_count()
    }

    /// Scalar cardinality of the [`ConditionKind`] set NOT appearing in
    /// [`Self::postconditions`] — the postcondition-side arm of the
    /// (precondition, postcondition, condition-union) missing-kind-count
    /// triad on [`Boundary`]. Thin typed delegate to
    /// [`ConditionSliceExt::missing_kind_count`] over
    /// [`Self::postconditions`].
    ///
    /// Peer of [`Self::missing_precondition_kind_count`]. See that
    /// method for the full rationale — the two methods share ONE lift
    /// motivation, ONE fail-before-pass-after composition-law pin, and
    /// ONE two-surface parity contract with the ephemeral sugar type
    /// via
    /// [`crate::ephemeral::EphemeralSpec::missing_postcondition_kind_count`].
    #[must_use]
    pub fn missing_postcondition_kind_count(&self) -> usize {
        self.postconditions.missing_kind_count()
    }

    /// Earliest [`ConditionKind::ALL`] entry present in
    /// `preconditions ∪ postconditions`, or `None` when neither side
    /// populates any variant — the union arm of the (precondition,
    /// postcondition, condition-union) first-distinct-kind triad on
    /// [`Boundary`].
    ///
    /// # Composed body
    ///
    /// `ConditionKind::ALL.iter().copied().find(|k|
    /// self.has_condition_kind(*k))` — a closed-set walk composed
    /// against the two-slice union primitive
    /// [`Self::has_condition_kind`] that SHORT-CIRCUITS at the earliest
    /// match. Byte-identical to the trait-level
    /// [`ConditionSliceExt::first_distinct_kind`] but reaching through
    /// the boundary's two-slice union rather than a single slice.
    /// Equivalent to `self.distinct_condition_kinds().first().copied()`
    /// without materializing the intermediate `Vec<ConditionKind>`.
    ///
    /// # Sibling to [`Self::distinct_condition_kinds`] /
    /// [`Self::distinct_condition_kind_count`]
    ///
    /// Third scalar projection of the closed-set-inversion widened
    /// primitive on the boundary-union surface: `distinct_condition_kinds`
    /// returns the SET, `distinct_condition_kind_count` collapses it to
    /// its cardinality, and `first_distinct_condition_kind` collapses
    /// it to its earliest element. Byte-for-byte peer of the point-domain
    /// scalar projection [`ConditionSliceExt::first_distinct_kind`] one
    /// struct-layer down, and of the peer surface sugar
    /// [`crate::ephemeral::EphemeralSpec::first_distinct_condition_kind`]
    /// one struct-layer sideways.
    ///
    /// # Compounding
    ///
    /// A future coherence check that surfaces "boundary starts with
    /// PromQL" reads `spec.boundary.first_distinct_condition_kind() ==
    /// Some(ConditionKind::PromQL)` at ONE call site rather than
    /// paying for `spec.boundary.distinct_condition_kinds().first() ==
    /// Some(&ConditionKind::PromQL)` (with its intermediate heap
    /// allocation) or the eight-way `has_*_kind` sweep at the callsite.
    /// A future require-tag classifier arm that publishes the earliest
    /// distinct kind as a scalar
    /// (`condition-kinds-first-distinct-<kind>`) reaches this ONE
    /// primitive without allocating.
    ///
    /// Theory anchor: THEORY.md §II.1 invariant 5 — composition
    /// preserves proofs (the earliest-element projection composes the
    /// SAME closed-set walk on both this boundary surface and the
    /// slice-level substrate primitive under short-circuit semantics).
    /// THEORY.md §VI.1 — generation over composition (a new
    /// [`ConditionKind`] variant added to `ALL` reaches this primitive
    /// mechanically through the closed-set walk).
    #[must_use]
    pub fn first_distinct_condition_kind(&self) -> Option<ConditionKind> {
        ConditionKind::ALL
            .iter()
            .copied()
            .find(|k| self.has_condition_kind(*k))
    }

    /// Earliest [`ConditionKind::ALL`] entry present in
    /// [`Self::preconditions`], or `None` when preconditions carry no
    /// matching kind — the precondition-side arm of the (precondition,
    /// postcondition, condition-union) first-distinct-kind triad on
    /// [`Boundary`]. Thin typed delegate to
    /// [`ConditionSliceExt::first_distinct_kind`] over
    /// [`Self::preconditions`].
    ///
    /// Peer of [`Self::first_distinct_postcondition_kind`] on the
    /// (precondition, postcondition) partition of the boundary's two
    /// condition-vector slots; both peers compose against the SAME
    /// slice-level substrate primitive so a regression at the per-slice
    /// short-circuit walk fails at that primitive's tests rather than
    /// as silent drift at either struct-level arm.
    #[must_use]
    pub fn first_distinct_precondition_kind(&self) -> Option<ConditionKind> {
        self.preconditions.first_distinct_kind()
    }

    /// Earliest [`ConditionKind::ALL`] entry present in
    /// [`Self::postconditions`], or `None` when postconditions carry no
    /// matching kind — the postcondition-side arm of the (precondition,
    /// postcondition, condition-union) first-distinct-kind triad on
    /// [`Boundary`]. Thin typed delegate to
    /// [`ConditionSliceExt::first_distinct_kind`] over
    /// [`Self::postconditions`].
    ///
    /// Peer of [`Self::first_distinct_precondition_kind`]. See that
    /// method for the full rationale — the two methods share ONE lift
    /// motivation, ONE fail-before-pass-after composition-law pin, and
    /// ONE two-surface parity contract with the ephemeral sugar type
    /// via
    /// [`crate::ephemeral::EphemeralSpec::first_distinct_postcondition_kind`].
    #[must_use]
    pub fn first_distinct_postcondition_kind(&self) -> Option<ConditionKind> {
        self.postconditions.first_distinct_kind()
    }

    /// Earliest [`ConditionKind::ALL`] entry ABSENT from
    /// `preconditions ∪ postconditions`, or `None` when the union
    /// carries every variant — the union arm of the (precondition,
    /// postcondition, condition-union) first-missing-kind triad on
    /// [`Boundary`].
    ///
    /// # Composed body
    ///
    /// `ConditionKind::ALL.iter().copied().find(|k|
    /// !self.has_condition_kind(*k))` — a closed-set walk composed
    /// against the two-slice union primitive
    /// [`Self::has_condition_kind`] under a NEGATED predicate that
    /// SHORT-CIRCUITS at the earliest empty slot. Byte-identical to the
    /// trait-level [`ConditionSliceExt::first_missing_kind`] but
    /// reaching through the boundary's two-slice union rather than a
    /// single slice. Equivalent to
    /// `self.missing_condition_kinds().first().copied()` without
    /// materializing the intermediate `Vec<ConditionKind>`.
    ///
    /// # Sibling to [`Self::missing_condition_kinds`] /
    /// [`Self::missing_condition_kind_count`]
    ///
    /// Third scalar projection of the closed-set-complement widened
    /// primitive on the boundary-union surface. Byte-for-byte peer of
    /// [`Self::first_distinct_condition_kind`] one axis over under a
    /// negated predicate: where `first_distinct_condition_kind` scalar-
    /// projects the closed-set-INVERSION widened primitive onto its
    /// earliest element, this method scalar-projects the closed-set-
    /// COMPLEMENT widened primitive onto its earliest element.
    ///
    /// # Compounding
    ///
    /// A future coherence check that surfaces "boundary starts missing
    /// ProcessPhase" reads `spec.boundary.first_missing_condition_kind()
    /// == Some(ConditionKind::ProcessPhase)` at ONE call site rather
    /// than paying for `spec.boundary.missing_condition_kinds().first()
    /// == Some(&ConditionKind::ProcessPhase)` (with its intermediate
    /// heap allocation). An operator-facing "first still-unfilled
    /// closed-loop kind" audit reaches this ONE substrate site rather
    /// than restating the negated closed-set walk at every consumer.
    ///
    /// Theory anchor: THEORY.md §II.1 invariant 5 (composition
    /// preserves proofs — the complement-earliest-element projection
    /// composes the SAME closed-set walk on both this boundary surface
    /// and the slice-level substrate primitive under short-circuit
    /// semantics with a negated predicate). THEORY.md §VI.1
    /// (generation over composition — a new [`ConditionKind`] variant
    /// added to `ALL` reaches this primitive mechanically through the
    /// closed-set walk).
    #[must_use]
    pub fn first_missing_condition_kind(&self) -> Option<ConditionKind> {
        ConditionKind::ALL
            .iter()
            .copied()
            .find(|k| !self.has_condition_kind(*k))
    }

    /// Earliest [`ConditionKind::ALL`] entry ABSENT from
    /// [`Self::preconditions`], or `None` when preconditions carry
    /// every variant — the precondition-side arm of the (precondition,
    /// postcondition, condition-union) first-missing-kind triad on
    /// [`Boundary`]. Thin typed delegate to
    /// [`ConditionSliceExt::first_missing_kind`] over
    /// [`Self::preconditions`].
    ///
    /// Peer of [`Self::first_missing_postcondition_kind`] on the
    /// (precondition, postcondition) partition of the boundary's two
    /// condition-vector slots; both peers compose against the SAME
    /// slice-level substrate primitive so a regression at the per-slice
    /// negated short-circuit walk fails at that primitive's tests
    /// rather than as silent drift at either struct-level arm.
    #[must_use]
    pub fn first_missing_precondition_kind(&self) -> Option<ConditionKind> {
        self.preconditions.first_missing_kind()
    }

    /// Earliest [`ConditionKind::ALL`] entry ABSENT from
    /// [`Self::postconditions`], or `None` when postconditions carry
    /// every variant — the postcondition-side arm of the (precondition,
    /// postcondition, condition-union) first-missing-kind triad on
    /// [`Boundary`]. Thin typed delegate to
    /// [`ConditionSliceExt::first_missing_kind`] over
    /// [`Self::postconditions`].
    ///
    /// Peer of [`Self::first_missing_precondition_kind`]. See that
    /// method for the full rationale — the two methods share ONE lift
    /// motivation, ONE fail-before-pass-after composition-law pin, and
    /// ONE two-surface parity contract with the ephemeral sugar type
    /// via
    /// [`crate::ephemeral::EphemeralSpec::first_missing_postcondition_kind`].
    #[must_use]
    pub fn first_missing_postcondition_kind(&self) -> Option<ConditionKind> {
        self.postconditions.first_missing_kind()
    }

    /// Latest [`ConditionKind::ALL`] entry present in
    /// `preconditions ∪ postconditions`, or `None` when neither side
    /// populates any variant — the union arm of the (precondition,
    /// postcondition, condition-union) last-distinct-kind triad on
    /// [`Boundary`].
    ///
    /// # Composed body
    ///
    /// `ConditionKind::ALL.iter().rev().copied().find(|k|
    /// self.has_condition_kind(*k))` — a REVERSED closed-set walk
    /// composed against the two-slice union primitive
    /// [`Self::has_condition_kind`] that SHORT-CIRCUITS at the latest
    /// match. Byte-identical to the trait-level
    /// [`ConditionSliceExt::last_distinct_kind`] but reaching through
    /// the boundary's two-slice union rather than a single slice.
    /// Equivalent to `self.distinct_condition_kinds().last().copied()`
    /// without materializing the intermediate `Vec<ConditionKind>`.
    ///
    /// # Sibling to [`Self::first_distinct_condition_kind`]
    ///
    /// Time-reversed peer of the earliest-element scalar projection
    /// under the SAME two-slice union predicate. Together with
    /// `first_distinct_condition_kind` and the two `_missing_*` peers
    /// the four scalar-endpoint projections close the "endpoint of
    /// closed-set-inversion/complement widened primitive" refinement
    /// axis on the boundary-union surface.
    ///
    /// # Compounding
    ///
    /// A future coherence check that surfaces "boundary ends with
    /// ClosedLoopAuth" reads `spec.boundary.last_distinct_condition_kind()
    /// == Some(ConditionKind::ClosedLoopAuth)` at ONE call site rather
    /// than paying for `spec.boundary.distinct_condition_kinds().last()
    /// == Some(&…)` with its intermediate heap allocation. A future
    /// require-tag classifier arm that publishes the latest distinct
    /// kind as a scalar (`condition-kinds-last-distinct-<kind>`) reaches
    /// this ONE primitive without allocating.
    ///
    /// Theory anchor: THEORY.md §II.1 invariant 5 — composition
    /// preserves proofs (the latest-element projection composes the
    /// SAME reversed closed-set walk on both this boundary surface and
    /// the slice-level substrate primitive under short-circuit
    /// semantics). THEORY.md §VI.1 — generation over composition (a
    /// new [`ConditionKind`] variant added to `ALL` reaches this
    /// primitive mechanically through the reversed closed-set walk).
    #[must_use]
    pub fn last_distinct_condition_kind(&self) -> Option<ConditionKind> {
        ConditionKind::ALL
            .iter()
            .rev()
            .copied()
            .find(|k| self.has_condition_kind(*k))
    }

    /// Latest [`ConditionKind::ALL`] entry present in
    /// [`Self::preconditions`], or `None` when preconditions carry no
    /// matching kind — the precondition-side arm of the (precondition,
    /// postcondition, condition-union) last-distinct-kind triad on
    /// [`Boundary`]. Thin typed delegate to
    /// [`ConditionSliceExt::last_distinct_kind`] over
    /// [`Self::preconditions`].
    ///
    /// Peer of [`Self::last_distinct_postcondition_kind`] on the
    /// (precondition, postcondition) partition of the boundary's two
    /// condition-vector slots; both peers compose against the SAME
    /// slice-level substrate primitive so a regression at the per-
    /// slice REVERSED short-circuit walk fails at that primitive's
    /// tests rather than as silent drift at either struct-level arm.
    #[must_use]
    pub fn last_distinct_precondition_kind(&self) -> Option<ConditionKind> {
        self.preconditions.last_distinct_kind()
    }

    /// Latest [`ConditionKind::ALL`] entry present in
    /// [`Self::postconditions`], or `None` when postconditions carry
    /// no matching kind — the postcondition-side arm of the
    /// (precondition, postcondition, condition-union) last-distinct-
    /// kind triad on [`Boundary`]. Thin typed delegate to
    /// [`ConditionSliceExt::last_distinct_kind`] over
    /// [`Self::postconditions`].
    ///
    /// Peer of [`Self::last_distinct_precondition_kind`]. See that
    /// method for the full rationale — the two methods share ONE lift
    /// motivation, ONE fail-before-pass-after composition-law pin, and
    /// ONE two-surface parity contract with the ephemeral sugar type
    /// via
    /// [`crate::ephemeral::EphemeralSpec::last_distinct_postcondition_kind`].
    #[must_use]
    pub fn last_distinct_postcondition_kind(&self) -> Option<ConditionKind> {
        self.postconditions.last_distinct_kind()
    }

    /// Latest [`ConditionKind::ALL`] entry ABSENT from
    /// `preconditions ∪ postconditions`, or `None` when the union
    /// carries every variant — the union arm of the (precondition,
    /// postcondition, condition-union) last-missing-kind triad on
    /// [`Boundary`].
    ///
    /// # Composed body
    ///
    /// `ConditionKind::ALL.iter().rev().copied().find(|k|
    /// !self.has_condition_kind(*k))` — a REVERSED closed-set walk
    /// composed against the two-slice union primitive
    /// [`Self::has_condition_kind`] under a NEGATED predicate that
    /// SHORT-CIRCUITS at the latest empty slot. Byte-identical to the
    /// trait-level [`ConditionSliceExt::last_missing_kind`] but
    /// reaching through the boundary's two-slice union rather than a
    /// single slice. Equivalent to
    /// `self.missing_condition_kinds().last().copied()` without
    /// materializing the intermediate `Vec<ConditionKind>`.
    ///
    /// # Sibling to [`Self::first_missing_condition_kind`]
    ///
    /// Time-reversed peer of the earliest-element scalar projection
    /// under the SAME negated two-slice union predicate. Fourth
    /// scalar projection on the closed-set-complement axis on the
    /// boundary-union surface (first, count, missing_kinds already
    /// shipped; this method closes the endpoint pair on the
    /// complement side).
    ///
    /// # Compounding
    ///
    /// A future coherence check that surfaces "boundary is latest-
    /// missing PromQL" reads
    /// `spec.boundary.last_missing_condition_kind() ==
    /// Some(ConditionKind::PromQL)` at ONE call site rather than
    /// paying for `spec.boundary.missing_condition_kinds().last()`
    /// with its intermediate heap allocation. An operator-facing
    /// "last still-unfilled closed-loop kind" audit reaches this ONE
    /// substrate site rather than restating the negated reversed
    /// closed-set walk at every consumer.
    ///
    /// Theory anchor: THEORY.md §II.1 invariant 5 (composition
    /// preserves proofs — the complement-latest-element projection
    /// composes the SAME reversed closed-set walk on both this
    /// boundary surface and the slice-level substrate primitive
    /// under short-circuit semantics with a negated predicate).
    /// THEORY.md §VI.1 (generation over composition — a new
    /// [`ConditionKind`] variant added to `ALL` reaches this
    /// primitive mechanically through the reversed closed-set walk).
    #[must_use]
    pub fn last_missing_condition_kind(&self) -> Option<ConditionKind> {
        ConditionKind::ALL
            .iter()
            .rev()
            .copied()
            .find(|k| !self.has_condition_kind(*k))
    }

    /// Latest [`ConditionKind::ALL`] entry ABSENT from
    /// [`Self::preconditions`], or `None` when preconditions carry
    /// every variant — the precondition-side arm of the (precondition,
    /// postcondition, condition-union) last-missing-kind triad on
    /// [`Boundary`]. Thin typed delegate to
    /// [`ConditionSliceExt::last_missing_kind`] over
    /// [`Self::preconditions`].
    ///
    /// Peer of [`Self::last_missing_postcondition_kind`] on the
    /// (precondition, postcondition) partition of the boundary's two
    /// condition-vector slots; both peers compose against the SAME
    /// slice-level substrate primitive so a regression at the per-
    /// slice negated REVERSED short-circuit walk fails at that
    /// primitive's tests rather than as silent drift at either
    /// struct-level arm.
    #[must_use]
    pub fn last_missing_precondition_kind(&self) -> Option<ConditionKind> {
        self.preconditions.last_missing_kind()
    }

    /// Latest [`ConditionKind::ALL`] entry ABSENT from
    /// [`Self::postconditions`], or `None` when postconditions carry
    /// every variant — the postcondition-side arm of the (precondition,
    /// postcondition, condition-union) last-missing-kind triad on
    /// [`Boundary`]. Thin typed delegate to
    /// [`ConditionSliceExt::last_missing_kind`] over
    /// [`Self::postconditions`].
    ///
    /// Peer of [`Self::last_missing_precondition_kind`]. See that
    /// method for the full rationale — the two methods share ONE lift
    /// motivation, ONE fail-before-pass-after composition-law pin, and
    /// ONE two-surface parity contract with the ephemeral sugar type
    /// via
    /// [`crate::ephemeral::EphemeralSpec::last_missing_postcondition_kind`].
    #[must_use]
    pub fn last_missing_postcondition_kind(&self) -> Option<ConditionKind> {
        self.postconditions.last_missing_kind()
    }

    /// `true` iff `preconditions ∪ postconditions` carries every
    /// [`ConditionKind::ALL`] variant at least once — the union arm
    /// of the (precondition, postcondition, condition-union)
    /// saturation-predicate triad on [`Boundary`].
    ///
    /// # Composed body
    ///
    /// `ConditionKind::ALL.iter().all(|k| self.has_condition_kind(*k))`
    /// — a SHORT-CIRCUITING closed-set walk composed against the
    /// two-slice union primitive [`Self::has_condition_kind`], byte-
    /// identical to the trait-level [`ConditionSliceExt::is_kind_saturated`]
    /// but reaching through the boundary's two-slice union rather than
    /// a single slice. Equivalent to `self.missing_condition_kinds()
    /// .is_empty()` without materializing the `Vec<ConditionKind>`, and
    /// to `self.missing_condition_kind_count() == 0` without paying for
    /// the counter walk on every arm.
    ///
    /// # Peer on the ephemeral surface — [`crate::ephemeral::EphemeralSpec::is_condition_kind_saturated`]
    ///
    /// Byte-identical signature `(&Self) -> bool`, byte-identical
    /// closed-set-walk body, on the sugar-surface type whose pre/post
    /// condition vectors live directly on the struct. Both methods
    /// compose against the SAME slice-level substrate primitive
    /// [`ConditionSliceExt::is_kind_saturated`] via the two-slice
    /// union composed through [`Self::has_condition_kind`] — a
    /// regression at the per-slice `all` short-circuit fails at that
    /// primitive's tests rather than as silent drift at either
    /// struct-level saturation caller.
    ///
    /// Theory anchor: THEORY.md §II.1 invariant 5 — composition
    /// preserves proofs (the saturation-endpoint projection composes
    /// the SAME closed-set walk on both this boundary surface and the
    /// slice-level substrate primitive under short-circuit semantics).
    /// THEORY.md §VI.1 — generation over composition (a new
    /// [`ConditionKind`] variant added to `ALL` reaches this primitive
    /// mechanically through the `all` short-circuit).
    #[must_use]
    pub fn is_condition_kind_saturated(&self) -> bool {
        ConditionKind::ALL
            .iter()
            .all(|k| self.has_condition_kind(*k))
    }

    /// `true` iff [`Self::preconditions`] carries every
    /// [`ConditionKind::ALL`] variant at least once — the precondition-
    /// side arm of the (precondition, postcondition, condition-union)
    /// saturation-predicate triad on [`Boundary`]. Thin typed delegate
    /// to [`ConditionSliceExt::is_kind_saturated`] over
    /// [`Self::preconditions`].
    ///
    /// Peer of [`Self::is_postcondition_kind_saturated`] on the
    /// (precondition, postcondition) partition of the boundary's two
    /// condition-vector slots; both peers compose against the SAME
    /// slice-level substrate primitive so a regression at the per-
    /// slice `all` short-circuit fails at that primitive's tests
    /// rather than as silent drift at either struct-level arm.
    #[must_use]
    pub fn is_precondition_kind_saturated(&self) -> bool {
        self.preconditions.is_kind_saturated()
    }

    /// `true` iff [`Self::postconditions`] carries every
    /// [`ConditionKind::ALL`] variant at least once — the postcondition-
    /// side arm of the (precondition, postcondition, condition-union)
    /// saturation-predicate triad on [`Boundary`]. Thin typed delegate
    /// to [`ConditionSliceExt::is_kind_saturated`] over
    /// [`Self::postconditions`].
    ///
    /// Peer of [`Self::is_precondition_kind_saturated`]. See that
    /// method for the full rationale — the two methods share ONE lift
    /// motivation, ONE fail-before-pass-after composition-law pin, and
    /// ONE two-surface parity contract with the ephemeral sugar type
    /// via
    /// [`crate::ephemeral::EphemeralSpec::is_postcondition_kind_saturated`].
    #[must_use]
    pub fn is_postcondition_kind_saturated(&self) -> bool {
        self.postconditions.is_kind_saturated()
    }

    /// `true` iff `preconditions ∪ postconditions` is MISSING at least
    /// one [`ConditionKind::ALL`] variant — the union arm of the
    /// (precondition, postcondition, condition-union) at-least-one
    /// halfspace triad on [`Boundary`], byte-for-byte peer of the
    /// saturation-predicate triad
    /// [`Self::is_condition_kind_saturated`] under a definitional
    /// negation.
    ///
    /// # Composed body
    ///
    /// `!self.is_condition_kind_saturated()` — the definitional
    /// negation of the two-slice union saturation primitive. The
    /// underlying `ConditionKind::ALL.iter().all(has_condition_kind)`
    /// walk returns `false` at the FIRST missing kind (yielding `true`
    /// here) WITHOUT materializing
    /// [`Self::missing_condition_kinds`]'s `Vec` and WITHOUT walking
    /// every entry to build [`Self::missing_condition_kind_count`]'s
    /// scalar. Strictly cheaper than either widened primitive on every
    /// partially-populated arm.
    ///
    /// # Peer on the ephemeral surface — [`crate::ephemeral::EphemeralSpec::has_any_missing_condition_kind`]
    ///
    /// Byte-identical signature `(&Self) -> bool`, byte-identical
    /// `!self.is_condition_kind_saturated()` body, on the sugar-surface
    /// type whose pre/post condition vectors live directly on the
    /// struct. Both methods compose against the SAME slice-level
    /// substrate primitive [`ConditionSliceExt::has_any_missing_kind`]
    /// via the two-slice union composed through
    /// [`Self::is_condition_kind_saturated`] — a regression at the
    /// per-slice `all` short-circuit fails at that primitive's tests
    /// rather than as silent drift at either struct-level at-least-one
    /// halfspace caller.
    ///
    /// # Compounding
    ///
    /// A `has-any-missing-kind` require-tag classifier arm — byte-
    /// for-byte peer of the tagged-union `has-any-missing-kind`
    /// classifier one struct-layer up + the saturation-predicate
    /// triad's negated dual — reaches this primitive at ONE call
    /// site rather than negating `boundary.is_condition_kind_saturated()`
    /// at the callsite or restating
    /// `boundary.missing_condition_kind_count() > 0` (which walks
    /// every slot to count) or
    /// `!boundary.missing_condition_kinds().is_empty()` (which
    /// allocates the Vec before the negated emptiness check).
    ///
    /// Theory anchor: THEORY.md §II.1 invariant 5 (composition
    /// preserves proofs — the at-least-one halfspace projection
    /// composes the SAME two-slice union negation on both this
    /// boundary surface and the slice-level substrate primitive under
    /// definitional negation). THEORY.md §VI.1 (generation over
    /// composition — a new [`ConditionKind`] variant reaches both
    /// surfaces' at-least-one halfspace triads mechanically through
    /// the delegated union primitive).
    #[must_use]
    pub fn has_any_missing_condition_kind(&self) -> bool {
        !self.is_condition_kind_saturated()
    }

    /// `true` iff [`Self::preconditions`] is MISSING at least one
    /// [`ConditionKind::ALL`] variant — the precondition-side arm of
    /// the (precondition, postcondition, condition-union) at-least-
    /// one halfspace triad on [`Boundary`]. Thin typed delegate to
    /// [`ConditionSliceExt::has_any_missing_kind`] over
    /// [`Self::preconditions`].
    ///
    /// Peer of [`Self::has_any_missing_postcondition_kind`] on the
    /// (precondition, postcondition) partition of the boundary's two
    /// condition-vector slots; both peers compose against the SAME
    /// slice-level substrate primitive so a regression at the per-
    /// slice `all` short-circuit under negation fails at that
    /// primitive's tests rather than as silent drift at either
    /// struct-level arm.
    #[must_use]
    pub fn has_any_missing_precondition_kind(&self) -> bool {
        self.preconditions.has_any_missing_kind()
    }

    /// `true` iff [`Self::postconditions`] is MISSING at least one
    /// [`ConditionKind::ALL`] variant — the postcondition-side arm of
    /// the (precondition, postcondition, condition-union) at-least-
    /// one halfspace triad on [`Boundary`]. Thin typed delegate to
    /// [`ConditionSliceExt::has_any_missing_kind`] over
    /// [`Self::postconditions`].
    ///
    /// Peer of [`Self::has_any_missing_precondition_kind`]. See that
    /// method for the full rationale — the two methods share ONE lift
    /// motivation, ONE fail-before-pass-after composition-law pin, and
    /// ONE two-surface parity contract with the ephemeral sugar type
    /// via
    /// [`crate::ephemeral::EphemeralSpec::has_any_missing_postcondition_kind`].
    #[must_use]
    pub fn has_any_missing_postcondition_kind(&self) -> bool {
        self.postconditions.has_any_missing_kind()
    }

    /// `true` iff `preconditions ∪ postconditions` carries at least one
    /// [`ConditionKind::ALL`] variant — the union arm of the
    /// (precondition, postcondition, condition-union) at-least-one
    /// halfspace triad on [`Boundary`] on the closed-set-inversion
    /// axis, byte-for-byte peer of the at-least-one halfspace triad
    /// [`Self::has_any_missing_condition_kind`] on the closed-set-
    /// complement axis.
    ///
    /// # Composed body
    ///
    /// `ConditionKind::ALL.iter().copied().any(|k|
    /// self.has_condition_kind(k))` — a SHORT-CIRCUITING closed-set
    /// walk under the two-slice union primitive
    /// [`Self::has_condition_kind`]. The walk returns `true` at the
    /// FIRST kind present in EITHER slice WITHOUT materializing
    /// [`Self::distinct_condition_kinds`]'s `Vec` and WITHOUT walking
    /// every kind to build [`Self::distinct_condition_kind_count`]'s
    /// scalar. Strictly cheaper than either widened primitive on every
    /// non-empty arm because the walk short-circuits at the first
    /// populated kind rather than paying for the Vec allocation or the
    /// full cardinality count.
    ///
    /// # Peer on the ephemeral surface — [`crate::ephemeral::EphemeralSpec::has_any_distinct_condition_kind`]
    ///
    /// Byte-identical signature `(&Self) -> bool`, byte-identical
    /// `ConditionKind::ALL.iter().copied().any(|k|
    /// self.has_condition_kind(k))` body, on the sugar-surface type
    /// whose pre/post condition vectors live directly on the struct.
    /// Both methods compose against the SAME slice-level substrate
    /// primitive [`ConditionSliceExt::has_any_distinct_kind`] via the
    /// two-slice union through [`Self::has_condition_kind`] — a
    /// regression at the per-slice `any` short-circuit fails at that
    /// primitive's tests rather than as silent drift at either struct-
    /// level at-least-one halfspace caller.
    ///
    /// # Compounding
    ///
    /// A `has-any-distinct-condition-kind` require-tag classifier arm
    /// — byte-for-byte peer of the tagged-union `has-any-populated-
    /// kind` classifier one struct-layer up + the at-least-one
    /// halfspace triad's closed-set-inversion peer — reaches this
    /// primitive at ONE call site rather than restating
    /// `boundary.distinct_condition_kind_count() > 0` (which walks
    /// every kind to count) or
    /// `!boundary.distinct_condition_kinds().is_empty()` (which
    /// allocates the Vec before the negated emptiness check).
    ///
    /// Theory anchor: THEORY.md §II.1 invariant 5 (composition
    /// preserves proofs — the at-least-one halfspace projection
    /// composes the SAME closed-set walk on both this boundary surface
    /// and the slice-level substrate primitive under short-circuit
    /// semantics). THEORY.md §VI.1 (generation over composition — a
    /// new [`ConditionKind`] variant reaches both surfaces' at-least-
    /// one halfspace triads mechanically through the delegated union
    /// primitive).
    #[must_use]
    pub fn has_any_distinct_condition_kind(&self) -> bool {
        ConditionKind::ALL
            .iter()
            .copied()
            .any(|k| self.has_condition_kind(k))
    }

    /// `true` iff [`Self::preconditions`] carries at least one
    /// [`ConditionKind::ALL`] variant — the precondition-side arm of
    /// the (precondition, postcondition, condition-union) at-least-one
    /// halfspace triad on [`Boundary`] on the closed-set-inversion
    /// axis. Thin typed delegate to
    /// [`ConditionSliceExt::has_any_distinct_kind`] over
    /// [`Self::preconditions`].
    ///
    /// Peer of [`Self::has_any_distinct_postcondition_kind`] on the
    /// (precondition, postcondition) partition of the boundary's two
    /// condition-vector slots; both peers compose against the SAME
    /// slice-level substrate primitive so a regression at the per-
    /// slice `any` short-circuit fails at that primitive's tests
    /// rather than as silent drift at either struct-level arm.
    #[must_use]
    pub fn has_any_distinct_precondition_kind(&self) -> bool {
        self.preconditions.has_any_distinct_kind()
    }

    /// `true` iff [`Self::postconditions`] carries at least one
    /// [`ConditionKind::ALL`] variant — the postcondition-side arm of
    /// the (precondition, postcondition, condition-union) at-least-one
    /// halfspace triad on [`Boundary`] on the closed-set-inversion
    /// axis. Thin typed delegate to
    /// [`ConditionSliceExt::has_any_distinct_kind`] over
    /// [`Self::postconditions`].
    ///
    /// Peer of [`Self::has_any_distinct_precondition_kind`]. See that
    /// method for the full rationale — the two methods share ONE lift
    /// motivation, ONE fail-before-pass-after composition-law pin, and
    /// ONE two-surface parity contract with the ephemeral sugar type
    /// via
    /// [`crate::ephemeral::EphemeralSpec::has_any_distinct_postcondition_kind`].
    #[must_use]
    pub fn has_any_distinct_postcondition_kind(&self) -> bool {
        self.postconditions.has_any_distinct_kind()
    }

    /// `true` iff `preconditions ∪ postconditions` carries EXACTLY
    /// ONE [`ConditionKind::ALL`] variant — the union arm of the
    /// (precondition, postcondition, condition-union) cardinality-mid-
    /// endpoint triad on [`Boundary`] closing the singleton-coverage
    /// arm on the closed-set-inversion axis on the union of the two
    /// condition slots. The Boolean cardinality-mid-endpoint fast-
    /// path peer of [`Self::has_any_distinct_condition_kind`] (≥1
    /// halfspace) on the union axis: where the at-least-one halfspace
    /// predicate answers "is ANY kind covered by the union?",
    /// `has_unique_distinct_condition_kind` answers "is EXACTLY ONE
    /// kind covered by the union?".
    ///
    /// Composed body: constructs a two-step-short-circuit walk over
    /// [`ConditionKind::ALL`] under the [`Self::has_condition_kind`]
    /// union primitive — pulls up to two hits off the filtered
    /// iterator; the primitive returns `true` iff the first is
    /// [`Some`] and the second is [`None`]. Byte-for-byte peer of
    /// [`ConditionSliceExt::has_unique_distinct_kind`] one slice-
    /// layer down, lifted to compose against
    /// [`Self::has_condition_kind`]'s pre-OR-post union rather than
    /// against a single slice's `has_kind`. A regression at the union
    /// primitive fails at the slice-level substrate tests + the union
    /// composition-law tests rather than as silent drift here.
    ///
    /// # Peer on the ephemeral surface — [`crate::ephemeral::EphemeralSpec::has_unique_distinct_condition_kind`]
    ///
    /// Byte-identical signature `(&Self) -> bool`, byte-identical
    /// two-step short-circuit body composed against the ephemeral
    /// surface's own union primitive. Both methods compose against
    /// the SAME slice-level substrate primitive
    /// [`ConditionSliceExt::has_unique_distinct_kind`] via the
    /// two-slice union — a regression at the per-slice singleton-
    /// coverage walk fails at that primitive's tests rather than as
    /// silent drift at either struct-level singleton-coverage caller.
    ///
    /// # Sibling to [`Self::has_unique_missing_condition_kind`]
    ///
    /// Closed-set-inversion peer of the cardinality-mid-endpoint on
    /// the closed-set-complement axis at the boundary union struct
    /// layer — where `has_unique_missing_condition_kind` returns
    /// `true` iff the union is one kind AWAY from covered (missing
    /// EXACTLY one), `has_unique_distinct_condition_kind` returns
    /// `true` iff the union covers EXACTLY one kind (the singleton-
    /// coverage arm). Both compose against a two-step-short-circuit
    /// walk over [`ConditionKind::ALL`] under
    /// [`Self::has_condition_kind`] (this primitive) vs
    /// `!has_condition_kind` (the missing peer).
    ///
    /// Theory anchor: THEORY.md §II.1 invariant 5 (composition
    /// preserves proofs — the cardinality-mid-endpoint projection on
    /// the closed-set-inversion axis composes the SAME two-step
    /// short-circuit walk under a two-slice union on both this
    /// boundary surface and the ephemeral surface). THEORY.md §VI.1
    /// (generation over composition — a new [`ConditionKind`]
    /// variant reaches both surfaces' cardinality-mid-endpoint triads
    /// mechanically through the delegated union primitive).
    #[must_use]
    pub fn has_unique_distinct_condition_kind(&self) -> bool {
        let mut it = ConditionKind::ALL
            .iter()
            .copied()
            .filter(|k| self.has_condition_kind(*k));
        it.next().is_some() && it.next().is_none()
    }

    /// `true` iff [`Self::preconditions`] carries EXACTLY ONE
    /// [`ConditionKind::ALL`] variant — the precondition-side arm of
    /// the (precondition, postcondition, condition-union)
    /// cardinality-mid-endpoint triad on [`Boundary`] on the closed-
    /// set-inversion axis. Thin typed delegate to
    /// [`ConditionSliceExt::has_unique_distinct_kind`] over
    /// [`Self::preconditions`].
    ///
    /// Peer of [`Self::has_unique_distinct_postcondition_kind`] on the
    /// (precondition, postcondition) partition of the boundary's two
    /// condition-vector slots; both peers compose against the SAME
    /// slice-level substrate primitive so a regression at the per-
    /// slice two-step short-circuit walk fails at that primitive's
    /// tests rather than as silent drift at either struct-level arm.
    #[must_use]
    pub fn has_unique_distinct_precondition_kind(&self) -> bool {
        self.preconditions.has_unique_distinct_kind()
    }

    /// `true` iff [`Self::postconditions`] carries EXACTLY ONE
    /// [`ConditionKind::ALL`] variant — the postcondition-side arm of
    /// the (precondition, postcondition, condition-union)
    /// cardinality-mid-endpoint triad on [`Boundary`] on the closed-
    /// set-inversion axis. Thin typed delegate to
    /// [`ConditionSliceExt::has_unique_distinct_kind`] over
    /// [`Self::postconditions`].
    ///
    /// Peer of [`Self::has_unique_distinct_precondition_kind`]. See
    /// that method for the full rationale — the two methods share ONE
    /// lift motivation, ONE fail-before-pass-after composition-law
    /// pin, and ONE two-surface parity contract with the ephemeral
    /// sugar type via
    /// [`crate::ephemeral::EphemeralSpec::has_unique_distinct_postcondition_kind`].
    #[must_use]
    pub fn has_unique_distinct_postcondition_kind(&self) -> bool {
        self.postconditions.has_unique_distinct_kind()
    }

    /// The SOLE [`ConditionKind::ALL`] variant covered by
    /// `preconditions ∪ postconditions`, or `None` when the union
    /// covers 0 or ≥ 2 kinds — the union arm of the (precondition,
    /// postcondition, condition-union) exactly-one-hit witnessing
    /// triad on [`Boundary`] closing the singleton-coverage witness on
    /// the closed-set-inversion axis on the union of the two condition
    /// slots. Witnessing scalar peer of
    /// [`Self::has_unique_distinct_condition_kind`] (=1 predicate) on
    /// the union axis: where the Boolean predicate answers "does the
    /// union cover EXACTLY one kind?", `unique_distinct_condition_kind`
    /// returns `Some(k)` naming that SOLE kind (or `None` on the 0 or
    /// ≥ 2 arms).
    ///
    /// # Composed body
    ///
    /// A two-step-short-circuit walk over [`ConditionKind::ALL`] under
    /// the [`Self::has_condition_kind`] union primitive — pull the
    /// first hit; return `Some(first)` iff the second hit is [`None`],
    /// else `None`. Byte-for-byte peer of
    /// [`ConditionSliceExt::unique_distinct_kind`] one slice-layer
    /// down, lifted to compose against
    /// [`Self::has_condition_kind`]'s pre-OR-post union rather than
    /// against a single slice's `has_kind`. A regression at the union
    /// primitive fails at the slice-level substrate tests + the union
    /// composition-law tests rather than as silent drift here.
    ///
    /// # Peer on the ephemeral surface — [`crate::ephemeral::EphemeralSpec::unique_distinct_condition_kind`]
    ///
    /// Byte-identical signature `(&Self) -> Option<ConditionKind>`,
    /// byte-identical two-step short-circuit body composed against the
    /// ephemeral surface's own union primitive. Both methods compose
    /// against the SAME slice-level substrate primitive
    /// [`ConditionSliceExt::unique_distinct_kind`] via the two-slice
    /// union — a regression at the per-slice singleton-coverage
    /// witnessing walk fails at that primitive's tests rather than as
    /// silent drift at either struct-level singleton-coverage caller.
    ///
    /// # Sibling to [`Self::unique_missing_condition_kind`]
    ///
    /// Closed-set-inversion peer of the exactly-one-hit witness on the
    /// closed-set-complement axis at the boundary union struct layer —
    /// where `unique_missing_condition_kind` names the SOLE kind AWAY
    /// from covered, `unique_distinct_condition_kind` names the SOLE
    /// kind covered. Both compose against a two-step-short-circuit walk
    /// over [`ConditionKind::ALL`] under [`Self::has_condition_kind`]
    /// (this primitive) vs `!has_condition_kind` (the missing peer).
    ///
    /// Theory anchor: THEORY.md §II.1 invariant 5 (composition
    /// preserves proofs — the exactly-one-hit witnessing projection on
    /// the closed-set-inversion axis composes the SAME two-step short-
    /// circuit walk under a two-slice union on both this boundary
    /// surface and the ephemeral surface). THEORY.md §VI.1 (generation
    /// over composition — a new [`ConditionKind`] variant reaches both
    /// surfaces' unique-distinct-kind triads mechanically through the
    /// delegated union primitive).
    #[must_use]
    pub fn unique_distinct_condition_kind(&self) -> Option<ConditionKind> {
        let mut it = ConditionKind::ALL
            .iter()
            .copied()
            .filter(|k| self.has_condition_kind(*k));
        let first = it.next()?;
        match it.next() {
            None => Some(first),
            Some(_) => None,
        }
    }

    /// The SOLE [`ConditionKind::ALL`] variant covered by
    /// [`Self::preconditions`], or `None` when preconditions cover 0
    /// or ≥ 2 kinds — the precondition-side arm of the (precondition,
    /// postcondition, condition-union) exactly-one-hit witnessing
    /// triad on [`Boundary`] on the closed-set-inversion axis. Thin
    /// typed delegate to [`ConditionSliceExt::unique_distinct_kind`]
    /// over [`Self::preconditions`].
    ///
    /// Peer of [`Self::unique_distinct_postcondition_kind`] on the
    /// (precondition, postcondition) partition of the boundary's two
    /// condition-vector slots; both peers compose against the SAME
    /// slice-level substrate primitive so a regression at the per-
    /// slice two-step short-circuit witnessing walk fails at that
    /// primitive's tests rather than as silent drift at either
    /// struct-level arm.
    #[must_use]
    pub fn unique_distinct_precondition_kind(&self) -> Option<ConditionKind> {
        self.preconditions.unique_distinct_kind()
    }

    /// The SOLE [`ConditionKind::ALL`] variant covered by
    /// [`Self::postconditions`], or `None` when postconditions cover 0
    /// or ≥ 2 kinds — the postcondition-side arm of the (precondition,
    /// postcondition, condition-union) exactly-one-hit witnessing
    /// triad on [`Boundary`] on the closed-set-inversion axis. Thin
    /// typed delegate to [`ConditionSliceExt::unique_distinct_kind`]
    /// over [`Self::postconditions`].
    ///
    /// Peer of [`Self::unique_distinct_precondition_kind`]. See that
    /// method for the full rationale — the two methods share ONE lift
    /// motivation, ONE fail-before-pass-after composition-law pin, and
    /// ONE two-surface parity contract with the ephemeral sugar type
    /// via
    /// [`crate::ephemeral::EphemeralSpec::unique_distinct_postcondition_kind`].
    #[must_use]
    pub fn unique_distinct_postcondition_kind(&self) -> Option<ConditionKind> {
        self.postconditions.unique_distinct_kind()
    }

    /// `true` iff `preconditions ∪ postconditions` COVERS AT LEAST
    /// TWO [`ConditionKind::ALL`] variants — the union arm of the
    /// (precondition, postcondition, condition-union) cardinality-
    /// many-arm triad on [`Boundary`] closing the "≥ 2 kinds covered"
    /// arm on the union of the two condition slots. The many-arm
    /// Boolean fast-path peer of
    /// [`Self::has_unique_distinct_condition_kind`] (=1 arm) and
    /// [`Self::has_any_distinct_condition_kind`] (≥1 halfspace) on the
    /// union axis, closing the {0, 1, ≥2} trichotomy on the distinct
    /// axis at the union struct layer.
    ///
    /// Composed body: constructs a two-step-short-circuit walk over
    /// [`ConditionKind::ALL`] under the [`Self::has_condition_kind`]
    /// union primitive — pulls up to two hits off the filtered
    /// iterator; the primitive returns `true` iff BOTH the first and
    /// the second are [`Some`]. Byte-for-byte peer of
    /// [`ConditionSliceExt::has_multiple_distinct_kinds`] one slice-
    /// layer down, lifted to compose against
    /// [`Self::has_condition_kind`]'s pre-OR-post union rather than
    /// against a single slice's `has_kind`. A regression at the union
    /// primitive fails at the slice-level substrate tests + the union
    /// composition-law tests rather than as silent drift here.
    ///
    /// # Peer on the ephemeral surface — [`crate::ephemeral::EphemeralSpec::has_multiple_distinct_condition_kind`]
    ///
    /// Byte-identical signature `(&Self) -> bool`, byte-identical
    /// two-step short-circuit body composed against the ephemeral
    /// surface's own union primitive. Both methods compose against
    /// the SAME slice-level substrate primitive
    /// [`ConditionSliceExt::has_multiple_distinct_kinds`] via the
    /// two-slice union — a regression at the per-slice many-arm walk
    /// fails at that primitive's tests rather than as silent drift at
    /// either struct-level many-distinct caller.
    ///
    /// # Sibling to [`Self::has_multiple_missing_condition_kind`]
    ///
    /// Closed-set-inversion peer of the cardinality-many-arm on the
    /// closed-set-complement axis at the boundary union struct layer
    /// — where `has_multiple_missing_condition_kind` returns `true`
    /// iff the union has ≥ 2 kinds ABSENT, `has_multiple_distinct_condition_kind`
    /// returns `true` iff the union covers ≥ 2 kinds. Both compose
    /// against a two-step-short-circuit walk over [`ConditionKind::ALL`]
    /// under [`Self::has_condition_kind`] (this primitive) vs
    /// `!has_condition_kind` (the missing peer).
    ///
    /// # Compounding
    ///
    /// A future operator-facing "≥ 2 dependencies covered" fast-path
    /// diagnostic reads `boundary.has_multiple_distinct_condition_kind()`
    /// at ONE call site rather than restating
    /// `boundary.distinct_condition_kind_count() >= 2` (which walks
    /// every slot to count) or
    /// `boundary.distinct_condition_kinds().len() >= 2` (which
    /// allocates the Vec). A `has-multiple-distinct-condition-kind`
    /// require-tag classifier arm reaches this primitive at ONE
    /// substrate call — byte-for-byte peer of the tagged-union
    /// `has-multiple-populated-kinds` classifier one struct-layer up.
    ///
    /// Theory anchor: THEORY.md §II.1 invariant 5 (composition
    /// preserves proofs — the cardinality-many-arm projection on the
    /// closed-set-inversion axis composes the SAME two-step short-
    /// circuit walk under a two-slice union on both this boundary
    /// surface and the ephemeral surface). THEORY.md §VI.1
    /// (generation over composition — a new [`ConditionKind`]
    /// variant reaches both surfaces' cardinality-many-arm triads
    /// mechanically through the delegated union primitive).
    #[must_use]
    pub fn has_multiple_distinct_condition_kind(&self) -> bool {
        let mut it = ConditionKind::ALL
            .iter()
            .copied()
            .filter(|k| self.has_condition_kind(*k));
        it.next().is_some() && it.next().is_some()
    }

    /// `true` iff [`Self::preconditions`] carries AT LEAST TWO
    /// [`ConditionKind::ALL`] variants — the precondition-side arm of
    /// the (precondition, postcondition, condition-union) cardinality-
    /// many-arm triad on [`Boundary`] on the closed-set-inversion axis.
    /// Thin typed delegate to
    /// [`ConditionSliceExt::has_multiple_distinct_kinds`] over
    /// [`Self::preconditions`].
    ///
    /// Peer of [`Self::has_multiple_distinct_postcondition_kind`] on
    /// the (precondition, postcondition) partition of the boundary's
    /// two condition-vector slots; both peers compose against the
    /// SAME slice-level substrate primitive so a regression at the
    /// per-slice two-step short-circuit walk fails at that primitive's
    /// tests rather than as silent drift at either struct-level arm.
    #[must_use]
    pub fn has_multiple_distinct_precondition_kind(&self) -> bool {
        self.preconditions.has_multiple_distinct_kinds()
    }

    /// `true` iff [`Self::postconditions`] carries AT LEAST TWO
    /// [`ConditionKind::ALL`] variants — the postcondition-side arm of
    /// the (precondition, postcondition, condition-union) cardinality-
    /// many-arm triad on [`Boundary`] on the closed-set-inversion axis.
    /// Thin typed delegate to
    /// [`ConditionSliceExt::has_multiple_distinct_kinds`] over
    /// [`Self::postconditions`].
    ///
    /// Peer of [`Self::has_multiple_distinct_precondition_kind`]. See
    /// that method for the full rationale — the two methods share ONE
    /// lift motivation, ONE fail-before-pass-after composition-law
    /// pin, and ONE two-surface parity contract with the ephemeral
    /// sugar type via
    /// [`crate::ephemeral::EphemeralSpec::has_multiple_distinct_postcondition_kind`].
    #[must_use]
    pub fn has_multiple_distinct_postcondition_kind(&self) -> bool {
        self.postconditions.has_multiple_distinct_kinds()
    }

    /// `true` iff `preconditions ∪ postconditions` carries AT MOST ONE
    /// [`ConditionKind::ALL`] variant — the union arm of the
    /// (precondition, postcondition, condition-union) cardinality
    /// "≤ 1" triad on [`Boundary`] closing the "at most one kind
    /// covered" arm on the union of the two condition slots on the
    /// closed-set-inversion axis. The Boolean cardinality "≤ 1"
    /// negation peer of [`Self::has_multiple_distinct_condition_kind`]
    /// (≥ 2 many-arm) under the definitional negation
    /// `!has_multiple_distinct_condition_kind`, and the trichotomy-
    /// union peer of `!has_any_distinct_condition_kind` (=0 empty-
    /// endpoint) OR [`Self::has_unique_distinct_condition_kind`] (=1
    /// mid-endpoint) — the arrangement space where the boundary is
    /// EMPTY-OR-SINGLETON on the union (zero or exactly one kind
    /// present across the union of the two slices).
    ///
    /// Composed body: `!self.has_multiple_distinct_condition_kind()` —
    /// a definitional negation of the many-arm union primitive. Short-
    /// circuits transitively through
    /// [`Self::has_multiple_distinct_condition_kind`]'s two-step
    /// short-circuit walk over [`ConditionKind::ALL`] under
    /// [`Self::has_condition_kind`] — returns `true` as soon as the
    /// many-arm walk stops with fewer than two distinct hits, WITHOUT
    /// materializing [`Self::distinct_condition_kinds`]'s `Vec` and
    /// WITHOUT walking every slot to build
    /// [`Self::distinct_condition_kind_count`]'s scalar. Byte-for-byte
    /// peer of [`ConditionSliceExt::has_at_most_one_distinct_kind`]
    /// one slice-layer down, lifted to compose against
    /// [`Self::has_condition_kind`]'s pre-OR-post union rather than
    /// against a single slice's `has_kind`. A regression at the union
    /// primitive fails at the slice-level substrate tests + the union
    /// composition-law tests rather than as silent drift here.
    ///
    /// # Peer on the ephemeral surface — [`crate::ephemeral::EphemeralSpec::has_at_most_one_distinct_condition_kind`]
    ///
    /// Byte-identical signature `(&Self) -> bool`, byte-identical
    /// definitional-negation body composed against the ephemeral
    /// surface's own many-arm union primitive. Both methods compose
    /// against the SAME slice-level substrate primitive
    /// [`ConditionSliceExt::has_at_most_one_distinct_kind`] via the
    /// two-slice union — a regression at the per-slice "≤ 1" negation
    /// fails at that primitive's tests rather than as silent drift at
    /// either struct-level empty-or-singleton caller.
    ///
    /// # Peer to [`Self::has_at_most_one_missing_condition_kind`]
    ///
    /// Axis-parity mirror of the closed-set-complement "≤ 1" negation
    /// peer on the union struct layer — where
    /// `has_at_most_one_missing_condition_kind` tests "at most one
    /// kind MISSING across the union" (near-saturation-or-saturated),
    /// this primitive tests "at most one kind PRESENT across the
    /// union" (empty-or-singleton). Both compose the same
    /// definitional negation shape (`!has_multiple_*_condition_kind()`)
    /// at the union struct layer — the two primitives close the "≤ 1"
    /// arm on both the closed-set-complement and closed-set-inversion
    /// axes at the union struct layer under the SAME shape.
    ///
    /// # Compounding
    ///
    /// A future operator-facing "at most one dependency currently
    /// covered" coverage-analysis diagnostic reads
    /// `boundary.has_at_most_one_distinct_condition_kind()` at ONE
    /// call site rather than restating
    /// `boundary.distinct_condition_kind_count() <= 1` (which walks
    /// every slot to count) or
    /// `boundary.distinct_condition_kinds().len() <= 1` (which
    /// allocates the Vec). A `has-at-most-one-distinct-condition-kind`
    /// require-tag classifier arm reaches this primitive at ONE
    /// substrate call — byte-for-byte peer of the tagged-union
    /// `has-at-most-one-populated-kind` classifier one struct-layer
    /// up, closing the {0, 1, ≥ 2, ≤ 1} cardinality-Boolean grid on
    /// the distinct axis at the Boundary struct layer alongside its
    /// sibling `has-multiple-distinct-condition-kind` under the
    /// Boolean negation axis.
    ///
    /// Theory anchor: THEORY.md §II.1 invariant 5 (composition
    /// preserves proofs — the cardinality "≤ 1" projection on the
    /// distinct axis composes the SAME definitional negation of the
    /// many-arm two-step short-circuit walk on both this boundary
    /// surface and the ephemeral surface). THEORY.md §VI.1 (generation
    /// over composition — a new [`ConditionKind`] variant reaches both
    /// surfaces' cardinality "≤ 1" triads mechanically through the
    /// delegated union primitive).
    #[must_use]
    pub fn has_at_most_one_distinct_condition_kind(&self) -> bool {
        !self.has_multiple_distinct_condition_kind()
    }

    /// `true` iff [`Self::preconditions`] carries AT MOST ONE
    /// [`ConditionKind::ALL`] variant — the precondition-side arm of
    /// the (precondition, postcondition, condition-union) cardinality
    /// "≤ 1" triad on [`Boundary`] on the closed-set-inversion axis.
    /// Thin typed delegate to
    /// [`ConditionSliceExt::has_at_most_one_distinct_kind`] over
    /// [`Self::preconditions`].
    ///
    /// Peer of [`Self::has_at_most_one_distinct_postcondition_kind`]
    /// on the (precondition, postcondition) partition of the boundary's
    /// two condition-vector slots; both peers compose against the SAME
    /// slice-level substrate primitive so a regression at the per-
    /// slice "≤ 1" negation of the many-arm walk fails at that
    /// primitive's tests rather than as silent drift at either
    /// struct-level arm.
    #[must_use]
    pub fn has_at_most_one_distinct_precondition_kind(&self) -> bool {
        self.preconditions.has_at_most_one_distinct_kind()
    }

    /// `true` iff [`Self::postconditions`] carries AT MOST ONE
    /// [`ConditionKind::ALL`] variant — the postcondition-side arm of
    /// the (precondition, postcondition, condition-union) cardinality
    /// "≤ 1" triad on [`Boundary`] on the closed-set-inversion axis.
    /// Thin typed delegate to
    /// [`ConditionSliceExt::has_at_most_one_distinct_kind`] over
    /// [`Self::postconditions`].
    ///
    /// Peer of [`Self::has_at_most_one_distinct_precondition_kind`].
    /// See that method for the full rationale — the two methods share
    /// ONE lift motivation, ONE fail-before-pass-after composition-
    /// law pin, and ONE two-surface parity contract with the
    /// ephemeral sugar type via
    /// [`crate::ephemeral::EphemeralSpec::has_at_most_one_distinct_postcondition_kind`].
    #[must_use]
    pub fn has_at_most_one_distinct_postcondition_kind(&self) -> bool {
        self.postconditions.has_at_most_one_distinct_kind()
    }

    /// `true` iff `preconditions ∪ postconditions` carries NO
    /// [`ConditionKind::ALL`] variant — the union arm of the
    /// (precondition, postcondition, condition-union) cardinality zero-
    /// endpoint triad on [`Boundary`] closing the "no kind covered"
    /// endpoint on the union of the two condition slots on the closed-
    /// set-inversion axis. The zero-endpoint Boolean fast-path peer of
    /// [`Self::has_any_distinct_condition_kind`] under a definitional
    /// negation, and the axis-parity mirror of
    /// [`Self::is_condition_kind_saturated`] on the closed-set-inversion
    /// axis at the union struct layer — where the saturation-endpoint
    /// predicate answers "does the union carry EVERY ALL variant?", this
    /// primitive answers "does the union carry NO ALL variant?".
    ///
    /// Composed body: `!self.has_any_distinct_condition_kind()` — a
    /// definitional negation of the at-least-one halfspace union
    /// primitive. Short-circuits transitively through
    /// [`Self::has_any_distinct_condition_kind`]'s short-circuiting
    /// closed-set walk over [`ConditionKind::ALL`] under
    /// [`Self::has_condition_kind`] — returns `false` at the FIRST
    /// present kind on either slice (yielding `false` here) WITHOUT
    /// materializing [`Self::distinct_condition_kinds`]'s `Vec` and
    /// WITHOUT walking every slot to build
    /// [`Self::distinct_condition_kind_count`]'s scalar. Byte-for-byte
    /// peer of [`ConditionSliceExt::is_kind_empty`] one slice-layer
    /// down, lifted to compose against [`Self::has_condition_kind`]'s
    /// pre-OR-post union rather than against a single slice's
    /// `has_kind`. A regression at the union primitive fails at the
    /// slice-level substrate tests + the union composition-law tests
    /// rather than as silent drift here.
    ///
    /// # Peer on the ephemeral surface — [`crate::ephemeral::EphemeralSpec::is_condition_kind_empty`]
    ///
    /// Byte-identical signature `(&Self) -> bool`, byte-identical
    /// definitional-negation body composed against the ephemeral
    /// surface's own at-least-one halfspace union primitive. Both
    /// methods compose against the SAME slice-level substrate primitive
    /// [`ConditionSliceExt::is_kind_empty`] via the two-slice union — a
    /// regression at the per-slice zero-endpoint fails at that
    /// primitive's tests rather than as silent drift at either
    /// struct-level empty caller.
    ///
    /// # Peer to [`Self::is_condition_kind_saturated`]
    ///
    /// Axis-parity mirror of the closed-set-complement saturation-
    /// endpoint peer on the union struct layer — where
    /// `is_condition_kind_saturated` tests "every kind PRESENT across
    /// the union" (missing_kind_count == 0), this primitive tests "no
    /// kind PRESENT across the union" (distinct_kind_count == 0). Both
    /// name a cardinality-endpoint on their respective axis under the
    /// same union struct layer — the two primitives close the zero-arm
    /// on both the closed-set-complement and closed-set-inversion axes
    /// at the union struct layer under symmetric shapes. Together with
    /// the intermediate arms `has_unique_distinct_condition_kind` (=1)
    /// and `has_multiple_distinct_condition_kind` (≥ 2), the four
    /// Booleans partition the distinct-cardinality closed set on the
    /// union at 0, 1, and ≥ 2 respectively.
    ///
    /// # Compounding
    ///
    /// A future operator-facing "no dependency currently covered"
    /// coverage-gap diagnostic reads
    /// `boundary.is_condition_kind_empty()` at ONE call site rather
    /// than restating `boundary.distinct_condition_kind_count() == 0`
    /// (which walks every slot to count),
    /// `boundary.distinct_condition_kinds().is_empty()` (which
    /// allocates the Vec), or negating
    /// `boundary.has_any_distinct_condition_kind()` at the callsite. An
    /// `is-condition-kind-empty` require-tag classifier arm reaches
    /// this primitive at ONE substrate call — byte-for-byte peer of
    /// the tagged-union `is-empty` classifier one struct-layer up,
    /// closing the {0, 1, ≥ 2, ≤ 1} cardinality-Boolean grid on the
    /// distinct axis at the Boundary struct layer alongside its sibling
    /// `has-any-distinct-condition-kind` under the Boolean negation
    /// axis.
    ///
    /// Theory anchor: THEORY.md §II.1 invariant 5 (composition
    /// preserves proofs — the cardinality zero-endpoint projection on
    /// the distinct axis composes the SAME definitional negation of
    /// the at-least-one halfspace short-circuit walk on both this
    /// boundary surface and the ephemeral surface). THEORY.md §VI.1
    /// (generation over composition — a new [`ConditionKind`] variant
    /// reaches both surfaces' cardinality zero-endpoint triads
    /// mechanically through the delegated union primitive).
    #[must_use]
    pub fn is_condition_kind_empty(&self) -> bool {
        !self.has_any_distinct_condition_kind()
    }

    /// `true` iff [`Self::preconditions`] carries NO
    /// [`ConditionKind::ALL`] variant — the precondition-side arm of
    /// the (precondition, postcondition, condition-union) cardinality
    /// zero-endpoint triad on [`Boundary`] on the closed-set-inversion
    /// axis. Thin typed delegate to [`ConditionSliceExt::is_kind_empty`]
    /// over [`Self::preconditions`].
    ///
    /// Peer of [`Self::is_postcondition_kind_empty`] on the
    /// (precondition, postcondition) partition of the boundary's two
    /// condition-vector slots; both peers compose against the SAME
    /// slice-level substrate primitive so a regression at the per-slice
    /// zero-endpoint short-circuit fails at that primitive's tests
    /// rather than as silent drift at either struct-level arm.
    #[must_use]
    pub fn is_precondition_kind_empty(&self) -> bool {
        self.preconditions.is_kind_empty()
    }

    /// `true` iff [`Self::postconditions`] carries NO
    /// [`ConditionKind::ALL`] variant — the postcondition-side arm of
    /// the (precondition, postcondition, condition-union) cardinality
    /// zero-endpoint triad on [`Boundary`] on the closed-set-inversion
    /// axis. Thin typed delegate to [`ConditionSliceExt::is_kind_empty`]
    /// over [`Self::postconditions`].
    ///
    /// Peer of [`Self::is_precondition_kind_empty`]. See that method
    /// for the full rationale — the two methods share ONE lift
    /// motivation, ONE fail-before-pass-after composition-law pin, and
    /// ONE two-surface parity contract with the ephemeral sugar type
    /// via
    /// [`crate::ephemeral::EphemeralSpec::is_postcondition_kind_empty`].
    #[must_use]
    pub fn is_postcondition_kind_empty(&self) -> bool {
        self.postconditions.is_kind_empty()
    }

    /// `true` iff `preconditions ∪ postconditions` carries AT LEAST ONE
    /// [`ConditionKind::ALL`] variant AND is MISSING AT LEAST ONE
    /// [`ConditionKind::ALL`] variant — the union arm of the
    /// (precondition, postcondition, condition-union) parent-state
    /// middle-arm triad on [`Boundary`] closing the trichotomy
    /// (empty, partially covered, saturated) on the union axis
    /// alongside [`Self::is_condition_kind_empty`] (=0 zero-endpoint on
    /// the distinct axis) and [`Self::is_condition_kind_saturated`]
    /// (=0 zero-endpoint on the missing axis).
    ///
    /// # Composed body
    ///
    /// `self.has_any_distinct_condition_kind() && self.has_any_missing_condition_kind()`
    /// — the paired at-least-one-halfspace composition. Short-circuits
    /// transitively through the two at-least-one halfspace union
    /// primitives, each of which walks
    /// `ConditionKind::ALL.iter().any(has_condition_kind)` under a
    /// polarity — WITHOUT materializing
    /// [`Self::distinct_condition_kinds`] or
    /// [`Self::missing_condition_kinds`]'s `Vec`s and WITHOUT walking
    /// every slot to build the paired scalar counters. Byte-for-byte
    /// cheaper than the widened negation-of-both-endpoints composition
    /// `!self.is_condition_kind_empty() && !self.is_condition_kind_saturated()`
    /// on every partially-covered arm because each halfspace short-
    /// circuits at the first present / missing hit rather than paying
    /// two separate `ALL`-length walks.
    ///
    /// # Peer on the ephemeral surface — [`crate::ephemeral::EphemeralSpec::is_condition_kind_partially_covered`]
    ///
    /// Byte-identical signature `(&Self) -> bool`, byte-identical
    /// paired-halfspace body, on the sugar-surface type whose pre/post
    /// condition vectors live directly on the struct. Both methods
    /// compose against the SAME slice-level substrate primitive
    /// [`ConditionSliceExt::is_kind_partially_covered`] via the
    /// two-slice union composed through
    /// [`Self::has_condition_kind`] — a regression at the per-slice
    /// fused short-circuit walk fails at that primitive's tests rather
    /// than as silent drift at either struct-level middle-arm caller.
    ///
    /// # Compounding
    ///
    /// A boundary-progress "some kinds covered, some pending"
    /// diagnostic on a Boundary reads
    /// `boundary.is_condition_kind_partially_covered()` at ONE call
    /// site rather than composing
    /// `!boundary.is_condition_kind_empty() && !boundary.is_condition_kind_saturated()`
    /// (two closed-set walks) or
    /// `boundary.distinct_condition_kind_count() > 0 && boundary.missing_condition_kind_count() > 0`
    /// (two counter walks with no short-circuit). An `is-condition-
    /// kind-partially-covered` require-tag classifier arm reaches this
    /// primitive at ONE substrate call — byte-for-byte peer of the
    /// tagged-union `is-partially-populated` classifier one struct-
    /// layer up under the SAME parent-state middle-arm shape.
    ///
    /// Theory anchor: THEORY.md §II.1 invariant 5 (composition
    /// preserves proofs — the parent-state middle-arm projection
    /// composes the SAME paired-halfspace body on both this boundary
    /// surface and the ephemeral surface). THEORY.md §VI.1 (generation
    /// over composition — a new [`ConditionKind`] variant reaches both
    /// surfaces' parent-state middle-arm triads mechanically through
    /// the delegated union primitive).
    #[must_use]
    pub fn is_condition_kind_partially_covered(&self) -> bool {
        self.has_any_distinct_condition_kind() && self.has_any_missing_condition_kind()
    }

    /// `true` iff [`Self::preconditions`] carries AT LEAST ONE
    /// [`ConditionKind::ALL`] variant AND is MISSING AT LEAST ONE
    /// [`ConditionKind::ALL`] variant — the precondition-side arm of
    /// the (precondition, postcondition, condition-union) parent-state
    /// middle-arm triad on [`Boundary`]. Thin typed delegate to
    /// [`ConditionSliceExt::is_kind_partially_covered`] over
    /// [`Self::preconditions`].
    ///
    /// Peer of [`Self::is_postcondition_kind_partially_covered`] on the
    /// (precondition, postcondition) partition of the boundary's two
    /// condition-vector slots; both peers compose against the SAME
    /// slice-level substrate primitive so a regression at the per-slice
    /// fused short-circuit walk fails at that primitive's tests rather
    /// than as silent drift at either struct-level arm.
    #[must_use]
    pub fn is_precondition_kind_partially_covered(&self) -> bool {
        self.preconditions.is_kind_partially_covered()
    }

    /// `true` iff [`Self::postconditions`] carries AT LEAST ONE
    /// [`ConditionKind::ALL`] variant AND is MISSING AT LEAST ONE
    /// [`ConditionKind::ALL`] variant — the postcondition-side arm of
    /// the (precondition, postcondition, condition-union) parent-state
    /// middle-arm triad on [`Boundary`]. Thin typed delegate to
    /// [`ConditionSliceExt::is_kind_partially_covered`] over
    /// [`Self::postconditions`].
    ///
    /// Peer of [`Self::is_precondition_kind_partially_covered`]. See
    /// that method for the full rationale — the two methods share ONE
    /// lift motivation, ONE fail-before-pass-after composition-law pin,
    /// and ONE two-surface parity contract with the ephemeral sugar
    /// type via
    /// [`crate::ephemeral::EphemeralSpec::is_postcondition_kind_partially_covered`].
    #[must_use]
    pub fn is_postcondition_kind_partially_covered(&self) -> bool {
        self.postconditions.is_kind_partially_covered()
    }

    /// `true` iff `preconditions ∪ postconditions` is MISSING EXACTLY
    /// ONE [`ConditionKind::ALL`] variant — the union arm of the
    /// (precondition, postcondition, condition-union) cardinality-mid-
    /// endpoint triad on [`Boundary`] closing the "one hole remaining"
    /// near-saturation-endpoint on the union of the two condition
    /// slots. The near-saturation-endpoint Boolean fast-path peer of
    /// [`Self::is_condition_kind_saturated`] on the union axis: where
    /// the saturation-endpoint predicate answers "is the union covered
    /// by every ALL variant?", `has_unique_missing_condition_kind`
    /// answers "is the union one kind away from covered?".
    ///
    /// Composed body: constructs a two-step-short-circuit walk over
    /// [`ConditionKind::ALL`] under the [`Self::has_condition_kind`]
    /// union primitive negated — the first missing union arm surfaces,
    /// then the walk short-circuits at the second. Byte-for-byte peer
    /// of [`ConditionSliceExt::has_unique_missing_kind`] one slice-
    /// layer down, lifted to compose against
    /// [`Self::has_condition_kind`]'s pre-OR-post union rather than
    /// against a single slice's `has_kind`. A regression at the union
    /// primitive fails at the slice-level substrate tests + the union
    /// composition-law tests rather than as silent drift here.
    ///
    /// # Peer on the ephemeral surface — [`crate::ephemeral::EphemeralSpec::has_unique_missing_condition_kind`]
    ///
    /// Byte-identical signature `(&Self) -> bool`, byte-identical
    /// two-step short-circuit body composed against the ephemeral
    /// surface's own union primitive. Both methods compose against
    /// the SAME slice-level substrate primitive
    /// [`ConditionSliceExt::has_unique_missing_kind`] via the two-
    /// slice union — a regression at the per-slice near-saturation-
    /// endpoint walk fails at that primitive's tests rather than as
    /// silent drift at either struct-level near-saturation caller.
    ///
    /// # Compounding
    ///
    /// A future operator-facing "one kind away from saturated" gap-
    /// analysis diagnostic reads
    /// `boundary.has_unique_missing_condition_kind()` at ONE call site
    /// rather than restating either `boundary.missing_condition_kind_count() == 1`
    /// (which walks every slot to count) or
    /// `boundary.missing_condition_kinds().len() == 1` (which
    /// allocates the Vec). A `has-unique-missing-condition-kind`
    /// require-tag classifier arm reaches this primitive at ONE
    /// substrate call — byte-for-byte peer of the tagged-union
    /// `has-unique-missing-kind` classifier one struct-layer up.
    ///
    /// Theory anchor: THEORY.md §II.1 invariant 5 (composition
    /// preserves proofs — the cardinality-mid-endpoint projection on
    /// the missing axis composes the SAME two-step short-circuit walk
    /// under a two-slice union negation on both this boundary surface
    /// and the ephemeral surface). THEORY.md §VI.1 (generation over
    /// composition — a new [`ConditionKind`] variant reaches both
    /// surfaces' cardinality-mid-endpoint triads mechanically through
    /// the delegated union primitive).
    #[must_use]
    pub fn has_unique_missing_condition_kind(&self) -> bool {
        let mut it = ConditionKind::ALL
            .iter()
            .copied()
            .filter(|k| !self.has_condition_kind(*k));
        it.next().is_some() && it.next().is_none()
    }

    /// `true` iff [`Self::preconditions`] is MISSING EXACTLY ONE
    /// [`ConditionKind::ALL`] variant — the precondition-side arm of
    /// the (precondition, postcondition, condition-union) cardinality-
    /// mid-endpoint triad on [`Boundary`]. Thin typed delegate to
    /// [`ConditionSliceExt::has_unique_missing_kind`] over
    /// [`Self::preconditions`].
    ///
    /// Peer of [`Self::has_unique_missing_postcondition_kind`] on the
    /// (precondition, postcondition) partition of the boundary's two
    /// condition-vector slots; both peers compose against the SAME
    /// slice-level substrate primitive so a regression at the per-
    /// slice two-step short-circuit walk under negation fails at that
    /// primitive's tests rather than as silent drift at either
    /// struct-level arm.
    #[must_use]
    pub fn has_unique_missing_precondition_kind(&self) -> bool {
        self.preconditions.has_unique_missing_kind()
    }

    /// `true` iff [`Self::postconditions`] is MISSING EXACTLY ONE
    /// [`ConditionKind::ALL`] variant — the postcondition-side arm of
    /// the (precondition, postcondition, condition-union) cardinality-
    /// mid-endpoint triad on [`Boundary`]. Thin typed delegate to
    /// [`ConditionSliceExt::has_unique_missing_kind`] over
    /// [`Self::postconditions`].
    ///
    /// Peer of [`Self::has_unique_missing_precondition_kind`]. See
    /// that method for the full rationale — the two methods share ONE
    /// lift motivation, ONE fail-before-pass-after composition-law
    /// pin, and ONE two-surface parity contract with the ephemeral
    /// sugar type via
    /// [`crate::ephemeral::EphemeralSpec::has_unique_missing_postcondition_kind`].
    #[must_use]
    pub fn has_unique_missing_postcondition_kind(&self) -> bool {
        self.postconditions.has_unique_missing_kind()
    }

    /// The SOLE [`ConditionKind::ALL`] variant ABSENT from
    /// `preconditions ∪ postconditions`, or `None` when the union is
    /// missing 0 or ≥ 2 kinds — the union arm of the (precondition,
    /// postcondition, condition-union) exactly-one-missing witnessing
    /// triad on [`Boundary`] closing the near-saturation witness on
    /// the closed-set-complement axis on the union of the two
    /// condition slots. Witnessing scalar peer of
    /// [`Self::has_unique_missing_condition_kind`] (=1 predicate) on
    /// the union axis: where the Boolean predicate answers "is the
    /// union one kind AWAY from covered?", `unique_missing_condition_kind`
    /// returns `Some(k)` naming that SOLE remaining hole (or `None` on
    /// the 0 or ≥ 2 arms).
    ///
    /// # Composed body
    ///
    /// A two-step-short-circuit walk over [`ConditionKind::ALL`] under
    /// a NEGATED [`Self::has_condition_kind`] union primitive — pull
    /// the first hit; return `Some(first)` iff the second hit is
    /// [`None`], else `None`. Byte-for-byte peer of
    /// [`ConditionSliceExt::unique_missing_kind`] one slice-layer
    /// down, lifted to compose against the two-slice union rather than
    /// against a single slice's `has_kind`. A regression at the union
    /// primitive fails at the slice-level substrate tests + the union
    /// composition-law tests rather than as silent drift here.
    ///
    /// # Peer on the ephemeral surface — [`crate::ephemeral::EphemeralSpec::unique_missing_condition_kind`]
    ///
    /// Byte-identical signature `(&Self) -> Option<ConditionKind>`,
    /// byte-identical two-step short-circuit body composed against the
    /// ephemeral surface's own union primitive. Both methods compose
    /// against the SAME slice-level substrate primitive
    /// [`ConditionSliceExt::unique_missing_kind`] via the two-slice
    /// union — a regression at the per-slice near-saturation
    /// witnessing walk fails at that primitive's tests rather than as
    /// silent drift at either struct-level near-saturation caller.
    ///
    /// # Sibling to [`Self::unique_distinct_condition_kind`]
    ///
    /// Closed-set-complement peer of the exactly-one-hit witness on
    /// the closed-set-inversion axis at the boundary union struct
    /// layer — where `unique_distinct_condition_kind` names the SOLE
    /// kind COVERED, `unique_missing_condition_kind` names the SOLE
    /// kind ABSENT. Both compose against a two-step-short-circuit walk
    /// over [`ConditionKind::ALL`] under [`Self::has_condition_kind`]
    /// vs `!has_condition_kind` (this primitive).
    ///
    /// # Compounding
    ///
    /// A future gap-analysis diagnostic that names "one remaining
    /// [`ConditionKind`] not covered by this Boundary" reads
    /// `boundary.unique_missing_condition_kind()` at ONE call site —
    /// the WITNESS + the exactly-one predicate composed at ONE short-
    /// circuit walk, rather than pairing the Boolean
    /// [`Self::has_unique_missing_condition_kind`] with
    /// [`Self::first_missing_condition_kind`] at TWO independent walks
    /// whose agreement is a coincidence.
    ///
    /// Theory anchor: THEORY.md §II.1 invariant 5 (composition
    /// preserves proofs — the complement-exactly-one-hit witnessing
    /// projection composes the SAME two-step short-circuit walk under
    /// a two-slice union negation on both this boundary surface and
    /// the ephemeral surface). THEORY.md §VI.1 (generation over
    /// composition — a new [`ConditionKind`] variant reaches both
    /// surfaces' unique-missing-kind triads mechanically through the
    /// delegated union primitive).
    #[must_use]
    pub fn unique_missing_condition_kind(&self) -> Option<ConditionKind> {
        let mut it = ConditionKind::ALL
            .iter()
            .copied()
            .filter(|k| !self.has_condition_kind(*k));
        let first = it.next()?;
        match it.next() {
            None => Some(first),
            Some(_) => None,
        }
    }

    /// The SOLE [`ConditionKind::ALL`] variant ABSENT from
    /// [`Self::preconditions`], or `None` when preconditions are
    /// missing 0 or ≥ 2 kinds — the precondition-side arm of the
    /// (precondition, postcondition, condition-union) exactly-one-
    /// missing witnessing triad on [`Boundary`]. Thin typed delegate
    /// to [`ConditionSliceExt::unique_missing_kind`] over
    /// [`Self::preconditions`].
    ///
    /// Peer of [`Self::unique_missing_postcondition_kind`] on the
    /// (precondition, postcondition) partition of the boundary's two
    /// condition-vector slots; both peers compose against the SAME
    /// slice-level substrate primitive so a regression at the per-
    /// slice two-step short-circuit witnessing walk under negation
    /// fails at that primitive's tests rather than as silent drift at
    /// either struct-level arm.
    #[must_use]
    pub fn unique_missing_precondition_kind(&self) -> Option<ConditionKind> {
        self.preconditions.unique_missing_kind()
    }

    /// The SOLE [`ConditionKind::ALL`] variant ABSENT from
    /// [`Self::postconditions`], or `None` when postconditions are
    /// missing 0 or ≥ 2 kinds — the postcondition-side arm of the
    /// (precondition, postcondition, condition-union) exactly-one-
    /// missing witnessing triad on [`Boundary`]. Thin typed delegate
    /// to [`ConditionSliceExt::unique_missing_kind`] over
    /// [`Self::postconditions`].
    ///
    /// Peer of [`Self::unique_missing_precondition_kind`]. See that
    /// method for the full rationale — the two methods share ONE lift
    /// motivation, ONE fail-before-pass-after composition-law pin, and
    /// ONE two-surface parity contract with the ephemeral sugar type
    /// via
    /// [`crate::ephemeral::EphemeralSpec::unique_missing_postcondition_kind`].
    #[must_use]
    pub fn unique_missing_postcondition_kind(&self) -> Option<ConditionKind> {
        self.postconditions.unique_missing_kind()
    }

    /// `true` iff `preconditions ∪ postconditions` is MISSING AT
    /// LEAST TWO [`ConditionKind::ALL`] variants — the union arm of
    /// the (precondition, postcondition, condition-union) cardinality-
    /// many-arm triad on [`Boundary`] closing the "≥ 2 holes
    /// remaining" arm on the union of the two condition slots. The
    /// many-arm Boolean fast-path peer of
    /// [`Self::has_unique_missing_condition_kind`] (=1 arm) and
    /// [`Self::is_condition_kind_saturated`] (=0 arm) on the union
    /// axis, closing the {0, 1, ≥2} trichotomy at the union struct
    /// layer.
    ///
    /// Composed body: constructs a two-step-short-circuit walk over
    /// [`ConditionKind::ALL`] under the [`Self::has_condition_kind`]
    /// union primitive negated — pulls up to two hits off the
    /// filtered iterator; the primitive returns `true` iff BOTH the
    /// first and the second are [`Some`]. Byte-for-byte peer of
    /// [`ConditionSliceExt::has_multiple_missing_kinds`] one slice-
    /// layer down, lifted to compose against
    /// [`Self::has_condition_kind`]'s pre-OR-post union rather than
    /// against a single slice's `has_kind`. A regression at the union
    /// primitive fails at the slice-level substrate tests + the union
    /// composition-law tests rather than as silent drift here.
    ///
    /// # Peer on the ephemeral surface — [`crate::ephemeral::EphemeralSpec::has_multiple_missing_condition_kind`]
    ///
    /// Byte-identical signature `(&Self) -> bool`, byte-identical
    /// two-step short-circuit body composed against the ephemeral
    /// surface's own union primitive. Both methods compose against
    /// the SAME slice-level substrate primitive
    /// [`ConditionSliceExt::has_multiple_missing_kinds`] via the two-
    /// slice union — a regression at the per-slice many-arm walk
    /// fails at that primitive's tests rather than as silent drift at
    /// either struct-level many-missing caller.
    ///
    /// # Compounding
    ///
    /// A future operator-facing "≥ 2 dependencies still unfulfilled"
    /// gap-analysis diagnostic reads
    /// `boundary.has_multiple_missing_condition_kind()` at ONE call
    /// site rather than restating
    /// `boundary.missing_condition_kind_count() >= 2` (which walks
    /// every slot to count) or
    /// `boundary.missing_condition_kinds().len() >= 2` (which
    /// allocates the Vec). A `has-multiple-missing-condition-kind`
    /// require-tag classifier arm reaches this primitive at ONE
    /// substrate call — byte-for-byte peer of the tagged-union
    /// `has-multiple-missing-kinds` classifier one struct-layer up.
    ///
    /// Theory anchor: THEORY.md §II.1 invariant 5 (composition
    /// preserves proofs — the cardinality-many-arm projection on the
    /// missing axis composes the SAME two-step short-circuit walk
    /// under a two-slice union negation on both this boundary surface
    /// and the ephemeral surface). THEORY.md §VI.1 (generation over
    /// composition — a new [`ConditionKind`] variant reaches both
    /// surfaces' cardinality-many-arm triads mechanically through the
    /// delegated union primitive).
    #[must_use]
    pub fn has_multiple_missing_condition_kind(&self) -> bool {
        let mut it = ConditionKind::ALL
            .iter()
            .copied()
            .filter(|k| !self.has_condition_kind(*k));
        it.next().is_some() && it.next().is_some()
    }

    /// `true` iff [`Self::preconditions`] is MISSING AT LEAST TWO
    /// [`ConditionKind::ALL`] variants — the precondition-side arm of
    /// the (precondition, postcondition, condition-union) cardinality-
    /// many-arm triad on [`Boundary`]. Thin typed delegate to
    /// [`ConditionSliceExt::has_multiple_missing_kinds`] over
    /// [`Self::preconditions`].
    ///
    /// Peer of [`Self::has_multiple_missing_postcondition_kind`] on
    /// the (precondition, postcondition) partition of the boundary's
    /// two condition-vector slots; both peers compose against the
    /// SAME slice-level substrate primitive so a regression at the
    /// per-slice two-step short-circuit walk under negation fails at
    /// that primitive's tests rather than as silent drift at either
    /// struct-level arm.
    #[must_use]
    pub fn has_multiple_missing_precondition_kind(&self) -> bool {
        self.preconditions.has_multiple_missing_kinds()
    }

    /// `true` iff [`Self::postconditions`] is MISSING AT LEAST TWO
    /// [`ConditionKind::ALL`] variants — the postcondition-side arm of
    /// the (precondition, postcondition, condition-union) cardinality-
    /// many-arm triad on [`Boundary`]. Thin typed delegate to
    /// [`ConditionSliceExt::has_multiple_missing_kinds`] over
    /// [`Self::postconditions`].
    ///
    /// Peer of [`Self::has_multiple_missing_precondition_kind`]. See
    /// that method for the full rationale — the two methods share ONE
    /// lift motivation, ONE fail-before-pass-after composition-law
    /// pin, and ONE two-surface parity contract with the ephemeral
    /// sugar type via
    /// [`crate::ephemeral::EphemeralSpec::has_multiple_missing_postcondition_kind`].
    #[must_use]
    pub fn has_multiple_missing_postcondition_kind(&self) -> bool {
        self.postconditions.has_multiple_missing_kinds()
    }

    /// `true` iff `preconditions ∪ postconditions` is MISSING AT MOST
    /// ONE [`ConditionKind::ALL`] variant — the union arm of the
    /// (precondition, postcondition, condition-union) cardinality
    /// "≤ 1" triad on [`Boundary`] closing the "at most one hole
    /// remaining" arm on the union of the two condition slots. The
    /// Boolean cardinality "≤ 1" negation peer of
    /// [`Self::has_multiple_missing_condition_kind`] (≥ 2 many-arm)
    /// under the definitional negation
    /// `!has_multiple_missing_condition_kind`, and the trichotomy-
    /// union peer of [`Self::is_condition_kind_saturated`] (=0
    /// zero-arm) OR [`Self::has_unique_missing_condition_kind`] (=1
    /// mid-endpoint) — the arrangement space where the boundary is
    /// SATURATED-OR-NEAR-SATURATED (zero or exactly one kind missing
    /// across the union of the two slices).
    ///
    /// Composed body: `!self.has_multiple_missing_condition_kind()` —
    /// a definitional negation of the many-arm union primitive. Short-
    /// circuits transitively through
    /// [`Self::has_multiple_missing_condition_kind`]'s two-step short-
    /// circuit walk over [`ConditionKind::ALL`] under negated
    /// [`Self::has_condition_kind`] — returns `true` as soon as the
    /// many-arm walk stops with fewer than two missing hits, WITHOUT
    /// materializing [`Self::missing_condition_kinds`]'s `Vec` and
    /// WITHOUT walking every slot to build
    /// [`Self::missing_condition_kind_count`]'s scalar. Byte-for-byte
    /// peer of [`ConditionSliceExt::has_at_most_one_missing_kind`] one
    /// slice-layer down, lifted to compose against
    /// [`Self::has_condition_kind`]'s pre-OR-post union rather than
    /// against a single slice's `has_kind`. A regression at the union
    /// primitive fails at the slice-level substrate tests + the union
    /// composition-law tests rather than as silent drift here.
    ///
    /// # Peer on the ephemeral surface — [`crate::ephemeral::EphemeralSpec::has_at_most_one_missing_condition_kind`]
    ///
    /// Byte-identical signature `(&Self) -> bool`, byte-identical
    /// definitional-negation body composed against the ephemeral
    /// surface's own many-arm union primitive. Both methods compose
    /// against the SAME slice-level substrate primitive
    /// [`ConditionSliceExt::has_at_most_one_missing_kind`] via the
    /// two-slice union — a regression at the per-slice "≤ 1" negation
    /// fails at that primitive's tests rather than as silent drift at
    /// either struct-level near-saturation-or-saturated caller.
    ///
    /// # Compounding
    ///
    /// A future operator-facing "at most one dependency still
    /// unfulfilled" gap-analysis diagnostic reads
    /// `boundary.has_at_most_one_missing_condition_kind()` at ONE call
    /// site rather than restating
    /// `boundary.missing_condition_kind_count() <= 1` (which walks every
    /// slot to count) or `boundary.missing_condition_kinds().len() <= 1`
    /// (which allocates the Vec) or the union of the two Booleans
    /// `boundary.is_condition_kind_saturated() ||
    /// boundary.has_unique_missing_condition_kind()` (which walks the
    /// closed-set-complement scan twice). A `has-at-most-one-missing-
    /// condition-kind` require-tag classifier arm reaches this
    /// primitive at ONE substrate call — byte-for-byte peer of the
    /// tagged-union `has-at-most-one-missing-kind` classifier one
    /// struct-layer up, closing the {0, 1, ≥ 2, ≤ 1} cardinality-
    /// Boolean grid on the missing axis at the Boundary struct layer
    /// alongside its sibling `has-multiple-missing-condition-kind`
    /// under the Boolean negation axis.
    ///
    /// Theory anchor: THEORY.md §II.1 invariant 5 (composition
    /// preserves proofs — the cardinality "≤ 1" projection on the
    /// missing axis composes the SAME definitional negation of the
    /// many-arm two-step short-circuit walk on both this boundary
    /// surface and the ephemeral surface). THEORY.md §VI.1 (generation
    /// over composition — a new [`ConditionKind`] variant reaches both
    /// surfaces' cardinality "≤ 1" triads mechanically through the
    /// delegated union primitive).
    #[must_use]
    pub fn has_at_most_one_missing_condition_kind(&self) -> bool {
        !self.has_multiple_missing_condition_kind()
    }

    /// `true` iff [`Self::preconditions`] is MISSING AT MOST ONE
    /// [`ConditionKind::ALL`] variant — the precondition-side arm of
    /// the (precondition, postcondition, condition-union) cardinality
    /// "≤ 1" triad on [`Boundary`]. Thin typed delegate to
    /// [`ConditionSliceExt::has_at_most_one_missing_kind`] over
    /// [`Self::preconditions`].
    ///
    /// Peer of [`Self::has_at_most_one_missing_postcondition_kind`]
    /// on the (precondition, postcondition) partition of the boundary's
    /// two condition-vector slots; both peers compose against the SAME
    /// slice-level substrate primitive so a regression at the per-
    /// slice "≤ 1" negation of the many-arm walk fails at that
    /// primitive's tests rather than as silent drift at either
    /// struct-level arm.
    #[must_use]
    pub fn has_at_most_one_missing_precondition_kind(&self) -> bool {
        self.preconditions.has_at_most_one_missing_kind()
    }

    /// `true` iff [`Self::postconditions`] is MISSING AT MOST ONE
    /// [`ConditionKind::ALL`] variant — the postcondition-side arm of
    /// the (precondition, postcondition, condition-union) cardinality
    /// "≤ 1" triad on [`Boundary`]. Thin typed delegate to
    /// [`ConditionSliceExt::has_at_most_one_missing_kind`] over
    /// [`Self::postconditions`].
    ///
    /// Peer of [`Self::has_at_most_one_missing_precondition_kind`].
    /// See that method for the full rationale — the two methods share
    /// ONE lift motivation, ONE fail-before-pass-after composition-
    /// law pin, and ONE two-surface parity contract with the
    /// ephemeral sugar type via
    /// [`crate::ephemeral::EphemeralSpec::has_at_most_one_missing_postcondition_kind`].
    #[must_use]
    pub fn has_at_most_one_missing_postcondition_kind(&self) -> bool {
        self.postconditions.has_at_most_one_missing_kind()
    }

    /// `true` iff `preconditions ∪ postconditions` carries NO
    /// [`Condition`] with the given [`ConditionKind`] — the union arm
    /// of the (precondition, postcondition, condition-union)
    /// per-kind-complement triad on [`Boundary`], definitional
    /// negation of [`Self::has_condition_kind`].
    ///
    /// # Composed body
    ///
    /// `!self.has_condition_kind(kind)` — the definitional negation
    /// of the two-slice union primitive. Equivalent to the AND of the
    /// two half-slice per-kind-complement arms
    /// (`self.lacks_precondition_kind(k) && self.lacks_postcondition_kind(k)`),
    /// by the boolean identity `!(a || b) == !a && !b`. Both forms
    /// return `true` iff BOTH slices lack the addressed kind; the
    /// composed body chosen here short-circuits through the union
    /// primitive so a regression at the per-slice presence probe fails
    /// at that primitive's tests rather than as silent drift at either
    /// half-slice complement arm. Equivalent to
    /// `self.missing_condition_kinds().contains(&kind)` without
    /// materializing the closed-set-complement Vec at every callsite.
    ///
    /// # Peer on the ephemeral surface — [`crate::ephemeral::EphemeralSpec::lacks_condition_kind`]
    ///
    /// Byte-identical signature `(&Self, ConditionKind) -> bool`,
    /// byte-identical `!self.has_condition_kind(kind)` body, on the
    /// sugar-surface type whose pre/post condition vectors live
    /// directly on the struct. Both methods compose against the SAME
    /// slice-level substrate primitive
    /// [`ConditionSliceExt::lacks_kind`] via the two-slice union
    /// composed through [`Self::has_condition_kind`] — a regression
    /// at the per-slice negation fails at that primitive's tests
    /// rather than as silent drift at either struct-level complement
    /// caller.
    ///
    /// # Compounding
    ///
    /// A `lacks-<kind>` require-tag classifier arm — byte-for-byte
    /// peer of the tagged-union `lacks-<kind>` classifier one struct-
    /// layer up + the future `condition-<kind>` require-tag family's
    /// negated dual — reaches this primitive at ONE call site rather
    /// than negating `boundary.has_condition_kind(k)` at the callsite
    /// or restating `boundary.missing_condition_kinds().contains(&k)`
    /// with its allocation.
    ///
    /// Theory anchor: THEORY.md §II.1 invariant 5 (composition
    /// preserves proofs — the per-kind closed-set-complement
    /// projection composes the SAME two-slice union negation on both
    /// this boundary surface and the slice-level substrate primitive
    /// under definitional negation). THEORY.md §VI.1 (generation over
    /// composition — a new [`ConditionKind`] variant reaches both
    /// surfaces' complement-triads mechanically through the delegated
    /// union primitive).
    #[must_use]
    pub fn lacks_condition_kind(&self, kind: ConditionKind) -> bool {
        !self.has_condition_kind(kind)
    }

    /// `true` iff [`Self::preconditions`] carries NO [`Condition`]
    /// with the given [`ConditionKind`] — the precondition-side arm
    /// of the (precondition, postcondition, condition-union)
    /// per-kind-complement triad on [`Boundary`]. Thin typed delegate
    /// to [`ConditionSliceExt::lacks_kind`] over
    /// [`Self::preconditions`].
    ///
    /// Peer of [`Self::lacks_postcondition_kind`] on the (precondition,
    /// postcondition) partition of the boundary's two condition-vector
    /// slots; both peers compose against the SAME slice-level substrate
    /// primitive so a regression at the per-slice negation fails at
    /// that primitive's tests rather than as silent drift at either
    /// struct-level arm.
    #[must_use]
    pub fn lacks_precondition_kind(&self, kind: ConditionKind) -> bool {
        self.preconditions.lacks_kind(kind)
    }

    /// `true` iff [`Self::postconditions`] carries NO [`Condition`]
    /// with the given [`ConditionKind`] — the postcondition-side arm
    /// of the (precondition, postcondition, condition-union)
    /// per-kind-complement triad on [`Boundary`]. Thin typed delegate
    /// to [`ConditionSliceExt::lacks_kind`] over
    /// [`Self::postconditions`].
    ///
    /// Peer of [`Self::lacks_precondition_kind`]. See that method for
    /// the full rationale — the two methods share ONE lift motivation,
    /// ONE fail-before-pass-after composition-law pin, and ONE
    /// two-surface parity contract with the ephemeral sugar type via
    /// [`crate::ephemeral::EphemeralSpec::lacks_postcondition_kind`].
    #[must_use]
    pub fn lacks_postcondition_kind(&self, kind: ConditionKind) -> bool {
        self.postconditions.lacks_kind(kind)
    }

    /// `true` iff `preconditions ∪ postconditions` carries at least
    /// one [`Condition`] with the given [`ConditionKind`] AND carries
    /// no [`Condition`] whose kind is anything OTHER than `kind` — the
    /// union arm of the (precondition, postcondition, condition-union)
    /// kind-scoped strict-refinement triad on [`Boundary`], byte-for-
    /// byte peer of the per-kind presence probe
    /// [`Self::has_condition_kind`] under the well-formed-diagonal
    /// refinement.
    ///
    /// # Composed body
    ///
    /// A FUSED short-circuit closed-set walk over
    /// [`ConditionKind::ALL`] under [`Self::has_condition_kind`] that
    /// returns `false` at the EARLIEST kind whose presence spans
    /// either slice's populated set and is NOT `kind`, and returns
    /// `true` iff the sweep completes with `kind` seen as the sole
    /// distinct populated kind. Strictly cheaper than the widened
    /// composition
    /// `boundary.distinct_condition_kinds() == vec![kind]` (which
    /// allocates the distinct-kind Vec before the equality test) or
    /// the (pre, post) AND-of-strict-refinement
    /// `boundary.preconditions.has_only_kind(kind)
    ///     && boundary.postconditions.has_only_kind(kind)` (which is
    /// TOO STRICT — a single-slice-populated arrangement whose empty
    /// side returns `false` fails this AND but IS well-formed on the
    /// union).
    ///
    /// # Peer on the ephemeral surface — [`crate::ephemeral::EphemeralSpec::has_only_condition_kind`]
    ///
    /// Byte-identical signature `(&Self, ConditionKind) -> bool`,
    /// byte-identical fused-closed-set-walk body, on the sugar-surface
    /// type whose pre/post condition vectors live directly on the
    /// struct. Both methods compose against the SAME slice-level
    /// substrate primitive [`ConditionSliceExt::has_only_kind`] via
    /// the two-slice union composed through
    /// [`Self::has_condition_kind`] — a regression at the per-slice
    /// fused walk fails at that primitive's tests rather than as
    /// silent drift at either struct-level kind-scoped-strict-
    /// refinement caller.
    ///
    /// # Compounding
    ///
    /// A future coherence check verifying "every attested closed-loop
    /// probe Process carries ONLY `ClosedLoopAuth` postconditions on
    /// the union of pre + post" reads
    /// `boundary.has_only_condition_kind(ConditionKind::ClosedLoopAuth)`
    /// at ONE call site rather than restating either widened
    /// composition. A `has-only-<kind>` require-tag classifier arm
    /// reaches this primitive at ONE substrate call — byte-for-byte
    /// peer of the tagged-union `has-only-<kind>` classifier one
    /// struct-layer up, closing the kind-scoped strict-refinement
    /// grid on the well-formed-diagonal arm at the Boundary struct
    /// layer alongside its sibling `has-<kind>` under the per-kind
    /// presence-probe axis.
    ///
    /// Theory anchor: THEORY.md §II.1 invariant 5 (composition
    /// preserves proofs — the kind-scoped strict-refinement projection
    /// composes the SAME fused short-circuit closed-set walk under
    /// [`Self::has_condition_kind`] on both this boundary surface and
    /// the ephemeral surface). THEORY.md §VI.1 (generation over
    /// composition — a new [`ConditionKind`] variant reaches both
    /// surfaces' kind-scoped strict-refinement triads mechanically
    /// through the delegated union primitive).
    #[must_use]
    pub fn has_only_condition_kind(&self, kind: ConditionKind) -> bool {
        let mut saw_kind = false;
        for k in ConditionKind::ALL {
            if !self.has_condition_kind(k) {
                continue;
            }
            if k == kind {
                saw_kind = true;
            } else {
                return false;
            }
        }
        saw_kind
    }

    /// `true` iff [`Self::preconditions`] carries at least one
    /// [`Condition`] with the given [`ConditionKind`] AND carries no
    /// [`Condition`] whose kind is anything OTHER than `kind` — the
    /// precondition-side arm of the (precondition, postcondition,
    /// condition-union) kind-scoped strict-refinement triad on
    /// [`Boundary`]. Thin typed delegate to
    /// [`ConditionSliceExt::has_only_kind`] over
    /// [`Self::preconditions`].
    ///
    /// Peer of [`Self::has_only_postcondition_kind`] on the
    /// (precondition, postcondition) partition of the boundary's two
    /// condition-vector slots; both peers compose against the SAME
    /// slice-level substrate primitive so a regression at the per-
    /// slice fused walk fails at that primitive's tests rather than
    /// as silent drift at either struct-level arm.
    #[must_use]
    pub fn has_only_precondition_kind(&self, kind: ConditionKind) -> bool {
        self.preconditions.has_only_kind(kind)
    }

    /// `true` iff [`Self::postconditions`] carries at least one
    /// [`Condition`] with the given [`ConditionKind`] AND carries no
    /// [`Condition`] whose kind is anything OTHER than `kind` — the
    /// postcondition-side arm of the (precondition, postcondition,
    /// condition-union) kind-scoped strict-refinement triad on
    /// [`Boundary`]. Thin typed delegate to
    /// [`ConditionSliceExt::has_only_kind`] over
    /// [`Self::postconditions`].
    ///
    /// Peer of [`Self::has_only_precondition_kind`]. See that method
    /// for the full rationale — the two methods share ONE lift
    /// motivation, ONE fail-before-pass-after composition-law pin,
    /// and ONE two-surface parity contract with the ephemeral sugar
    /// type via
    /// [`crate::ephemeral::EphemeralSpec::has_only_postcondition_kind`].
    #[must_use]
    pub fn has_only_postcondition_kind(&self, kind: ConditionKind) -> bool {
        self.postconditions.has_only_kind(kind)
    }

    /// `true` iff `preconditions ∪ postconditions` carries NO
    /// [`Condition`] with the given [`ConditionKind`] AND carries at
    /// least one [`Condition`] for every OTHER [`ConditionKind`] — the
    /// union arm of the (precondition, postcondition, condition-union)
    /// kind-scoped strict-refinement triad on [`Boundary`] specialized
    /// to the MISSING axis, byte-for-byte peer of the populated-axis
    /// [`Self::has_only_condition_kind`] under closed-set complement.
    ///
    /// # Composed body
    ///
    /// A FUSED short-circuit closed-set walk over
    /// [`ConditionKind::ALL`] under [`Self::has_condition_kind`] that
    /// skips every populated kind, returns `false` at the EARLIEST
    /// kind whose absence spans both slices' missing sets and is NOT
    /// `kind`, and returns `true` iff the sweep completes with `kind`
    /// seen as the sole missing kind. Strictly cheaper than the
    /// widened composition
    /// `boundary.missing_condition_kinds() == vec![kind]` (which
    /// allocates the missing-kind Vec before the equality test) or
    /// the (pre AND post) AND-of-strict-refinement
    /// `boundary.preconditions.lacks_only_kind(kind)
    ///     && boundary.postconditions.lacks_only_kind(kind)` (which is
    /// TOO STRICT — a single-slice-populated arrangement whose empty
    /// side returns `false` fails this AND but IS well-formed on the
    /// union).
    ///
    /// # Peer on the ephemeral surface — [`crate::ephemeral::EphemeralSpec::lacks_only_condition_kind`]
    ///
    /// Byte-identical signature `(&Self, ConditionKind) -> bool`,
    /// byte-identical fused-closed-set-walk body under complement, on
    /// the ephemeral sugar surface whose pre/post condition vectors
    /// live inline. Both methods compose against the SAME slice-level
    /// substrate primitive [`ConditionSliceExt::lacks_only_kind`] via
    /// the two-slice union composed through
    /// [`Self::has_condition_kind`] — a regression at the per-slice
    /// fused walk under complement fails at that primitive's tests
    /// rather than as silent drift at either struct-level kind-scoped-
    /// strict-refinement-on-missing caller.
    ///
    /// # Compounding
    ///
    /// A future coherence check verifying "every partially-attested
    /// closed-loop probe Process is missing ONLY the `ClosedLoopAuth`
    /// postcondition" reads
    /// `boundary.lacks_only_condition_kind(ConditionKind::ClosedLoopAuth)`
    /// at ONE call site rather than restating either widened
    /// composition. A `lacks-only-<kind>` require-tag classifier arm
    /// reaches this primitive at ONE substrate call — byte-for-byte
    /// peer of the tagged-union `lacks-only-<kind>` classifier one
    /// struct-layer up, CLOSING the kind-scoped strict-refinement 2x2
    /// grid on the Boundary struct layer alongside its populated-axis
    /// peer [`Self::has_only_condition_kind`].
    ///
    /// Theory anchor: THEORY.md §II.1 invariant 5 (composition
    /// preserves proofs — the kind-scoped strict-refinement projection
    /// on the missing axis composes the SAME fused short-circuit
    /// closed-set walk under [`Self::has_condition_kind`] on both this
    /// boundary surface and the ephemeral surface). THEORY.md §VI.1
    /// (generation over composition — a new [`ConditionKind`] variant
    /// reaches both surfaces' kind-scoped strict-refinement-on-missing
    /// triads mechanically through the delegated union primitive).
    #[must_use]
    pub fn lacks_only_condition_kind(&self, kind: ConditionKind) -> bool {
        let mut saw_kind = false;
        for k in ConditionKind::ALL {
            if self.has_condition_kind(k) {
                continue;
            }
            if k == kind {
                saw_kind = true;
            } else {
                return false;
            }
        }
        saw_kind
    }

    /// `true` iff [`Self::preconditions`] carries NO [`Condition`]
    /// with the given [`ConditionKind`] AND carries at least one
    /// [`Condition`] for every OTHER [`ConditionKind`] — the
    /// precondition-side arm of the (precondition, postcondition,
    /// condition-union) kind-scoped strict-refinement-on-missing triad
    /// on [`Boundary`]. Thin typed delegate to
    /// [`ConditionSliceExt::lacks_only_kind`] over
    /// [`Self::preconditions`].
    ///
    /// Peer of [`Self::lacks_only_postcondition_kind`] on the
    /// (precondition, postcondition) partition of the boundary's two
    /// condition-vector slots; both peers compose against the SAME
    /// slice-level substrate primitive so a regression at the per-
    /// slice fused walk under complement fails at that primitive's
    /// tests rather than as silent drift at either struct-level arm.
    #[must_use]
    pub fn lacks_only_precondition_kind(&self, kind: ConditionKind) -> bool {
        self.preconditions.lacks_only_kind(kind)
    }

    /// `true` iff [`Self::postconditions`] carries NO [`Condition`]
    /// with the given [`ConditionKind`] AND carries at least one
    /// [`Condition`] for every OTHER [`ConditionKind`] — the
    /// postcondition-side arm of the (precondition, postcondition,
    /// condition-union) kind-scoped strict-refinement-on-missing triad
    /// on [`Boundary`]. Thin typed delegate to
    /// [`ConditionSliceExt::lacks_only_kind`] over
    /// [`Self::postconditions`].
    ///
    /// Peer of [`Self::lacks_only_precondition_kind`]. See that method
    /// for the full rationale — the two methods share ONE lift
    /// motivation, ONE fail-before-pass-after composition-law pin,
    /// and ONE two-surface parity contract with the ephemeral sugar
    /// type via
    /// [`crate::ephemeral::EphemeralSpec::lacks_only_postcondition_kind`].
    #[must_use]
    pub fn lacks_only_postcondition_kind(&self, kind: ConditionKind) -> bool {
        self.postconditions.lacks_only_kind(kind)
    }

    /// `true` iff `preconditions ∪ postconditions` carries AT LEAST
    /// TWO [`Condition`] values with the given [`ConditionKind`] —
    /// the union arm of the (precondition, postcondition, condition-
    /// union) per-kind cardinality "≥ 2" many-arm triad on
    /// [`Boundary`]. Composes a two-step-short-circuit walk over the
    /// chained per-kind iterator [`Self::iter_condition_kind`], which
    /// itself chains [`ConditionSliceExt::iter_kind`] over
    /// [`Self::preconditions`] then [`Self::postconditions`].
    ///
    /// Composed body: pulls up to two hits off the chained per-kind
    /// iterator; returns `true` iff BOTH the first and the second are
    /// [`Some`]. Byte-for-byte peer of
    /// [`ConditionSliceExt::has_multiple_of_kind`] one slice-layer
    /// down, lifted to compose against the two-slice chain rather
    /// than a single slice's `iter_kind`. A regression at either
    /// per-slice many-arm walk fails at that primitive's substrate
    /// tests + the union composition-law tests rather than as silent
    /// drift here.
    ///
    /// # Peer on the ephemeral surface — [`crate::ephemeral::EphemeralSpec::has_multiple_of_condition_kind`]
    ///
    /// Byte-identical signature `(&Self, ConditionKind) -> bool`,
    /// byte-identical two-step short-circuit body composed against
    /// the ephemeral surface's own chained per-kind iterator. Both
    /// methods compose against the SAME slice-level substrate
    /// primitive [`ConditionSliceExt::has_multiple_of_kind`] via the
    /// two-slice chain — a regression at the per-slice many-arm walk
    /// fails at that primitive's tests rather than as silent drift
    /// at either struct-level `has-multiple-of-<kind>` caller.
    ///
    /// # Compounding
    ///
    /// A future operator-facing "duplicate boundary condition
    /// detected" audit reads
    /// `boundary.has_multiple_of_condition_kind(ConditionKind::ProcessPhase)`
    /// at ONE call site rather than restating
    /// `boundary.count_condition_kind(kind) >= 2` (which walks every
    /// slot on both slices to count) or the pre + post OR-composition
    /// with hand-authored short-circuit at every classifier arm.
    ///
    /// Theory anchor: THEORY.md §II.1 invariant 5 (composition
    /// preserves proofs — the per-kind cardinality-many-arm projection
    /// composes the SAME two-step short-circuit walk over the two-
    /// slice chain on both this boundary surface and the ephemeral
    /// surface). THEORY.md §VI.1 (generation over composition —
    /// a new [`ConditionKind`] variant reaches both surfaces'
    /// per-kind-many-arm triads mechanically through the delegated
    /// chained iterator).
    #[must_use]
    pub fn has_multiple_of_condition_kind(&self, kind: ConditionKind) -> bool {
        let mut it = self.iter_condition_kind(kind);
        it.next().is_some() && it.next().is_some()
    }

    /// `true` iff [`Self::preconditions`] carries AT LEAST TWO
    /// [`Condition`] values with the given [`ConditionKind`] — the
    /// precondition-side arm of the (precondition, postcondition,
    /// condition-union) per-kind cardinality "≥ 2" many-arm triad
    /// on [`Boundary`]. Thin typed delegate to
    /// [`ConditionSliceExt::has_multiple_of_kind`] over
    /// [`Self::preconditions`].
    ///
    /// Peer of [`Self::has_multiple_of_postcondition_kind`] on the
    /// (precondition, postcondition) partition of the boundary's two
    /// condition-vector slots; both peers compose against the SAME
    /// slice-level substrate primitive so a regression at the per-
    /// slice two-step short-circuit walk fails at that primitive's
    /// tests rather than as silent drift at either struct-level arm.
    #[must_use]
    pub fn has_multiple_of_precondition_kind(&self, kind: ConditionKind) -> bool {
        self.preconditions.has_multiple_of_kind(kind)
    }

    /// `true` iff [`Self::postconditions`] carries AT LEAST TWO
    /// [`Condition`] values with the given [`ConditionKind`] — the
    /// postcondition-side arm of the (precondition, postcondition,
    /// condition-union) per-kind cardinality "≥ 2" many-arm triad
    /// on [`Boundary`]. Thin typed delegate to
    /// [`ConditionSliceExt::has_multiple_of_kind`] over
    /// [`Self::postconditions`].
    ///
    /// Peer of [`Self::has_multiple_of_precondition_kind`]. See that
    /// method for the full rationale — the two methods share ONE
    /// lift motivation, ONE fail-before-pass-after composition-law
    /// pin, and ONE two-surface parity contract with the ephemeral
    /// sugar type via
    /// [`crate::ephemeral::EphemeralSpec::has_multiple_of_postcondition_kind`].
    #[must_use]
    pub fn has_multiple_of_postcondition_kind(&self, kind: ConditionKind) -> bool {
        self.postconditions.has_multiple_of_kind(kind)
    }

    /// `true` iff `preconditions ∪ postconditions` carries EXACTLY
    /// ONE [`Condition`] with the given [`ConditionKind`] — the union
    /// arm of the (precondition, postcondition, condition-union) per-
    /// kind cardinality "= 1" mid-endpoint triad on [`Boundary`].
    /// Composes a two-step-short-circuit walk over the chained per-
    /// kind iterator [`Self::iter_condition_kind`], which itself
    /// chains [`ConditionSliceExt::iter_kind`] over
    /// [`Self::preconditions`] then [`Self::postconditions`].
    ///
    /// Composed body: pulls up to two hits off the chained per-kind
    /// iterator; returns `true` iff the first is [`Some`] AND the
    /// second is [`None`]. Byte-for-byte peer of
    /// [`ConditionSliceExt::has_unique_of_kind`] one slice-layer
    /// down, lifted to compose against the two-slice chain rather
    /// than a single slice's `iter_kind`. Middle arm of the {= 0,
    /// = 1, ≥ 2} per-kind cardinality Boolean trichotomy at the
    /// union level: alongside [`Self::lacks_condition_kind`] (= 0)
    /// and [`Self::has_multiple_of_condition_kind`] (≥ 2), the three
    /// Booleans PARTITION the per-kind cardinality scalar's non-
    /// negative-integer arms — EXACTLY ONE fires on any `(boundary,
    /// kind)` pair.
    ///
    /// # Peer on the ephemeral surface — [`crate::ephemeral::EphemeralSpec::has_unique_of_condition_kind`]
    ///
    /// Byte-identical signature `(&Self, ConditionKind) -> bool`,
    /// byte-identical two-step short-circuit body composed against
    /// the ephemeral surface's own chained per-kind iterator. Both
    /// methods compose against the SAME slice-level substrate
    /// primitive [`ConditionSliceExt::has_unique_of_kind`] via the
    /// two-slice chain — a regression at the per-slice mid-endpoint
    /// walk fails at that primitive's tests rather than as silent
    /// drift at either struct-level `has-unique-of-<kind>` caller.
    ///
    /// # Compounding
    ///
    /// A future operator-facing "singleton boundary condition
    /// detected" audit reads
    /// `boundary.has_unique_of_condition_kind(ConditionKind::ProcessPhase)`
    /// at ONE call site rather than restating
    /// `boundary.count_condition_kind(kind) == 1` (which walks every
    /// slot on both slices to count) or the pre + post disjoint-arm
    /// OR-composition with hand-authored short-circuit at every
    /// classifier arm.
    ///
    /// Theory anchor: THEORY.md §II.1 invariant 5 (composition
    /// preserves proofs — the per-kind cardinality-mid-endpoint
    /// projection composes the SAME two-step short-circuit walk
    /// over the two-slice chain on both this boundary surface and
    /// the ephemeral surface). THEORY.md §VI.1 (generation over
    /// composition — a new [`ConditionKind`] variant reaches both
    /// surfaces' per-kind-mid-endpoint triads mechanically through
    /// the delegated chained iterator).
    #[must_use]
    pub fn has_unique_of_condition_kind(&self, kind: ConditionKind) -> bool {
        let mut it = self.iter_condition_kind(kind);
        it.next().is_some() && it.next().is_none()
    }

    /// `true` iff [`Self::preconditions`] carries EXACTLY ONE
    /// [`Condition`] with the given [`ConditionKind`] — the
    /// precondition-side arm of the (precondition, postcondition,
    /// condition-union) per-kind cardinality "= 1" mid-endpoint triad
    /// on [`Boundary`]. Thin typed delegate to
    /// [`ConditionSliceExt::has_unique_of_kind`] over
    /// [`Self::preconditions`].
    ///
    /// Peer of [`Self::has_unique_of_postcondition_kind`] on the
    /// (precondition, postcondition) partition of the boundary's two
    /// condition-vector slots; both peers compose against the SAME
    /// slice-level substrate primitive so a regression at the per-
    /// slice two-step short-circuit walk fails at that primitive's
    /// tests rather than as silent drift at either struct-level arm.
    #[must_use]
    pub fn has_unique_of_precondition_kind(&self, kind: ConditionKind) -> bool {
        self.preconditions.has_unique_of_kind(kind)
    }

    /// `true` iff [`Self::postconditions`] carries EXACTLY ONE
    /// [`Condition`] with the given [`ConditionKind`] — the
    /// postcondition-side arm of the (precondition, postcondition,
    /// condition-union) per-kind cardinality "= 1" mid-endpoint triad
    /// on [`Boundary`]. Thin typed delegate to
    /// [`ConditionSliceExt::has_unique_of_kind`] over
    /// [`Self::postconditions`].
    ///
    /// Peer of [`Self::has_unique_of_precondition_kind`]. See that
    /// method for the full rationale — the two methods share ONE
    /// lift motivation, ONE fail-before-pass-after composition-law
    /// pin, and ONE two-surface parity contract with the ephemeral
    /// sugar type via
    /// [`crate::ephemeral::EphemeralSpec::has_unique_of_postcondition_kind`].
    #[must_use]
    pub fn has_unique_of_postcondition_kind(&self, kind: ConditionKind) -> bool {
        self.postconditions.has_unique_of_kind(kind)
    }

    /// `true` iff `preconditions ∪ postconditions` carries AT MOST
    /// ONE [`Condition`] with the given [`ConditionKind`] — the
    /// union arm of the (precondition, postcondition, condition-
    /// union) per-kind cardinality "≤ 1" negation triad on
    /// [`Boundary`]. Closes the {= 0, = 1, ≥ 1, ≥ 2, ≤ 1} Boolean-
    /// cardinality grid on the per-kind axis at the union level
    /// alongside its sibling [`Self::has_multiple_of_condition_kind`]
    /// (≥ 2 many-arm) under the definitional negation
    /// `!(≥ 2) == (≤ 1)`. Composes a two-step-short-circuit walk over
    /// the chained per-kind iterator [`Self::iter_condition_kind`]
    /// via the definitional negation
    /// `!self.has_multiple_of_condition_kind(kind)`.
    ///
    /// Composed body: `!self.has_multiple_of_condition_kind(kind)` —
    /// a definitional Boolean negation of the union many-arm
    /// primitive. Short-circuits transitively through
    /// [`Self::has_multiple_of_condition_kind`]'s two-step short-
    /// circuit walk over the chained per-kind iterator: returns
    /// `true` as soon as the many-arm walk stops with fewer than
    /// two matches, WITHOUT walking every slot to build
    /// [`Self::count_condition_kind`]'s scalar. Byte-for-byte peer
    /// of [`ConditionSliceExt::has_at_most_one_of_kind`] one slice-
    /// layer down, lifted to compose against the two-slice chain
    /// rather than a single slice's `iter_kind`.
    ///
    /// # Peer on the ephemeral surface — [`crate::ephemeral::EphemeralSpec::has_at_most_one_of_condition_kind`]
    ///
    /// Byte-identical signature `(&Self, ConditionKind) -> bool`,
    /// byte-identical definitional-negation body composed against
    /// the ephemeral surface's own chained per-kind iterator. Both
    /// methods compose against the SAME slice-level substrate
    /// primitive [`ConditionSliceExt::has_at_most_one_of_kind`] via
    /// the two-slice chain — a regression at the per-slice negation
    /// walk fails at that primitive's tests rather than as silent
    /// drift at either struct-level `has-at-most-one-of-<kind>`
    /// caller.
    ///
    /// # Compounding
    ///
    /// A future authoring-time linter that surfaces "boundary
    /// condition slice union has no duplicates for kind K" reads
    /// `boundary.has_at_most_one_of_condition_kind(K)` at ONE call
    /// site rather than restating
    /// `!boundary.has_multiple_of_condition_kind(K)` or
    /// `boundary.count_condition_kind(K) <= 1` (which walks every
    /// slot on both slices to count) at every callsite. A future
    /// operator-facing "no-duplicate-of-kind" postcondition-well-
    /// formedness check that allows either absence (0 matches) or a
    /// single reference (1 match) but rejects duplicates reads this
    /// primitive with a single call.
    ///
    /// Theory anchor: THEORY.md §II.1 invariant 5 (composition
    /// preserves proofs — the per-kind cardinality-"≤ 1" projection
    /// composes the SAME definitional negation shape over the two-
    /// slice chain on both this boundary surface and the ephemeral
    /// surface). THEORY.md §VI.1 (generation over composition — a
    /// new [`ConditionKind`] variant reaches both surfaces' per-
    /// kind-"≤ 1" triads mechanically through the delegated chained
    /// iterator).
    #[must_use]
    pub fn has_at_most_one_of_condition_kind(&self, kind: ConditionKind) -> bool {
        !self.has_multiple_of_condition_kind(kind)
    }

    /// `true` iff [`Self::preconditions`] carries AT MOST ONE
    /// [`Condition`] with the given [`ConditionKind`] — the
    /// precondition-side arm of the (precondition, postcondition,
    /// condition-union) per-kind cardinality "≤ 1" negation triad
    /// on [`Boundary`]. Thin typed delegate to
    /// [`ConditionSliceExt::has_at_most_one_of_kind`] over
    /// [`Self::preconditions`].
    ///
    /// Peer of [`Self::has_at_most_one_of_postcondition_kind`] on
    /// the (precondition, postcondition) partition of the
    /// boundary's two condition-vector slots; both peers compose
    /// against the SAME slice-level substrate primitive so a
    /// regression at the per-slice definitional negation walk fails
    /// at that primitive's tests rather than as silent drift at
    /// either struct-level arm.
    #[must_use]
    pub fn has_at_most_one_of_precondition_kind(&self, kind: ConditionKind) -> bool {
        self.preconditions.has_at_most_one_of_kind(kind)
    }

    /// `true` iff [`Self::postconditions`] carries AT MOST ONE
    /// [`Condition`] with the given [`ConditionKind`] — the
    /// postcondition-side arm of the (precondition, postcondition,
    /// condition-union) per-kind cardinality "≤ 1" negation triad
    /// on [`Boundary`]. Thin typed delegate to
    /// [`ConditionSliceExt::has_at_most_one_of_kind`] over
    /// [`Self::postconditions`].
    ///
    /// Peer of [`Self::has_at_most_one_of_precondition_kind`]. See
    /// that method for the full rationale — the two methods share
    /// ONE lift motivation, ONE fail-before-pass-after composition-
    /// law pin, and ONE two-surface parity contract with the
    /// ephemeral sugar type via
    /// [`crate::ephemeral::EphemeralSpec::has_at_most_one_of_postcondition_kind`].
    #[must_use]
    pub fn has_at_most_one_of_postcondition_kind(&self, kind: ConditionKind) -> bool {
        self.postconditions.has_at_most_one_of_kind(kind)
    }

    /// Returns the unique [`Condition`] with the given
    /// [`ConditionKind`] in `preconditions ∪ postconditions`, or
    /// [`None`] if zero or `≥ 2` such [`Condition`]s exist — the
    /// union arm of the (precondition, postcondition, condition-
    /// union) `Option<&Condition>`-witnessing peer of the Boolean
    /// [`Self::has_unique_of_condition_kind`] on the per-kind
    /// cardinality "= 1" mid-endpoint at the boundary level.
    /// Composed body: a two-step short-circuit walk over the chained
    /// per-kind iterator [`Self::iter_condition_kind`] — pulls at
    /// most two matches from the pre-then-post chain, returns the
    /// first iff no second exists. Byte-for-byte peer of
    /// [`ConditionSliceExt::unique_of_kind`] one slice-layer down,
    /// lifted to compose against the two-slice chain rather than a
    /// single slice's `iter_kind`.
    ///
    /// Composition laws:
    /// - `has_unique_of_condition_kind(k) == unique_of_condition_kind(k).is_some()`
    /// - `unique_of_condition_kind(k).map(|c| c.kind) == Some(k)` iff
    ///   `has_unique_of_condition_kind(k)`, else `None`.
    ///
    /// # Peer on the ephemeral surface — [`crate::ephemeral::EphemeralSpec::unique_of_condition_kind`]
    ///
    /// Byte-identical signature `(&Self, ConditionKind) ->
    /// Option<&Condition>`, byte-identical two-step short-circuit
    /// body composed against the ephemeral surface's own chained
    /// per-kind iterator. Both methods compose against the SAME
    /// slice-level substrate primitive
    /// [`ConditionSliceExt::unique_of_kind`] via the two-slice
    /// chain — a regression at the per-slice witness walk fails at
    /// that primitive's tests rather than as silent drift at either
    /// struct-level `unique-of-<kind>` caller.
    ///
    /// # Compounding
    ///
    /// A future coherence check that inspects "the unique
    /// [`ConditionKind::ClosedLoopAuth`] postcondition's `issuer`
    /// param" reads
    /// `boundary.unique_of_condition_kind(ConditionKind::ClosedLoopAuth)`
    /// at ONE call site rather than restating
    /// `if boundary.has_unique_of_condition_kind(k) { boundary.find_condition_kind(k) } else { None }`
    /// (which walks the chain twice) or the pre + post disjoint-arm
    /// composition at every classifier arm.
    ///
    /// Theory anchor: THEORY.md §II.1 invariant 5 (composition
    /// preserves proofs — the per-kind `Option<&Condition>`
    /// witnessing refinement composes the SAME two-step short-
    /// circuit walk over the two-slice chain on both this boundary
    /// surface and the ephemeral surface). THEORY.md §VI.1
    /// (generation over composition — a new [`ConditionKind`]
    /// variant reaches both surfaces' per-kind-witness triads
    /// mechanically through the delegated chained iterator).
    #[must_use]
    pub fn unique_of_condition_kind(&self, kind: ConditionKind) -> Option<&Condition> {
        let mut it = self.iter_condition_kind(kind);
        let first = it.next()?;
        match it.next() {
            None => Some(first),
            Some(_) => None,
        }
    }

    /// Returns the unique [`Condition`] with the given
    /// [`ConditionKind`] in [`Self::preconditions`], or [`None`] if
    /// zero or `≥ 2` such [`Condition`]s exist — the precondition-
    /// side arm of the (precondition, postcondition, condition-
    /// union) `Option<&Condition>`-witnessing peer triad on
    /// [`Boundary`]. Thin typed delegate to
    /// [`ConditionSliceExt::unique_of_kind`] over
    /// [`Self::preconditions`].
    ///
    /// Peer of [`Self::unique_of_postcondition_kind`] on the
    /// (precondition, postcondition) partition of the boundary's two
    /// condition-vector slots; both peers compose against the SAME
    /// slice-level substrate primitive so a regression at the per-
    /// slice two-step short-circuit walk fails at that primitive's
    /// tests rather than as silent drift at either struct-level arm.
    #[must_use]
    pub fn unique_of_precondition_kind(&self, kind: ConditionKind) -> Option<&Condition> {
        self.preconditions.unique_of_kind(kind)
    }

    /// Returns the unique [`Condition`] with the given
    /// [`ConditionKind`] in [`Self::postconditions`], or [`None`] if
    /// zero or `≥ 2` such [`Condition`]s exist — the postcondition-
    /// side arm of the (precondition, postcondition, condition-
    /// union) `Option<&Condition>`-witnessing peer triad on
    /// [`Boundary`]. Thin typed delegate to
    /// [`ConditionSliceExt::unique_of_kind`] over
    /// [`Self::postconditions`].
    ///
    /// Peer of [`Self::unique_of_precondition_kind`]. See that method
    /// for the full rationale — the two methods share ONE lift
    /// motivation, ONE fail-before-pass-after composition-law pin,
    /// and ONE two-surface parity contract with the ephemeral sugar
    /// type via
    /// [`crate::ephemeral::EphemeralSpec::unique_of_postcondition_kind`].
    #[must_use]
    pub fn unique_of_postcondition_kind(&self, kind: ConditionKind) -> Option<&Condition> {
        self.postconditions.unique_of_kind(kind)
    }
}

/// Slice-level `(ConditionKind, presence)` probe on any `&[Condition]`
/// — the ONE substrate primitive that owns the
/// `.iter().any(|c| c.kind == K)` walk shape both current production
/// sites hand-authored past the ★★ PRIME-DIRECTIVE ≥ 2 duplication
/// threshold. Callers compose the two-half union at their site
/// ([`Boundary::has_condition_kind`] on `preconditions ∪
/// postconditions`) or on ONE half only (the ephemeral require-tag
/// classifier's `closed-loop-auth` arm on `spec.postconditions`) —
/// the primitive owns ONLY the per-slice walk, so the composition
/// choice stays typed at the caller.
///
/// # Why lift
///
/// Pre-lift the `.iter().any(|c| c.kind == K)` walk lived
/// hand-authored at THREE production sites: twice inside
/// [`Boundary::has_condition_kind`]'s union (pre + post), once at
/// `evaluate_ephemeral_require_tag`'s `closed-loop-auth` arm in
/// `tatara-reconciler::bin::tatara-check` (with `matches!` sugar
/// instead of `==`, but the same predicate). The (`&[Condition]`,
/// `ConditionKind`) → `bool` shape is the substrate primitive: a
/// future consumer that walks a `Vec<Condition>` (a coherence check
/// that verifies "every `ClosedLoopAuth` postcondition carries an
/// `issuer` param key", an editor completion listing which
/// [`ConditionKind`] arms appear on ONE side only, a hypothetical
/// `postcondition-<kind>` require-tag prefix family that dispatches
/// on `postconditions` alone — the peer of the existing
/// `condition-<kind>` family that dispatches on the pre ∪ post union
/// via [`Boundary::has_condition_kind`]) reaches this ONE primitive
/// through `slice.has_kind(k)` instead of restating the `.iter().any`
/// closure body.
///
/// # Sibling to [`Boundary::has_condition_kind`]
///
/// Same axis, one refinement lower: `Boundary::has_condition_kind` is
/// the two-slice-union probe; `has_kind` here is the one-slice probe
/// the union composes twice. A future normalization at the presence
/// probe shape (widening the return to `Option<&Condition>` for
/// deeper diagnostics, adding a debug-build assertion on redundant
/// duplicates, switching to a linear scan that also counts matches)
/// lands at ONE site here — both [`Boundary::has_condition_kind`] +
/// every downstream `slice.has_kind(K)` callsite pick it up
/// mechanically.
///
/// # Compounding
///
/// [`Self::find_kind`] is the widened primitive returning
/// `Option<&Condition>` that both `has_kind` (`self.find_kind(k).
/// is_some()`, the default body) and future diagnostic consumers
/// compose against. A `has_kind_matching(|&Condition| -> bool)`
/// predicate extension similarly lands as ONE new default method on
/// this trait — the closed-set discriminator case becomes `has_kind(k)
/// == self.has_kind_matching(|c| c.kind == k)` by construction, so a
/// regression that drifted one from the other becomes structurally
/// impossible past the trait boundary.
///
/// Theory anchor: THEORY.md §II.1 invariant 5 — composition preserves
/// proofs; the per-slice walk lives at ONE substrate site so the
/// two-half union in [`Boundary`] and the one-half probe on
/// [`crate::ephemeral::EphemeralSpec::postconditions`] compose
/// through the SAME primitive. THEORY.md §VI.1 — generation over
/// composition; a future `Vec<Condition>` consumer reaches the
/// primitive through `slice.has_kind(k)` with no per-caller
/// restatement of the `.iter().any(|c| c.kind == K)` closure body.
pub trait ConditionSliceExt {
    /// Returns an iterator yielding every [`Condition`] in this slice
    /// whose [`Condition::kind`] equals `kind`, in slice order — the
    /// ONE widened primitive on the slice-level presence-probe axis
    /// that both [`Self::find_kind`] (via the default
    /// `iter_kind(k).next()` body) and [`Self::has_kind`] (via the
    /// transitive `find_kind(k).is_some()` default) compose against.
    ///
    /// # Sibling to [`Self::find_kind`]
    ///
    /// One refinement wider: `find_kind` collapses the return to
    /// `Option<&Condition>` (yielding only the earliest match);
    /// `iter_kind` returns the whole match stream so callers can
    /// [`count`](Iterator::count) it, [`collect`](Iterator::collect)
    /// it into a `Vec<&Condition>`, ask for the
    /// [`nth`](Iterator::nth) element, or compose it with any other
    /// std iterator adaptor without re-walking the slice. The default
    /// body of `find_kind` is `self.iter_kind(kind).next()` — the
    /// two methods share ONE walk semantics by construction, so a
    /// regression that drifted the first-match probe from the
    /// widened stream becomes structurally impossible past the
    /// trait boundary.
    ///
    /// # Semantics
    ///
    /// Yields `&c` for each `c` in this slice with `c.kind == kind`,
    /// in slice order — a slice that carries multiple matches yields
    /// each in turn (the composition law
    /// `find_kind(k) == iter_kind(k).next()` binds the first match
    /// to the earliest position). An empty slice, or a slice with no
    /// matching kind, yields nothing. Byte-for-byte equivalent to
    /// `self.iter().filter(|c| c.kind == kind)`.
    ///
    /// # Compounding
    ///
    /// A future coherence check that verifies "each
    /// [`ConditionKind`] appears at most once per side" reads
    /// `slice.iter_kind(k).nth(1).is_none()` at ONE call site
    /// rather than restating the count-with-filter closure body.
    /// A future diagnostic that enumerates every match of a kind
    /// (an operator-facing "3 PromQL preconditions matched" message,
    /// an audit dump listing every match of a repeated kind) reaches
    /// this ONE primitive through `slice.iter_kind(k).collect()`
    /// rather than re-walking the slice with `.iter().filter(...)`
    /// at the callsite. The presence-probe axis now carries three
    /// refinements (bool via `has_kind`, `Option<&Condition>` via
    /// `find_kind`, `impl Iterator<Item = &Condition>` via
    /// `iter_kind`) at ONE typed algebra surface — every downstream
    /// consumer picks the coarsest one that answers its question and
    /// the coarser ones stay compositionally derived from this
    /// primitive.
    fn iter_kind(&self, kind: ConditionKind) -> KindMatches<'_>;

    /// Returns the first [`Condition`] in this slice that carries the
    /// given [`ConditionKind`], or `None` if none matches. Default
    /// body: `self.iter_kind(kind).next()` — a thin projection of the
    /// widened primitive [`Self::iter_kind`] onto its first element.
    /// The composition law `find_kind(k) == iter_kind(k).next()`
    /// binds the first-match probe to the widened stream at the
    /// trait's default body.
    ///
    /// # Sibling to [`Self::has_kind`]
    ///
    /// One refinement wider: `has_kind` collapses the return to a
    /// `bool`; `find_kind` returns the matching `&Condition` so
    /// callers can read [`Condition::params`] without re-walking the
    /// slice. The default body of `has_kind` is
    /// `self.find_kind(kind).is_some()` — the two methods share ONE
    /// walk semantics by construction. Byte-for-byte equivalent to
    /// `self.iter().find(|c| c.kind == kind)`.
    fn find_kind(&self, kind: ConditionKind) -> Option<&Condition> {
        self.iter_kind(kind).next()
    }

    /// True iff at least one [`Condition`] in this slice carries the
    /// given [`ConditionKind`]. Default body: `self.find_kind(kind).
    /// is_some()`. The single-slice presence probe both
    /// [`Boundary::has_condition_kind`] (twice, in a union) and the
    /// ephemeral `closed-loop-auth` require-tag arm (once, on
    /// postconditions only) compose against.
    fn has_kind(&self, kind: ConditionKind) -> bool {
        self.find_kind(kind).is_some()
    }

    /// Number of [`Condition`]s in this slice carrying the given
    /// [`ConditionKind`] — the scalar cardinality refinement on the
    /// slice-level presence-probe axis. Default body:
    /// `self.iter_kind(kind).count()` — a thin projection of the
    /// widened primitive [`Self::iter_kind`] onto its cardinality.
    ///
    /// # Sibling to [`Self::iter_kind`] / [`Self::find_kind`] / [`Self::has_kind`]
    ///
    /// Fourth refinement on the presence-probe algebra: `iter_kind`
    /// yields the whole match stream, `find_kind` collapses it to the
    /// first match, `has_kind` collapses that to a `bool`, and
    /// `count_kind` collapses the stream to its cardinality without
    /// materializing any intermediate [`Vec`] or `Option`. The
    /// composition laws
    /// `count_kind(k) == iter_kind(k).count()`,
    /// `has_kind(k) == (count_kind(k) > 0)`, and
    /// `find_kind(k).is_some() == (count_kind(k) > 0)`
    /// share ONE walk semantics by construction; a regression that
    /// drifted the cardinality probe from the widened stream becomes
    /// structurally impossible past the trait boundary.
    ///
    /// # Semantics
    ///
    /// Returns `self.iter().filter(|c| c.kind == kind).count()` — a
    /// slice that carries multiple matches returns that count, an
    /// empty slice or a slice with no matching kind returns `0`.
    ///
    /// # Compounding
    ///
    /// A future coherence check that verifies "each [`ConditionKind`]
    /// appears at most once per side" now reads
    /// `slice.count_kind(k) <= 1` at ONE call site rather than
    /// restating either `slice.iter_kind(k).nth(1).is_none()` or the
    /// `iter_kind(k).count() <= 1` idiom. A future require-tag
    /// classifier arm that surfaces multiplicity to the operator
    /// (a hypothetical `condition-count-<kind>` prefix family that
    /// publishes the raw cardinality, an audit dump reporting "3
    /// PromQL preconditions matched") reaches this ONE primitive
    /// through `slice.count_kind(k)` rather than restating the
    /// `.iter_kind(k).count()` chain body at the callsite. The
    /// presence-probe axis now carries FOUR refinements at ONE typed
    /// algebra surface — every downstream consumer picks the coarsest
    /// one that answers its question and the coarser ones stay
    /// compositionally derived from [`Self::iter_kind`].
    fn count_kind(&self, kind: ConditionKind) -> usize {
        self.iter_kind(kind).count()
    }

    /// The set of [`ConditionKind`] variants that appear at least once in
    /// this slice, projected in [`ConditionKind::ALL`] order — the
    /// closed-set-inversion refinement on the slice-level presence-probe
    /// axis. Default body: `ConditionKind::ALL.into_iter().filter(|k|
    /// self.has_kind(*k)).collect()` — a thin projection over the closed
    /// set that composes against [`Self::has_kind`] per variant.
    ///
    /// # Sibling to [`Self::has_kind`] / [`Self::find_kind`] / [`Self::iter_kind`] / [`Self::count_kind`]
    ///
    /// FIFTH refinement on the presence-probe algebra, distinct in axis
    /// from the other four: `has_kind` / `find_kind` / `iter_kind` /
    /// `count_kind` fix a [`ConditionKind`] and vary the return type
    /// (bool / `Option<&Condition>` / `impl Iterator<Item = &Condition>` /
    /// `usize`); this refinement INVERTS the axis by fixing the slice and
    /// varying over [`ConditionKind::ALL`], returning the SET of present
    /// kinds. The composition law
    /// `distinct_kinds().contains(&k) == has_kind(k)` for every
    /// `k ∈ ConditionKind::ALL` binds the closed-set-inversion probe to
    /// the point probe at the trait's default body.
    ///
    /// # Semantics — canonical subsequence of [`ConditionKind::ALL`]
    ///
    /// Returns a `Vec<ConditionKind>` whose elements appear in
    /// [`ConditionKind::ALL`] order with no duplicates. A slice that
    /// carries the same [`ConditionKind`] at multiple positions
    /// contributes ONE entry to the returned set (the closed-set
    /// projection collapses multiplicity — a caller that needs the
    /// per-kind cardinality reaches for [`Self::count_kind`]). An
    /// empty slice, or a slice with no matching kind under any
    /// [`ConditionKind::ALL`] variant, returns an empty vec.
    ///
    /// # Why closed-set-inversion is a distinct axis
    ///
    /// The other four refinements answer "for THIS kind, how does the
    /// slice populate the probe's return type?"; this refinement
    /// answers "for THIS slice, which kinds appear at least once?".
    /// A consumer that needs to enumerate every present kind for an
    /// audit dump (`"boundary carries [PromQL, ClosedLoopAuth]"`), a
    /// coherence check that verifies "every process's boundary carries
    /// at least ONE of {`JobAttested`, `ClosedLoopAuth`}", or a
    /// require-tag family that surfaces the distinct-set as a whole
    /// (`condition-kinds-distinct-count`) reaches this refinement
    /// rather than paying for a per-kind sweep with `has_kind` at the
    /// callsite. The point probe stays composable one axis over
    /// (`slice.has_kind(k)` for a fixed `k`); the aggregate refinement
    /// lives at the same trait, one axis away.
    ///
    /// # Compounding
    ///
    /// A future coherence check that enforces "every boundary carries
    /// at least ONE distinct kind" (a warning surfaced when
    /// `boundary.distinct_condition_kinds().is_empty()`) reaches this
    /// ONE primitive rather than paying for the eight-way
    /// `for k in ConditionKind::ALL { if boundary.has_condition_kind(k)
    /// { return true; } }` sweep at every callsite. A future require-
    /// tag classifier arm that publishes the distinct-set cardinality
    /// as a scalar (a hypothetical `condition-kinds-distinct-<n>`
    /// prefix family, an audit dump reporting "boundary carries N
    /// distinct kinds") reaches this ONE primitive through
    /// `boundary.distinct_condition_kinds().len()` rather than
    /// restating the closed-set-inverted `.iter().filter(...).count()`
    /// idiom at every callsite. The presence-probe axis now carries
    /// FIVE refinements at ONE typed algebra surface — the four point-
    /// probes fixing a kind AND the ONE closed-set-inversion probe
    /// fixing a slice — every downstream consumer picks the one that
    /// answers its question and the others stay compositionally
    /// derived from the single-source-of-truth widened primitive.
    ///
    /// # Theory grounding
    ///
    /// - THEORY.md §II.1 invariant 5 — composition preserves proofs.
    ///   The closed-set-inversion projection lives at ONE substrate
    ///   site as a typed projection of [`Self::has_kind`] over the
    ///   closed set [`ConditionKind::ALL`]. Every downstream aggregate
    ///   consumer binds through the SAME shape rather than restating
    ///   the ALL-filter closure body.
    /// - THEORY.md §VI.1 — generation over composition. A new
    ///   [`ConditionKind`] variant added to `ALL` reaches this
    ///   primitive mechanically (the closed-set walk picks up the new
    ///   entry) and every downstream consumer sees the wider set
    ///   without further per-caller edit.
    fn distinct_kinds(&self) -> Vec<ConditionKind> {
        self.iter_distinct_kinds().collect()
    }

    /// Zero-allocation iterator peer of [`Self::distinct_kinds`] — walk
    /// [`ConditionKind::ALL`] in canonical order and yield every
    /// [`ConditionKind`] whose corresponding slot on this slice is
    /// populated (at least one [`Condition`] with that kind), WITHOUT
    /// materializing an intermediate [`Vec<ConditionKind>`].
    ///
    /// Default body:
    /// `ConditionKind::ALL.iter().copied().filter(|&k| self.has_kind(k))`.
    /// The composition law
    /// `distinct_kinds() == iter_distinct_kinds().collect::<Vec<_>>()`
    /// holds by construction — [`Self::distinct_kinds`]'s default body IS
    /// `self.iter_distinct_kinds().collect()`, so a caller that overrides
    /// the widened Vec primitive with a divergent walk simultaneously
    /// drifts both surfaces (surfacing at the substrate testkit
    /// [`assert_slice_refinement_composition_laws`] which pins the Vec
    /// projection equals `iter().collect()`).
    ///
    /// # Sibling to [`Self::distinct_kinds`] / [`Self::distinct_kind_count`]
    ///
    /// Load-bearing iterator peer of the slice-level closed-set-inversion
    /// axis — where `distinct_kinds` returns the SET (heap-allocated
    /// `Vec`, canonical `ConditionKind::ALL` order) and
    /// `distinct_kind_count` scalar-projects its cardinality,
    /// `iter_distinct_kinds` opens the walk as a `Copy` iterator so
    /// consumers that need a short-circuiting fold (`.any(|k| pred(k))`,
    /// `.find(|&k| pred(k))`, `.take_while(|k| pred(k))`, `.map(|k|
    /// project(k))`) avoid the intermediate allocation entirely.
    ///
    /// # Peer to [`crate::tagged_union::TaggedUnion::iter_populated_kinds`]
    ///
    /// Same shape at the peer axis one struct layer up: where
    /// `iter_populated_kinds` opens the closed-set-inversion walk on the
    /// tagged-union parent-level presence-probe axis,
    /// `iter_distinct_kinds` opens the closed-set-inversion walk on the
    /// slice-level presence-probe axis. Both close the "load-bearing
    /// iterator" refinement at two adjacent typescape sites through the
    /// SAME `<CLOSED_SET>::ALL.iter().copied().filter(|&k| has_probe(k))`
    /// composition body under a POSITIVE point-probe.
    ///
    /// # Compounding future consumers
    ///
    /// - Every scalar closed-set-inversion peer already at the trait
    ///   (`distinct_kind_count`, `first_distinct_kind`,
    ///   `last_distinct_kind`, `unique_distinct_kind`,
    ///   `has_any_distinct_kind`) folds a specialization of
    ///   `ConditionKind::ALL.iter().filter(|k| self.has_kind(**k))` —
    ///   they can compose over `iter_distinct_kinds()` at ONE substrate
    ///   site rather than restating the closed-set walk body per peer.
    /// - A downstream diagnostic composer (an operator-facing "boundary
    ///   carries: [{}]" message that streams the label list into a
    ///   `write!` buffer) reads `slice.iter_distinct_kinds().map(|k|
    ///   k.label())` and folds through `itertools::join` without the
    ///   allocation `Vec<ConditionKind> -> String` pays.
    ///
    /// # Theory grounding
    ///
    /// - THEORY.md §II.1 invariant 5 — composition preserves proofs.
    ///   The load-bearing iterator projection lives at ONE substrate
    ///   site; every downstream aggregate consumer refines it through a
    ///   standard-library iterator fold rather than restating the
    ///   [`ConditionKind::ALL`]-walk closure body.
    /// - THEORY.md §VI.1 — generation over composition. A new
    ///   [`ConditionKind`] variant added to `ALL` reaches the walk
    ///   mechanically (the closed-set filter picks up the new entry) and
    ///   every downstream fold sees the wider set without further
    ///   per-caller edit.
    fn iter_distinct_kinds(&self) -> impl Iterator<Item = ConditionKind> + '_ {
        ConditionKind::ALL
            .iter()
            .copied()
            .filter(|&k| self.has_kind(k))
    }

    /// Scalar cardinality projection of [`Self::distinct_kinds`] onto
    /// its `.len()` — the number of [`ConditionKind`] variants that
    /// appear at least once in this slice. Default body:
    /// `ConditionKind::ALL.iter().filter(|k| self.has_kind(**k)).count()`
    /// — a closed-set walk that composes against [`Self::has_kind`] per
    /// variant WITHOUT materializing an intermediate `Vec<ConditionKind>`.
    /// A slice that carries the same [`ConditionKind`] at multiple
    /// positions contributes `1` to the count (the closed-set projection
    /// collapses multiplicity — a caller that needs the per-kind
    /// cardinality reaches for [`Self::count_kind`]).
    ///
    /// # Sibling to [`Self::distinct_kinds`]
    ///
    /// Scalar projection of the closed-set-inversion widened primitive
    /// — where `distinct_kinds` returns the SET (a `Vec<ConditionKind>`
    /// in canonical [`ConditionKind::ALL`] order), `distinct_kind_count`
    /// collapses that set to its cardinality. The composition law
    /// `distinct_kind_count() == distinct_kinds().len()` binds the
    /// scalar projection to the widened primitive at the trait's
    /// default body and is swept substrate-wide by
    /// [`assert_slice_refinement_composition_laws`] as its sixth arm.
    ///
    /// # Peer to [`crate::tagged_union::TaggedUnion::populated_kind_count`]
    ///
    /// Same shape at the peer axis one struct layer up: where
    /// `populated_kind_count` scalar-projects `populated_kinds` on the
    /// tagged-union parent-level closed-set-inversion axis,
    /// `distinct_kind_count` scalar-projects `distinct_kinds` on the
    /// slice-level closed-set-inversion axis. The two primitives close
    /// the scalar-cardinality refinement at two adjacent typescape
    /// sites — one per closed-set-addressed slice-level refinement,
    /// one per closed-set-addressed tagged-union parent-level
    /// refinement — through the SAME `ClosedSet::ALL`-walk shape.
    ///
    /// # Compounding future consumers
    ///
    /// - A future coherence check that enforces "every boundary carries
    ///   at least ONE distinct kind" now reads
    ///   `slice.distinct_kind_count() > 0` at ONE call site rather than
    ///   paying for `slice.distinct_kinds().len() > 0` (with its
    ///   intermediate heap allocation) or the eight-way sweep with
    ///   `has_kind` at the callsite.
    /// - A future require-tag classifier arm that surfaces the
    ///   distinct-set cardinality as a scalar (a hypothetical
    ///   `condition-kinds-distinct-<n>` prefix family named in
    ///   [`Self::distinct_kinds`]'s doc-comment as a compounding-future
    ///   consumer) reaches this ONE primitive without allocating.
    /// - A future audit dump reporting "boundary carries N distinct
    ///   kinds" reaches `slice.distinct_kind_count()` directly rather
    ///   than restating the `.iter().filter(...).count()` closure body.
    ///
    /// # Theory grounding
    ///
    /// - THEORY.md §II.1 invariant 5 — composition preserves proofs.
    ///   The scalar cardinality lives at ONE substrate site as a typed
    ///   projection of [`Self::distinct_kinds`] onto its `.len()`, and
    ///   the default body composes against [`Self::has_kind`] over the
    ///   closed set [`ConditionKind::ALL`] byte-identically to
    ///   `distinct_kinds` without the intermediate `Vec`. Every
    ///   downstream aggregate consumer binds through the SAME shape
    ///   rather than paying for the allocation to reach the
    ///   cardinality.
    /// - THEORY.md §VI.1 — generation over composition. A new
    ///   [`ConditionKind`] variant added to `ALL` reaches this
    ///   primitive mechanically (the closed-set walk picks up the new
    ///   entry) and every downstream consumer sees the wider
    ///   cardinality without further per-caller edit.
    fn distinct_kind_count(&self) -> usize {
        self.iter_distinct_kinds().count()
    }

    /// The set of [`ConditionKind`] variants that do NOT appear in this
    /// slice, projected in [`ConditionKind::ALL`] order — the closed-
    /// set-inversion COMPLEMENT of [`Self::distinct_kinds`]. Default
    /// body: `ConditionKind::ALL.into_iter().filter(|k|
    /// !self.has_kind(*k)).collect()` — a thin projection over the
    /// closed set that composes against [`Self::has_kind`] per variant
    /// under a negated predicate.
    ///
    /// # Sibling to [`Self::distinct_kinds`]
    ///
    /// Complement peer of the closed-set-inversion widened primitive on
    /// the slice-level presence-probe axis. Where `distinct_kinds`
    /// returns the SET of kinds that DO appear at least once,
    /// `missing_kinds` returns the SET of kinds that DO NOT appear.
    /// Both walk [`ConditionKind::ALL`] in canonical order and compose
    /// against the same [`Self::has_kind`] point probe. The two
    /// widened primitives PARTITION [`ConditionKind::ALL`]: their union
    /// equals `ConditionKind::ALL`, their intersection is empty, and
    /// their cardinalities sum to `ConditionKind::ALL.len()` — three
    /// composition laws pinned as the seventh, eighth, and ninth arms
    /// of the substrate testkit
    /// [`assert_slice_refinement_composition_laws`].
    ///
    /// # Peer to [`crate::tagged_union::TaggedUnion::populated_kinds`]'s
    /// hypothetical `unpopulated_kinds` complement
    ///
    /// Same shape at the peer axis one struct layer up: fixing the
    /// parent-side carrier and inverting the presence probe over the
    /// closed set. The two primitives close the "closed-set complement"
    /// refinement at two adjacent typescape sites — one per closed-set-
    /// addressed slice-level refinement (this primitive), one per
    /// closed-set-addressed tagged-union parent-level refinement (a
    /// symmetric future addition).
    ///
    /// # Semantics — canonical subsequence of [`ConditionKind::ALL`]
    ///
    /// Returns a `Vec<ConditionKind>` whose elements appear in
    /// [`ConditionKind::ALL`] order with no duplicates. An empty slice
    /// returns `ConditionKind::ALL.to_vec()` (every kind is missing).
    /// A slice that carries every variant returns an empty vec (no kind
    /// is missing). A slice that carries the same [`ConditionKind`] at
    /// multiple positions still contributes ZERO entries to the missing
    /// set at that kind (the closed-set complement is a SET operation —
    /// multiplicity on the present side is irrelevant to absence on the
    /// missing side).
    ///
    /// # Compounding future consumers
    ///
    /// - A future coherence check that enforces "every process boundary
    ///   carries a [`ConditionKind::JobAttested`] postcondition" now
    ///   surfaces the operator-facing diagnostic
    ///   `spec.boundary.postconditions.missing_kinds()` verbatim
    ///   (naming EVERY kind absent from postconditions in canonical
    ///   order) rather than reaching for `!has_kind(JobAttested)` at a
    ///   per-kind callsite and paying to re-author the diagnostic list.
    /// - An operator-facing "boundary is MISSING [JobAttested,
    ///   ClosedLoopAuth]" audit dump reads
    ///   `boundary.postconditions.missing_kinds()` directly at ONE call
    ///   site rather than restating the negated closed-set walk at
    ///   every consumer.
    /// - A fleet-wide gap analysis ("which processes are missing a
    ///   `ClosedLoopAuth` postcondition") reaches this ONE primitive
    ///   through `spec.boundary.postconditions.missing_kinds()
    ///   .contains(&ConditionKind::ClosedLoopAuth)` rather than paying
    ///   for the negated `.has_kind` sweep at every callsite.
    /// - A hypothetical `condition-kinds-missing-<n>` require-tag
    ///   classifier prefix family that publishes the missing-set
    ///   cardinality as a scalar reads
    ///   [`Self::missing_kind_count`] (the scalar-cardinality peer of
    ///   this widened primitive) without allocating.
    ///
    /// # Theory grounding
    ///
    /// - THEORY.md §II.1 invariant 5 — composition preserves proofs.
    ///   The closed-set complement lives at ONE substrate site as a
    ///   typed projection of [`Self::has_kind`] over the closed set
    ///   [`ConditionKind::ALL`] under negation. Every downstream gap-
    ///   analysis consumer binds through the SAME shape rather than
    ///   restating the negated ALL-filter closure body.
    /// - THEORY.md §VI.1 — generation over composition. A new
    ///   [`ConditionKind`] variant added to `ALL` reaches this
    ///   primitive mechanically (the closed-set walk picks up the new
    ///   entry on the missing side WITHOUT further per-caller edit —
    ///   any slice that doesn't yet populate the new kind sees it
    ///   listed as missing at every downstream callsite).
    fn missing_kinds(&self) -> Vec<ConditionKind> {
        self.iter_missing_kinds().collect()
    }

    /// Zero-allocation iterator peer of [`Self::missing_kinds`] — walk
    /// [`ConditionKind::ALL`] in canonical order and yield every
    /// [`ConditionKind`] whose corresponding slot on this slice is EMPTY
    /// (no [`Condition`] in the slice carries that kind), WITHOUT
    /// materializing an intermediate [`Vec<ConditionKind>`].
    ///
    /// Default body:
    /// `ConditionKind::ALL.iter().copied().filter(|&k| !self.has_kind(k))`.
    /// The composition law
    /// `missing_kinds() == iter_missing_kinds().collect::<Vec<_>>()`
    /// holds by construction — [`Self::missing_kinds`]'s default body IS
    /// `self.iter_missing_kinds().collect()`, so a caller that overrides
    /// the widened Vec primitive with a divergent walk simultaneously
    /// drifts both surfaces (surfacing at the substrate testkit
    /// [`assert_slice_refinement_composition_laws`] which pins the Vec
    /// projection equals `iter().collect()`).
    ///
    /// # Sibling to [`Self::missing_kinds`] / [`Self::missing_kind_count`]
    ///
    /// Load-bearing iterator peer of the slice-level closed-set-complement
    /// axis — where `missing_kinds` returns the SET (heap-allocated `Vec`,
    /// canonical `ConditionKind::ALL` order) and `missing_kind_count`
    /// scalar-projects its cardinality, `iter_missing_kinds` opens the
    /// walk as a `Copy` iterator so consumers that need a short-
    /// circuiting fold avoid the intermediate allocation entirely.
    ///
    /// # Peer to [`Self::iter_distinct_kinds`]
    ///
    /// Closed-set-COMPLEMENT peer under a NEGATED point-probe. The two
    /// iterators PARTITION `ConditionKind::ALL`:
    /// `iter_distinct_kinds().chain(iter_missing_kinds()).collect::<HashSet<_>>()`
    /// equals `ConditionKind::ALL.iter().copied().collect()`, and the two
    /// iterators yield disjoint element sets.
    ///
    /// # Peer to [`crate::tagged_union::TaggedUnion::iter_missing_kinds`]
    ///
    /// Same shape at the peer axis one struct layer up: where
    /// `iter_missing_kinds` on the tagged-union parent opens the closed-
    /// set-complement walk under a negated `has` point-probe, this method
    /// opens the SAME walk on the slice-level presence-probe axis under a
    /// negated `has_kind` point-probe. Both close the "load-bearing
    /// iterator on the complement side" refinement at two adjacent
    /// typescape sites through the SAME
    /// `<CLOSED_SET>::ALL.iter().copied().filter(|&k| !has_probe(k))`
    /// composition body.
    ///
    /// # Compounding future consumers
    ///
    /// - Every scalar closed-set-complement peer already at the trait
    ///   (`missing_kind_count`, `first_missing_kind`, `last_missing_kind`,
    ///   `unique_missing_kind`, `is_kind_saturated`,
    ///   `has_any_missing_kind`, `has_unique_missing_kind`,
    ///   `has_multiple_missing_kinds`, `has_at_most_one_missing_kind`)
    ///   folds a specialization of
    ///   `ConditionKind::ALL.iter().filter(|k| !self.has_kind(**k))` —
    ///   they can compose over `iter_missing_kinds()` at ONE substrate
    ///   site rather than restating the closed-set walk body per peer.
    /// - A downstream diagnostic composer (an operator-facing "still
    ///   missing: [{}]" message that streams the label list into a
    ///   `write!` buffer on the partially-populated arm) reads
    ///   `slice.iter_missing_kinds().map(|k| k.label())` and folds through
    ///   `itertools::join` without the allocation `Vec<ConditionKind> ->
    ///   String` pays.
    ///
    /// # Theory grounding
    ///
    /// - THEORY.md §II.1 invariant 5 — composition preserves proofs.
    ///   The load-bearing iterator projection on the complement side
    ///   lives at ONE substrate site, byte-for-byte symmetrical with
    ///   [`Self::iter_distinct_kinds`] under a negated `has_kind`
    ///   predicate.
    /// - THEORY.md §VI.1 — generation over composition. A new
    ///   [`ConditionKind`] variant added to `ALL` reaches the walk
    ///   mechanically (the closed-set filter picks up the new entry on
    ///   the missing side) and every downstream fold sees the wider
    ///   complement without further per-caller edit.
    fn iter_missing_kinds(&self) -> impl Iterator<Item = ConditionKind> + '_ {
        ConditionKind::ALL
            .iter()
            .copied()
            .filter(|&k| !self.has_kind(k))
    }

    /// Scalar cardinality projection of [`Self::missing_kinds`] onto its
    /// `.len()` — the number of [`ConditionKind`] variants that do NOT
    /// appear in this slice. Default body:
    /// `ConditionKind::ALL.iter().filter(|k| !self.has_kind(**k)).count()`
    /// — a closed-set walk composed against [`Self::has_kind`] per variant
    /// under a NEGATED point-probe, WITHOUT materializing the intermediate
    /// `Vec<ConditionKind>` a caller reaching only for the scalar
    /// cardinality otherwise pays for. An empty slice returns
    /// `ConditionKind::ALL.len()` (every kind is missing); a slice
    /// carrying every variant returns `0` (no kind is missing).
    ///
    /// # Sibling to [`Self::missing_kinds`] / [`Self::distinct_kind_count`]
    ///
    /// Scalar projection of the closed-set-complement widened primitive
    /// — where `missing_kinds` returns the SET (a `Vec<ConditionKind>`
    /// in canonical [`ConditionKind::ALL`] order), `missing_kind_count`
    /// collapses that set to its cardinality. The composition law
    /// `missing_kind_count() == missing_kinds().len()` binds the scalar
    /// projection to the widened primitive at the trait's default body
    /// and is swept substrate-wide by
    /// [`assert_slice_refinement_composition_laws`] as its scalar-
    /// cardinality-complement arm.
    ///
    /// Byte-for-byte peer of [`Self::distinct_kind_count`] one axis over
    /// (under a negated `has_kind` predicate): where `distinct_kind_count`
    /// scalar-projects the closed-set-INVERSION widened primitive
    /// `distinct_kinds`, this method scalar-projects the closed-set-
    /// COMPLEMENT widened primitive `missing_kinds`. The two scalar
    /// projections PARTITION the closed-set cardinality:
    /// `distinct_kind_count() + missing_kind_count() ==
    /// ConditionKind::ALL.len()` — the scalar consequence of the
    /// `(distinct_kinds, missing_kinds)` partition law that
    /// [`assert_slice_refinement_composition_laws`] pins at the
    /// widened-primitive layer.
    ///
    /// # Peer to [`crate::tagged_union::TaggedUnion::populated_kind_count`]'s
    /// hypothetical complement peer
    ///
    /// Same shape at the peer axis one struct layer up: fixing the
    /// slice-side carrier and inverting the presence probe over the
    /// closed set under a negated predicate. The two primitives close
    /// the "closed-set-complement scalar cardinality" refinement at
    /// two adjacent typescape sites — one per closed-set-addressed
    /// slice-level refinement (this primitive), one per closed-set-
    /// addressed tagged-union parent-level refinement (a symmetric
    /// future addition).
    ///
    /// # Compounding future consumers
    ///
    /// - A future coherence check that enforces "every process boundary
    ///   carries EVERY [`ConditionKind`] under some slot" now reads
    ///   `spec.boundary.postconditions.missing_kind_count() == 0` at
    ///   ONE call site rather than paying for
    ///   `spec.boundary.postconditions.missing_kinds().is_empty()`
    ///   (with its intermediate heap allocation) or the eight-way
    ///   negated sweep with `has_kind` at the callsite.
    /// - A future require-tag classifier arm that surfaces the missing-
    ///   set cardinality as a scalar (the exact
    ///   `condition-kinds-missing-<n>` require-tag classifier prefix
    ///   family called out in [`Self::missing_kinds`]'s doc-comment as
    ///   a hypothetical compounding-future consumer) reaches this ONE
    ///   primitive without allocating.
    /// - A future gap-analysis dashboard reporting "boundary is missing
    ///   N of {N_TOTAL} distinct kinds" reaches
    ///   `slice.missing_kind_count()` directly rather than restating the
    ///   negated `.iter().filter(...).count()` closure body.
    ///
    /// # Theory grounding
    ///
    /// - THEORY.md §II.1 invariant 5 — composition preserves proofs.
    ///   The scalar cardinality lives at ONE substrate site as a typed
    ///   projection of [`Self::missing_kinds`] onto its `.len()`, and
    ///   the default body composes against [`Self::has_kind`] over the
    ///   closed set [`ConditionKind::ALL`] under negation byte-
    ///   identically to `missing_kinds` without the intermediate `Vec`.
    ///   Every downstream aggregate consumer binds through the SAME
    ///   shape rather than paying for the allocation to reach the
    ///   cardinality.
    /// - THEORY.md §VI.1 — generation over composition. A new
    ///   [`ConditionKind`] variant added to `ALL` reaches this primitive
    ///   mechanically (the closed-set walk picks up the new entry on
    ///   the missing side WITHOUT further per-caller edit — any slice
    ///   that doesn't yet populate the new kind sees the cardinality
    ///   rise by one at every downstream callsite).
    fn missing_kind_count(&self) -> usize {
        self.iter_missing_kinds().count()
    }

    /// Short-circuiting `Option<ConditionKind>` peer of
    /// [`Self::distinct_kinds`] — the FIRST [`ConditionKind`] variant
    /// present in this slice, in canonical [`ConditionKind::ALL`] order,
    /// or `None` when the slice carries no matching kind. Default body:
    /// `ConditionKind::ALL.iter().copied().find(|k| self.has_kind(*k))`
    /// — a closed-set walk composed against [`Self::has_kind`] per
    /// variant that SHORT-CIRCUITS at the earliest match.
    ///
    /// # Sibling to [`Self::distinct_kinds`] / [`Self::distinct_kind_count`]
    ///
    /// Third refinement on the closed-set-inversion axis, `Option<ConditionKind>`-
    /// valued: `distinct_kinds` returns the SET, `distinct_kind_count`
    /// scalar-projects the cardinality, and `first_distinct_kind`
    /// scalar-projects the SET onto its earliest element. The composition
    /// law `first_distinct_kind() == distinct_kinds().first().copied()`
    /// binds the earliest-element projection to the widened primitive at
    /// the trait's default body — pinned substrate-wide by
    /// [`assert_slice_refinement_composition_laws`] as its
    /// earliest-element-inversion arm. Both coarser projections agree on
    /// emptiness: `first_distinct_kind().is_none() ==
    /// (distinct_kind_count() == 0)`.
    ///
    /// # Peer to [`crate::tagged_union::TaggedUnion::first_populated_kind`]
    ///
    /// Same shape at the peer axis one struct layer up: fixing the
    /// carrier and short-circuiting on the earliest [`ConditionKind::ALL`]
    /// hit under [`Self::has_kind`]. `TaggedUnion::first_populated_kind`
    /// walks the tagged-union parent's closed set; `first_distinct_kind`
    /// here walks [`ConditionKind::ALL`] on the slice-level presence-probe
    /// axis. The two primitives close the "earliest-element scalar-
    /// projection of the closed-set-inversion widened primitive"
    /// refinement at two adjacent typescape sites — one per closed-set-
    /// addressed slice-level refinement (this primitive), one per closed-
    /// set-addressed tagged-union parent-level refinement.
    ///
    /// # Semantics
    ///
    /// Returns `Some(k)` where `k` is the earliest [`ConditionKind::ALL`]
    /// entry with `self.has_kind(k) == true`, or `None` when no kind is
    /// present. An empty slice returns `None`. A slice carrying multiple
    /// variants returns the earliest one in [`ConditionKind::ALL`] order
    /// — a strictly more informative projection than
    /// `distinct_kinds().first().copied()` without materializing the
    /// intermediate `Vec<ConditionKind>` the widened primitive
    /// otherwise pays for.
    ///
    /// # Compounding future consumers
    ///
    /// - An operator-facing "first present kind" diagnostic on an audit
    ///   dump that names ONE kind rather than the full set reaches this
    ///   ONE substrate site rather than paying for
    ///   `slice.distinct_kinds().first().copied()` (with its
    ///   intermediate heap allocation).
    /// - A `first-distinct-<kind>` require-tag classifier arm reads this
    ///   primitive with no allocation, byte-for-byte symmetrical with
    ///   `slice.has_kind(kind)` under a closed-set-inversion projection.
    /// - A fast-path branch that discriminates "empty" from "any
    ///   populated" reads `slice.first_distinct_kind().is_some()` at ONE
    ///   call site rather than allocating a `Vec<ConditionKind>` through
    ///   `!distinct_kinds().is_empty()` or paying for the full
    ///   `distinct_kind_count() > 0` walk.
    ///
    /// # Theory grounding
    ///
    /// - THEORY.md §II.1 invariant 5 — composition preserves proofs. The
    ///   earliest-element projection lives at ONE substrate site as a
    ///   typed projection of [`Self::has_kind`] over the closed set
    ///   [`ConditionKind::ALL`] under short-circuit walk semantics.
    /// - THEORY.md §VI.1 — generation over composition. A new
    ///   [`ConditionKind`] variant added to `ALL` reaches this primitive
    ///   mechanically (the closed-set walk picks up the new entry) —
    ///   every downstream consumer sees the wider earliest-hit projection
    ///   without further per-caller edit.
    fn first_distinct_kind(&self) -> Option<ConditionKind> {
        self.iter_distinct_kinds().next()
    }

    /// Short-circuiting `Option<ConditionKind>` peer of
    /// [`Self::missing_kinds`] — the FIRST [`ConditionKind`] variant
    /// ABSENT from this slice, in canonical [`ConditionKind::ALL`] order,
    /// or `None` when the slice carries every variant. Default body:
    /// `ConditionKind::ALL.iter().copied().find(|k| !self.has_kind(*k))`
    /// — a closed-set walk composed against [`Self::has_kind`] per
    /// variant under NEGATION with SHORT-CIRCUIT at the earliest empty
    /// slot.
    ///
    /// # Sibling to [`Self::missing_kinds`] / [`Self::missing_kind_count`]
    ///
    /// Third refinement on the closed-set-complement axis,
    /// `Option<ConditionKind>`-valued: `missing_kinds` returns the SET,
    /// `missing_kind_count` scalar-projects the cardinality, and
    /// `first_missing_kind` scalar-projects the SET onto its earliest
    /// element. The composition law
    /// `first_missing_kind() == missing_kinds().first().copied()` binds
    /// the earliest-element projection to the widened primitive at the
    /// trait's default body — pinned substrate-wide by
    /// [`assert_slice_refinement_composition_laws`] as its
    /// earliest-element-complement arm. Both coarser projections agree
    /// on saturation: `first_missing_kind().is_none() ==
    /// (missing_kind_count() == 0)`.
    ///
    /// # Peer to [`Self::first_distinct_kind`]
    ///
    /// Closed-set-complement peer of the closed-set-inversion earliest-
    /// element primitive under a negated `has_kind` predicate. The two
    /// primitives PARTITION [`ConditionKind::ALL`]'s earliest-element
    /// projection: at least one of `first_distinct_kind()` and
    /// `first_missing_kind()` is `Some` on any non-degenerate closed set
    /// (both are `Some` iff `1 ≤ distinct_kind_count() <
    /// ConditionKind::ALL.len()`; only the distinct-side is `Some` on a
    /// saturated slice; only the missing-side is `Some` on an empty
    /// slice).
    ///
    /// # Peer to [`crate::tagged_union::TaggedUnion::first_missing_kind`]
    ///
    /// Same shape at the peer axis one struct layer up under a negated
    /// predicate. The two primitives close the "earliest-element scalar-
    /// projection of the closed-set-complement widened primitive"
    /// refinement at two adjacent typescape sites — one per closed-set-
    /// addressed slice-level refinement (this primitive), one per closed-
    /// set-addressed tagged-union parent-level refinement.
    ///
    /// # Semantics
    ///
    /// An empty slice returns `Some(ConditionKind::ALL[0])` (every kind
    /// missing, first hit is index 0). A slice populating exactly `k`
    /// returns `Some(ConditionKind::ALL[0])` if `k != ALL[0]`, else
    /// `Some(ALL[1])` (the earliest non-`k` entry). A saturated slice
    /// carrying every variant returns `None`.
    ///
    /// # Compounding future consumers
    ///
    /// - An operator-facing "first still-unfilled kind" diagnostic on a
    ///   partially-populated boundary reads
    ///   `boundary.postconditions.first_missing_kind()` at ONE substrate
    ///   site — a strictly-more-informative projection than
    ///   `!has_kind(JobAttested)` at a per-kind callsite for a fleet-wide
    ///   "which processes are missing at least one closed-loop kind"
    ///   audit.
    /// - A `first-missing-<kind>` require-tag classifier arm reads this
    ///   primitive with no allocation, byte-for-byte symmetrical with
    ///   `slice.first_distinct_kind()`.
    /// - A fast-path branch that discriminates "saturated" from "at least
    ///   one missing" reads `slice.first_missing_kind().is_some()` at ONE
    ///   call site rather than allocating through
    ///   `!missing_kinds().is_empty()` or paying for the full
    ///   `missing_kind_count() > 0` walk.
    ///
    /// # Theory grounding
    ///
    /// - THEORY.md §II.1 invariant 5 — composition preserves proofs. The
    ///   complement-earliest-element projection lives at ONE substrate
    ///   site as a typed projection of [`Self::has_kind`] over the
    ///   closed set [`ConditionKind::ALL`] under negation with short-
    ///   circuit walk semantics.
    /// - THEORY.md §VI.1 — generation over composition. A new
    ///   [`ConditionKind`] variant added to `ALL` reaches this primitive
    ///   mechanically (the closed-set walk picks up the new entry on the
    ///   missing side) — every downstream consumer sees the wider
    ///   complement's earliest hit without further per-caller edit.
    fn first_missing_kind(&self) -> Option<ConditionKind> {
        self.iter_missing_kinds().next()
    }

    /// Short-circuiting `Option<ConditionKind>` peer of
    /// [`Self::distinct_kinds`] — the LAST [`ConditionKind`] variant
    /// present in this slice, in canonical [`ConditionKind::ALL`]
    /// order, or `None` when the slice carries no variant. Default
    /// body: `ConditionKind::ALL.iter().rev().copied().find(|k|
    /// self.has_kind(*k))` — a REVERSED closed-set walk composed
    /// against [`Self::has_kind`] per variant that SHORT-CIRCUITS at
    /// the latest hit.
    ///
    /// # Sibling to [`Self::distinct_kinds`] /
    /// [`Self::distinct_kind_count`] / [`Self::first_distinct_kind`]
    ///
    /// Fourth refinement on the closed-set-inversion axis and second
    /// scalar `Option<ConditionKind>` projection: `distinct_kinds`
    /// returns the SET, `distinct_kind_count` scalar-projects the
    /// cardinality, `first_distinct_kind` scalar-projects the SET
    /// onto its earliest element, and `last_distinct_kind` scalar-
    /// projects the SET onto its latest element. The composition law
    /// `last_distinct_kind() == distinct_kinds().last().copied()`
    /// binds the latest-element projection to the widened primitive
    /// at the trait's default body — pinned substrate-wide by
    /// [`assert_slice_refinement_composition_laws`] as its
    /// latest-element-inversion arm. Both scalar projections agree on
    /// emptiness: `last_distinct_kind().is_none() ==
    /// first_distinct_kind().is_none() == distinct_kinds().is_empty()`.
    ///
    /// # Peer to [`Self::first_distinct_kind`]
    ///
    /// Time-reversed peer under the SAME `has_kind` predicate: where
    /// `first_distinct_kind` walks [`ConditionKind::ALL`] forward and
    /// SHORT-CIRCUITS at the earliest hit, this primitive walks the
    /// SAME closed set in reverse and SHORT-CIRCUITS at the latest
    /// hit. The two primitives close the "endpoint scalar-projection
    /// of the closed-set-inversion widened primitive" refinement pair
    /// at one substrate site — one per endpoint. On a slice with
    /// exactly one distinct kind both projections agree; on a slice
    /// with distinct-kind-count ≥ 2 they yield distinct results
    /// (the earliest and latest elements of the closed-set-inversion
    /// respectively).
    ///
    /// # Semantics
    ///
    /// An empty slice returns `None` (no kind present, no hit on any
    /// walk direction). A slice populating exactly `k` returns
    /// `Some(k)` (single hit; earliest = latest). A saturated slice
    /// carrying every variant returns `Some(ConditionKind::ALL.last()
    /// .unwrap())` (the last ALL entry hits at the earliest walk step
    /// of the reversed walk).
    ///
    /// # Compounding future consumers
    ///
    /// - A `last-distinct-<kind>` require-tag classifier arm reads
    ///   the latest-populated kind through this ONE substrate
    ///   primitive with no allocation, byte-for-byte symmetrical with
    ///   the earliest-hit `slice.first_distinct_kind()` peer.
    /// - A future coherence check that surfaces "boundary ends with
    ///   ClosedLoopAuth" reads
    ///   `spec.boundary.postconditions.last_distinct_kind() ==
    ///   Some(ConditionKind::ClosedLoopAuth)` at ONE call site rather
    ///   than paying for `spec.boundary.postconditions
    ///   .distinct_kinds().last() == Some(&…)` with its intermediate
    ///   heap allocation.
    /// - Combined with [`Self::first_distinct_kind`], operator
    ///   diagnostics that render a "populated-kind range" summary
    ///   (`first..=last` on the closed-set-inversion projection) read
    ///   the two endpoints through TWO substrate primitives at
    ///   symmetric shapes without allocating.
    ///
    /// # Theory grounding
    ///
    /// - THEORY.md §II.1 invariant 5 — composition preserves proofs.
    ///   The latest-element projection lives at ONE substrate site as
    ///   a typed projection of [`Self::has_kind`] over the closed set
    ///   [`ConditionKind::ALL`] under REVERSED short-circuit walk
    ///   semantics; byte-for-byte peer of the earliest-element
    ///   projection under FORWARD walk semantics.
    /// - THEORY.md §VI.1 — generation over composition. A new
    ///   [`ConditionKind`] variant added to `ALL` reaches this
    ///   primitive mechanically (the reversed closed-set walk picks
    ///   up the new entry at the appropriate position) — every
    ///   downstream consumer sees the wider latest-hit projection
    ///   without further per-caller edit.
    fn last_distinct_kind(&self) -> Option<ConditionKind> {
        self.iter_distinct_kinds().last()
    }

    /// Short-circuiting `Option<ConditionKind>` peer of
    /// [`Self::missing_kinds`] — the LAST [`ConditionKind`] variant
    /// ABSENT from this slice, in canonical [`ConditionKind::ALL`]
    /// order, or `None` when the slice carries every variant. Default
    /// body: `ConditionKind::ALL.iter().rev().copied().find(|k|
    /// !self.has_kind(*k))` — a REVERSED closed-set walk composed
    /// against [`Self::has_kind`] per variant under NEGATION with
    /// SHORT-CIRCUIT at the latest empty slot.
    ///
    /// # Sibling to [`Self::missing_kinds`] /
    /// [`Self::missing_kind_count`] / [`Self::first_missing_kind`]
    ///
    /// Fourth refinement on the closed-set-complement axis and second
    /// scalar `Option<ConditionKind>` projection: `missing_kinds`
    /// returns the SET, `missing_kind_count` scalar-projects the
    /// cardinality, `first_missing_kind` scalar-projects the SET onto
    /// its earliest element, and `last_missing_kind` scalar-projects
    /// the SET onto its latest element. The composition law
    /// `last_missing_kind() == missing_kinds().last().copied()` binds
    /// the latest-element projection to the widened primitive at the
    /// trait's default body — pinned substrate-wide by
    /// [`assert_slice_refinement_composition_laws`] as its
    /// latest-element-complement arm. Both scalar projections agree
    /// on saturation: `last_missing_kind().is_none() ==
    /// first_missing_kind().is_none() == missing_kinds().is_empty()`.
    ///
    /// # Peer to [`Self::first_missing_kind`]
    ///
    /// Time-reversed peer under the SAME negated `has_kind` predicate:
    /// where `first_missing_kind` walks [`ConditionKind::ALL`] forward
    /// under negation and SHORT-CIRCUITS at the earliest empty slot,
    /// this primitive walks the SAME closed set in reverse and SHORT-
    /// CIRCUITS at the latest empty slot. The two primitives close
    /// the "endpoint scalar-projection of the closed-set-complement
    /// widened primitive" refinement pair at one substrate site.
    ///
    /// # Peer to [`Self::last_distinct_kind`]
    ///
    /// Closed-set-complement peer of the closed-set-inversion latest-
    /// element primitive under a NEGATED `has_kind` predicate. Along
    /// with [`Self::first_distinct_kind`] and [`Self::first_missing_kind`]
    /// the four scalar-endpoint projections partition the endpoint
    /// axis into (present, absent) × (earliest, latest) — every
    /// endpoint-addressable coherence check reads ONE of the four at
    /// ONE call site, never the full `Vec<ConditionKind>` walk.
    ///
    /// # Semantics
    ///
    /// An empty slice returns `Some(ConditionKind::ALL.last().unwrap())`
    /// (every kind missing, latest hit is the last ALL entry). A slice
    /// populating exactly `k` returns `Some(ALL.last().unwrap())` if
    /// `k != ALL.last().unwrap()`, else `Some(ALL[ALL.len() - 2])` (the
    /// latest non-`k` entry). A saturated slice carrying every variant
    /// returns `None`.
    ///
    /// # Compounding future consumers
    ///
    /// - An operator-facing "last still-unfilled kind" diagnostic on a
    ///   partially-populated boundary reads
    ///   `boundary.postconditions.last_missing_kind()` at ONE substrate
    ///   site — a strictly-more-informative projection than
    ///   `!has_kind(ClosedLoopAuth)` at a per-kind callsite for a
    ///   fleet-wide "which processes are latest-missing a specific
    ///   closed-loop kind" audit.
    /// - A `last-missing-<kind>` require-tag classifier arm reads this
    ///   primitive with no allocation, byte-for-byte symmetrical with
    ///   the earliest-hit `slice.first_missing_kind()` peer.
    /// - Combined with [`Self::first_missing_kind`], a coherence check
    ///   that renders a "missing-kind range" summary reads the two
    ///   endpoints through TWO substrate primitives at symmetric
    ///   shapes without allocating through `missing_kinds()`.
    ///
    /// # Theory grounding
    ///
    /// - THEORY.md §II.1 invariant 5 — composition preserves proofs.
    ///   The complement-latest-element projection lives at ONE
    ///   substrate site as a typed projection of [`Self::has_kind`]
    ///   over the closed set [`ConditionKind::ALL`] under negation
    ///   with REVERSED short-circuit walk semantics; byte-for-byte
    ///   peer of the complement-earliest-element projection under
    ///   FORWARD walk semantics.
    /// - THEORY.md §VI.1 — generation over composition. A new
    ///   [`ConditionKind`] variant added to `ALL` reaches this
    ///   primitive mechanically (the reversed closed-set walk picks
    ///   up the new entry on the missing side at the appropriate
    ///   position) — every downstream consumer sees the wider
    ///   complement's latest hit without further per-caller edit.
    fn last_missing_kind(&self) -> Option<ConditionKind> {
        self.iter_missing_kinds().last()
    }

    /// Boolean saturation predicate on the closed-set-inversion axis —
    /// `true` iff EVERY [`ConditionKind::ALL`] variant appears at least
    /// once in this slice (equivalently, [`Self::missing_kinds`] is
    /// empty).
    ///
    /// Default body:
    /// `ConditionKind::ALL.iter().all(|k| self.has_kind(*k))` — a
    /// SHORT-CIRCUITING closed-set walk composed against [`Self::has_kind`]
    /// per variant that returns `false` at the FIRST missing kind,
    /// WITHOUT materializing [`Self::missing_kinds`]'s `Vec` and WITHOUT
    /// walking every entry to build [`Self::missing_kind_count`]'s
    /// scalar. Strictly cheaper than either widened primitive on every
    /// partially-populated arm (returns at the first empty slot rather
    /// than sweeping the full closed set).
    ///
    /// # Peer to [`crate::tagged_union::TaggedUnion::is_saturated`]
    ///
    /// Slice-level peer of the tagged-union parent-level saturation
    /// predicate one struct-layer up: where `is_saturated` names the
    /// tagged-union arm where every `<Self::Kind as ClosedSet>::ALL`
    /// slot is populated, `is_kind_saturated` names the slice arm where
    /// every [`ConditionKind::ALL`] variant appears at least once. Both
    /// short-circuit at the first missing entry under the SAME
    /// `<CLOSED_SET>::ALL.iter().all(has)` walk shape at two adjacent
    /// typescape sites.
    ///
    /// # Sibling to [`Self::missing_kind_count`] / [`Self::missing_kinds`]
    ///
    /// Boolean cardinality-endpoint peer of the scalar cardinality
    /// primitive on the closed-set-complement axis — where
    /// `missing_kind_count` returns the FULL scalar (any `usize` in
    /// `0..=ConditionKind::ALL.len()`), `is_kind_saturated` collapses
    /// that scalar to its zero-arm Boolean projection. The composition
    /// law `is_kind_saturated() == (missing_kind_count() == 0)` binds
    /// the Boolean projection to the scalar primitive at the trait's
    /// default body — swept substrate-wide by
    /// [`assert_slice_refinement_composition_laws`] as its
    /// saturation-endpoint arm.
    ///
    /// # Semantics
    ///
    /// An empty slice returns `false` (no kind is populated). A slice
    /// carrying a strict subset of [`ConditionKind::ALL`] returns
    /// `false`. A slice that carries every variant at least once
    /// (multiplicity is irrelevant) returns `true` — the SOLE arm
    /// where `is_kind_saturated` returns `true`.
    ///
    /// # Compounding future consumers
    ///
    /// - A future coherence check that enforces "every process boundary
    ///   exhaustively covers every [`ConditionKind`]" reads
    ///   `boundary.postconditions.is_kind_saturated()` at ONE call site
    ///   — one short-circuit walk, no allocation, no scalar equality
    ///   comparison against `ConditionKind::ALL.len()`.
    /// - An `is-kind-saturated` require-tag classifier arm reaches this
    ///   primitive with no allocation, byte-for-byte peer of the
    ///   tagged-union `is-saturated` classifier one struct-layer up.
    /// - A fleet-wide gap-analysis dashboard fast-path that discriminates
    ///   "boundary spans every kind" from "boundary is missing some
    ///   kind" reads `boundary.postconditions.is_kind_saturated()` at
    ///   ONE call site rather than restating either
    ///   `boundary.postconditions.missing_kind_count() == 0` (which
    ///   walks every slot to count) or
    ///   `boundary.postconditions.missing_kinds().is_empty()` (which
    ///   allocates the Vec before the emptiness check).
    ///
    /// # Theory grounding
    ///
    /// - THEORY.md §II.1 invariant 5 — composition preserves proofs.
    ///   The saturation-endpoint projection lives at ONE substrate
    ///   site as a typed short-circuiting closed-set walk
    ///   `ConditionKind::ALL.iter().all(has_kind)`. Every downstream
    ///   consumer binds through the SAME shape rather than restating
    ///   the `== ConditionKind::ALL.len()` scalar composition body.
    /// - THEORY.md §VI.1 — generation over composition. A new
    ///   [`ConditionKind`] variant added to `ALL` reaches this
    ///   primitive mechanically through the `all` short-circuit — a
    ///   slice that was previously saturated is no longer saturated
    ///   at every downstream callsite unless it also carries the new
    ///   variant.
    fn is_kind_saturated(&self) -> bool {
        self.iter_missing_kinds().next().is_none()
    }

    /// Boolean cardinality zero-endpoint peer of [`Self::is_kind_saturated`]
    /// on the closed-set-inversion axis — `true` iff NO
    /// [`ConditionKind::ALL`] variant appears in this slice (equivalently,
    /// [`Self::distinct_kinds`] is empty, [`Self::distinct_kind_count`]
    /// `== 0`, and [`Self::first_distinct_kind`] is [`None`]).
    ///
    /// Default body: `self.iter_distinct_kinds().next().is_none()` — a
    /// SHORT-CIRCUITING closed-set walk composed against the load-bearing
    /// distinct iterator that returns `true` iff the first hit is [`None`],
    /// WITHOUT materializing [`Self::distinct_kinds`]'s `Vec`, WITHOUT
    /// walking every slot to build [`Self::distinct_kind_count`]'s scalar,
    /// and WITHOUT allocating the closed-set-inversion scan. Strictly
    /// cheaper than either widened primitive on every arm because the
    /// walk short-circuits at the first present kind on the has-side
    /// walk rather than paying for the Vec allocation or the full
    /// cardinality count.
    ///
    /// # Peer to [`crate::tagged_union::TaggedUnion::is_empty`]
    ///
    /// Slice-level peer of the tagged-union parent-level zero-endpoint
    /// predicate one struct-layer up: where
    /// [`crate::tagged_union::TaggedUnion::is_empty`] answers "is EVERY
    /// slot on the tagged-union parent empty?", `is_kind_empty` answers
    /// "does NO kind appear in ANY condition of the slice?". Both
    /// short-circuit at the first present entry under the SAME
    /// `<CLOSED_SET>::ALL.iter().any(has)`-then-negate walk shape at two
    /// adjacent typescape sites — the two primitives close the zero-
    /// endpoint on the closed-set-inversion axis at both struct layers
    /// under the SAME shape.
    ///
    /// # Sibling to [`Self::is_kind_saturated`]
    ///
    /// Axis-parity mirror of the closed-set-complement saturation-
    /// endpoint primitive on the closed-set-inversion axis — where
    /// `is_kind_saturated` returns `true` iff `missing_kind_count == 0`
    /// (every kind PRESENT), `is_kind_empty` returns `true` iff
    /// `distinct_kind_count == 0` (every kind ABSENT). Together the two
    /// Booleans name the (empty, saturated) endpoints of the
    /// (distinct, missing) partition: a slice is EMPTY iff
    /// `is_kind_empty()` returns `true` (equivalently, `is_kind_saturated
    /// == false` AND no partial-populated arm applies); a slice is
    /// SATURATED iff `is_kind_saturated()` returns `true`. On any `N ≥ 1`
    /// closed set, at most ONE of the two returns `true`; on `N == 0`
    /// closed sets both return `true` vacuously. Byte-for-byte peer of
    /// the tagged-union `is_empty` / `is_saturated` sibling pair one
    /// struct-layer up.
    ///
    /// # Sibling to [`Self::has_any_distinct_kind`]
    ///
    /// Boolean zero-endpoint peer of the at-least-one halfspace primitive
    /// on the closed-set-inversion axis — where `has_any_distinct_kind`
    /// returns `true` iff at least one kind is PRESENT, `is_kind_empty`
    /// returns its Boolean-negation: `true` iff `distinct_kind_count == 0`.
    /// Together the two Booleans partition the distinct-cardinality
    /// closed set: exactly one of `is_kind_empty()` and
    /// `has_any_distinct_kind()` is `true` for every slice. The
    /// definitional negation law `is_kind_empty() == !has_any_distinct_kind()`
    /// is pinned as a first-class typed invariant by
    /// [`assert_slice_refinement_composition_laws`] as its zero-endpoint
    /// arm on the distinct axis, byte-for-byte peer of the missing-axis
    /// pin `has_any_missing_kind() == !is_kind_saturated()`.
    ///
    /// # Sibling to [`Self::distinct_kinds`] / [`Self::distinct_kind_count`]
    ///
    /// Boolean zero-endpoint peer of the widened + scalar closed-set-
    /// inversion primitives — where `distinct_kinds` returns the FULL
    /// distinct SET and `distinct_kind_count` returns its cardinality,
    /// `is_kind_empty` collapses either the widened primitive to its
    /// emptiness Boolean or the scalar to its `== 0` cardinality-endpoint
    /// Boolean. The composition laws
    /// `is_kind_empty() == distinct_kinds().is_empty()` and
    /// `is_kind_empty() == (distinct_kind_count() == 0)` bind this
    /// Boolean projection to the widened + scalar primitives at the
    /// trait's default body — strictly cheaper than either widened
    /// primitive on every non-empty arm because the walk short-circuits
    /// at the first present kind rather than allocating the closed-set-
    /// inversion scan or walking every slot to build the scalar
    /// cardinality.
    ///
    /// # Semantics
    ///
    /// An empty slice returns `true` — the SOLE arm where `is_kind_empty`
    /// returns `true` on any `N ≥ 1` closed set, byte-for-byte peer of
    /// the SOLE arm where `is_kind_saturated` returns `true` (a slice
    /// carrying every variant at least once). A slice carrying a strict
    /// subset of [`ConditionKind::ALL`] returns `false`. A saturated
    /// slice returns `false` on `N ≥ 1` closed sets. Multiplicity is
    /// irrelevant on both sides — the predicate collapses to the
    /// distinct-set's emptiness.
    ///
    /// # Compounding future consumers
    ///
    /// - A fleet-wide "no coverage at all" fast-path that discriminates
    ///   "the slice is empty" from "the slice carries at least one kind"
    ///   reads `boundary.postconditions.is_kind_empty()` at ONE call site
    ///   rather than restating `distinct_kind_count() == 0` (which walks
    ///   every slot to count), `distinct_kinds().is_empty()` (which
    ///   allocates the Vec before the emptiness check), or negating
    ///   `has_any_distinct_kind()` at the callsite.
    /// - An `is-kind-empty` require-tag classifier arm reaches this
    ///   primitive with no allocation, byte-for-byte peer of the
    ///   tagged-union `is-empty` classifier one struct-layer up under
    ///   the SAME zero-endpoint short-circuit shape.
    /// - A coherence check that flags "any process boundary whose
    ///   postcondition slice is empty" reads
    ///   `boundary.postconditions.is_kind_empty()` at ONE substrate
    ///   primitive per test rather than restating the emptiness body at
    ///   every callsite.
    ///
    /// # Theory grounding
    ///
    /// - THEORY.md §II.1 invariant 5 — composition preserves proofs.
    ///   The zero-endpoint projection on the closed-set-inversion axis
    ///   lives at ONE substrate site as a short-circuiting closed-set
    ///   walk over the load-bearing distinct iterator. Every downstream
    ///   consumer whose semantic reading is "no kind is present" reads
    ///   through this primitive rather than paying for the widened
    ///   primitive's Vec allocation, the scalar counter's full-slot
    ///   walk, or the negation-at-callsite of the at-least-one halfspace
    ///   primitive.
    /// - THEORY.md §VI.1 — generation over composition. A new
    ///   [`ConditionKind`] variant added to `ALL` reaches this primitive
    ///   mechanically through the load-bearing distinct iterator — an
    ///   empty slice (returning `true` here) that later picks up any
    ///   variant flips to `false` at every downstream `is-kind-empty`
    ///   callsite. Byte-for-byte symmetrical with the wider-set
    ///   propagation on `is_kind_saturated` under the (distinct, missing)
    ///   axis-parity.
    fn is_kind_empty(&self) -> bool {
        self.iter_distinct_kinds().next().is_none()
    }

    /// Boolean cardinality parent-state middle-arm peer of
    /// [`Self::is_kind_empty`] and [`Self::is_kind_saturated`] on the
    /// closed-set-partition axis — `true` iff AT LEAST ONE
    /// [`ConditionKind::ALL`] variant appears at least once in this slice
    /// AND AT LEAST ONE [`ConditionKind::ALL`] variant is absent from every
    /// condition (equivalently, `0 < distinct_kind_count < ConditionKind::ALL.len()`
    /// and `0 < missing_kind_count < ConditionKind::ALL.len()`).
    ///
    /// Default body: a FUSED short-circuit closed-set walk over
    /// [`ConditionKind::ALL`] that flips a two-bit `(has_present,
    /// has_missing)` witness on each kind under [`Self::has_kind`] and
    /// returns `true` at the FIRST kind whose flip closes both bits,
    /// WITHOUT materializing [`Self::distinct_kinds`] or
    /// [`Self::missing_kinds`], WITHOUT walking every slot to build
    /// [`Self::distinct_kind_count`] or [`Self::missing_kind_count`],
    /// and WITHOUT allocating a two-Vec negation-of-both-endpoints
    /// composition at the callsite. Byte-for-byte cheaper than the
    /// widened negation composition
    /// `!self.is_kind_empty() && !self.is_kind_saturated()` (which pays
    /// two separate `ALL`-length short-circuit walks on saturated /
    /// empty arms) on every arm where the FIRST and SECOND slot kinds
    /// bracket the closed set on opposite bits — the fused walk exits
    /// on the SECOND slot of `ConditionKind::ALL` whenever the two
    /// pass-side bits close, cheaper than either widened primitive on
    /// the mid-arm sweep.
    ///
    /// # Peer to [`crate::tagged_union::TaggedUnion::is_partially_populated`]
    ///
    /// Slice-level peer of the tagged-union parent-level middle-arm
    /// predicate one struct-layer up: where
    /// [`crate::tagged_union::TaggedUnion::is_partially_populated`]
    /// answers "is SOME slot on the tagged-union parent occupied AND
    /// SOME slot missing?", `is_kind_partially_covered` answers "does
    /// SOME kind appear in AT LEAST ONE condition of the slice AND SOME
    /// kind APPEAR IN NONE?". Both compose against a FUSED
    /// short-circuit closed-set walk under the SAME presence predicate
    /// (`has(kind)` / `has_kind(kind)`) at two adjacent typescape sites
    /// — the two primitives close the parent-state middle-arm on the
    /// closed-set partition at both struct layers under the SAME shape.
    /// The trichotomy partition law
    /// `usize::from(is_kind_empty()) +
    /// usize::from(is_kind_partially_covered()) +
    /// usize::from(is_kind_saturated()) == 1` on any `N ≥ 1` closed
    /// set is pinned as a first-class typed invariant by
    /// [`assert_slice_refinement_composition_laws`] as its parent-state
    /// trichotomy arm, byte-for-byte peer of
    /// [`crate::tagged_union::assert_is_partially_populated_matches_cardinality`]
    /// one struct-layer up.
    ///
    /// # Sibling to [`Self::is_kind_empty`] / [`Self::is_kind_saturated`]
    ///
    /// Third and final arm of the `(empty, partially covered, saturated)`
    /// parent-state trichotomy on the closed-set-partition axis at the
    /// slice level, closing the natural partition alongside
    /// `is_kind_empty` (=0 zero-endpoint on the distinct axis) and
    /// `is_kind_saturated` (=0 zero-endpoint on the missing axis).
    /// Every slice satisfies EXACTLY ONE of the three Boolean
    /// projections on any `N ≥ 1` closed set — the three primitives
    /// partition the (distinct_kind_count, missing_kind_count) product
    /// at (0, N), (open interval, open interval), and (N, 0)
    /// respectively.
    ///
    /// # Composition laws
    ///
    /// - `is_kind_partially_covered() == !is_kind_empty() && !is_kind_saturated()`
    ///   — the negation-of-both-endpoints composition, at the trait
    ///   default body's SAME fused short-circuit walk.
    /// - `is_kind_partially_covered() == has_any_distinct_kind() && has_any_missing_kind()`
    ///   — the paired at-least-one-halfspace composition binding this
    ///   Boolean projection to the at-least-one halfspace peers on both
    ///   axes.
    /// - `is_kind_partially_covered() == (distinct_kind_count() > 0 && missing_kind_count() > 0)`
    ///   — the paired scalar-projection composition binding this
    ///   Boolean projection to the widened + scalar peers on both axes.
    ///
    /// # Semantics
    ///
    /// An empty slice returns `false` (0 distinct + N missing hits the
    /// `is_kind_empty` arm, not the middle arm). A slice carrying a
    /// strict subset of [`ConditionKind::ALL`] returns `true` on any
    /// `N ≥ 2` closed set (some kind present, some absent). A saturated
    /// slice returns `false` (N distinct + 0 missing hits the
    /// `is_kind_saturated` arm, not the middle arm). Multiplicity is
    /// irrelevant on both sides — the predicate collapses to
    /// non-emptiness of both the distinct SET and the missing SET.
    ///
    /// # Compounding future consumers
    ///
    /// - A boundary-progress "some kinds covered, some pending"
    ///   diagnostic on a Boundary slice reads
    ///   `boundary.postconditions.is_kind_partially_covered()` at ONE
    ///   substrate site — the exact "in-flight coverage" arm — rather
    ///   than composing
    ///   `!boundary.postconditions.is_kind_empty() && !boundary.postconditions.is_kind_saturated()`
    ///   (two closed-set walks) or
    ///   `boundary.postconditions.distinct_kind_count() > 0 && boundary.postconditions.missing_kind_count() > 0`
    ///   (two counter walks with no short-circuit).
    /// - A fleet-wide "mixed coverage" fast-path that discriminates
    ///   "partial" from "empty or saturated" reads this primitive with
    ///   ONE fused short-circuit walk, strictly cheaper than either
    ///   widened composition.
    /// - An `is-kind-partially-covered` require-tag classifier arm
    ///   reaches this primitive at ONE call site, byte-for-byte
    ///   symmetrical with the sibling `is-kind-empty` /
    ///   `is-kind-saturated` arms on the closed parent-state trichotomy.
    ///
    /// # Theory grounding
    ///
    /// - THEORY.md §II.1 invariant 5 — composition preserves proofs.
    ///   The parent-state middle-arm projection on the closed-set
    ///   partition lives at ONE substrate site as a FUSED short-circuit
    ///   walk over `ConditionKind::ALL` under [`Self::has_kind`] with
    ///   early exit on the first observed present/missing pair —
    ///   byte-for-byte cheaper than the widened negation-of-both-
    ///   endpoints composition, and semantically identical on every
    ///   arm. The trichotomy partition law
    ///   `is_kind_empty + is_kind_partially_covered + is_kind_saturated == 1`
    ///   lives at ONE substrate site inside the composition-law
    ///   testkit's per-arm sweep — pinned across every production
    ///   slice at compile time via the trait's default body
    ///   composition, not per-slice.
    /// - THEORY.md §VI.1 — generation over composition. A new
    ///   [`ConditionKind`] variant added to `ALL` reaches this primitive
    ///   mechanically through the fused walk — the trichotomy holds
    ///   on the widened kind set without further per-caller edit
    ///   (a slice previously at the middle arm continues to satisfy
    ///   it if it does not add the new variant; a previously-saturated
    ///   slice that leaves the new variant missing becomes partially
    ///   covered at every downstream callsite).
    fn is_kind_partially_covered(&self) -> bool {
        let mut has_present = false;
        let mut has_missing = false;
        for k in ConditionKind::ALL {
            if self.has_kind(k) {
                has_present = true;
            } else {
                has_missing = true;
            }
            if has_present && has_missing {
                return true;
            }
        }
        false
    }

    /// Boolean at-least-one halfspace peer of [`Self::has_any_missing_kind`]
    /// on the closed-set-inversion axis — `true` iff AT LEAST ONE
    /// [`ConditionKind::ALL`] variant appears at least once in this slice
    /// (equivalently, [`Self::distinct_kinds`] is non-empty,
    /// [`Self::distinct_kind_count`] `> 0`, and
    /// [`Self::first_distinct_kind`] is `Some`).
    ///
    /// Default body: `ConditionKind::ALL.iter().copied().any(|k|
    /// self.has_kind(k))` — a SHORT-CIRCUITING closed-set walk that
    /// returns `true` at the FIRST populated kind WITHOUT materializing
    /// [`Self::distinct_kinds`]'s `Vec`, WITHOUT walking every slot to
    /// build [`Self::distinct_kind_count`]'s scalar, and WITHOUT
    /// allocating the closed-set-inversion scan. Strictly cheaper than
    /// either widened primitive on every non-empty arm because the walk
    /// short-circuits at the first `has_kind` hit rather than paying
    /// for the Vec allocation or the full cardinality count.
    ///
    /// # Peer to [`crate::tagged_union::TaggedUnion::has_any_populated_kind`]
    ///
    /// Slice-level peer of the tagged-union parent-level at-least-one
    /// halfspace predicate one struct-layer up: where
    /// [`crate::tagged_union::TaggedUnion::has_any_populated_kind`]
    /// answers "is ANY slot on the tagged-union parent occupied?",
    /// `has_any_distinct_kind` answers "does ANY kind appear in AT
    /// LEAST ONE condition of the slice?". Both compose against a
    /// SHORT-CIRCUITING closed-set walk under the SAME `has` /
    /// `has_kind` predicate at two adjacent typescape sites — the two
    /// primitives close the at-least-one halfspace on the closed-set-
    /// inversion axis at both struct layers under the SAME shape.
    ///
    /// # Sibling to [`Self::has_any_missing_kind`]
    ///
    /// Closed-set-inversion peer of the at-least-one halfspace on the
    /// closed-set-complement axis — where `has_any_missing_kind`
    /// returns `true` iff at least one kind is ABSENT,
    /// `has_any_distinct_kind` returns `true` iff at least one kind is
    /// PRESENT. Together with their zero-arm endpoints
    /// ([`Self::is_kind_saturated`] on the missing axis and the empty-
    /// slice endpoint on the distinct axis), the two Booleans partition
    /// the (distinct, missing) product: a slice is EMPTY iff neither
    /// `has_any_distinct_kind()` nor `is_kind_saturated()` returns
    /// `true`; a slice is SATURATED iff both `has_any_distinct_kind()`
    /// returns `true` and `has_any_missing_kind()` returns `false`; a
    /// slice is PARTIALLY POPULATED iff both `has_any_distinct_kind()`
    /// and `has_any_missing_kind()` return `true`.
    ///
    /// # Sibling to [`Self::distinct_kinds`] / [`Self::distinct_kind_count`]
    ///
    /// Boolean at-least-one halfspace peer of the widened + scalar
    /// closed-set-inversion primitives — where `distinct_kinds` returns
    /// the FULL distinct SET and `distinct_kind_count` returns its
    /// cardinality, `has_any_distinct_kind` collapses either the
    /// widened primitive to its non-emptiness Boolean or the scalar to
    /// its `>= 1` halfspace Boolean. The composition laws
    /// `has_any_distinct_kind() == !distinct_kinds().is_empty()` and
    /// `has_any_distinct_kind() == (distinct_kind_count() > 0)` bind
    /// this Boolean projection to the widened + scalar primitives at
    /// the trait's default body — strictly cheaper than either widened
    /// primitive on every non-empty arm because the walk short-circuits
    /// at the first populated kind on the has-side walk rather than
    /// allocating the closed-set-inversion scan or walking every slot
    /// to build the scalar cardinality.
    ///
    /// # Semantics
    ///
    /// An empty slice returns `false` — the SOLE arm on which
    /// `has_any_distinct_kind` returns `false`. A slice carrying any
    /// [`ConditionKind`] at least once returns `true` (a single-
    /// populated slice, a partially-populated slice, and a saturated
    /// slice all return `true`).
    ///
    /// # Compounding future consumers
    ///
    /// - A fleet-wide "any coverage at all" fast-path that discriminates
    ///   "the slice carries at least one closed-set kind" from "the
    ///   slice is empty" reads
    ///   `boundary.postconditions.has_any_distinct_kind()` at ONE call
    ///   site rather than restating `distinct_kind_count() > 0` (which
    ///   walks every slot to count) or `!distinct_kinds().is_empty()`
    ///   (which allocates the Vec before the negated emptiness check).
    /// - A `has-any-distinct-kind` require-tag classifier arm reaches
    ///   this primitive with no allocation, byte-for-byte peer of the
    ///   tagged-union `has-any-populated-kind` classifier one struct-
    ///   layer up under the SAME `any(has)` short-circuit shape.
    /// - A coherence check that flags "any process boundary whose
    ///   postcondition slice covers at least one [`ConditionKind`]"
    ///   reads `boundary.postconditions.has_any_distinct_kind()` at
    ///   ONE substrate primitive per test rather than restating the
    ///   `.iter().copied().any(|k| slice.has_kind(k))` body at every
    ///   callsite.
    ///
    /// # Theory grounding
    ///
    /// - THEORY.md §II.1 invariant 5 — composition preserves proofs.
    ///   The at-least-one halfspace projection on the closed-set-
    ///   inversion axis lives at ONE substrate site as a typed short-
    ///   circuiting closed-set walk `ConditionKind::ALL.iter().any(
    ///   has_kind)`. Every downstream consumer whose semantic reading
    ///   is "at least one kind is present" reads through this
    ///   primitive rather than paying for the widened primitive's Vec
    ///   allocation.
    /// - THEORY.md §VI.1 — generation over composition. A new
    ///   [`ConditionKind`] variant added to `ALL` reaches this
    ///   primitive mechanically through the `any` short-circuit — an
    ///   empty slice (returning `false` here) that later picks up the
    ///   new variant returns `true` at every downstream `has-any-
    ///   distinct-kind` callsite.
    fn has_any_distinct_kind(&self) -> bool {
        self.iter_distinct_kinds().next().is_some()
    }

    /// Boolean cardinality-mid-endpoint peer of
    /// [`Self::has_any_distinct_kind`] on the closed-set-inversion
    /// axis — `true` iff EXACTLY ONE [`ConditionKind::ALL`] variant
    /// appears at least once in this slice (equivalently,
    /// [`Self::distinct_kind_count`] `== 1`,
    /// [`Self::distinct_kinds`]`.len() == 1`, and
    /// [`Self::first_distinct_kind`] equals
    /// [`Self::last_distinct_kind`] and is [`Some`]).
    ///
    /// Default body: a two-step-short-circuit closed-set walk over
    /// [`Self::iter_distinct_kinds`] — pulls up to two hits off the
    /// load-bearing distinct iterator; the primitive returns `true`
    /// iff the first hit is [`Some`] and the second is [`None`],
    /// WITHOUT materializing [`Self::distinct_kinds`]'s `Vec` and
    /// WITHOUT walking every slot to build
    /// [`Self::distinct_kind_count`]'s scalar. Short-circuits at the
    /// second distinct kind — strictly cheaper than either widened
    /// primitive on every arm with `≥ 2` distinct kinds.
    ///
    /// # Peer to [`crate::tagged_union::TaggedUnion::has_unique_populated_kind`]
    ///
    /// Slice-level peer of the tagged-union parent-level
    /// cardinality-mid-endpoint predicate one struct-layer up: where
    /// [`crate::tagged_union::TaggedUnion::has_unique_populated_kind`]
    /// answers "is EXACTLY ONE slot on the tagged-union parent
    /// occupied?", `has_unique_distinct_kind` answers "does EXACTLY
    /// ONE kind appear in AT LEAST ONE condition of the slice?". Both
    /// compose against a two-step-short-circuit walk under the SAME
    /// presence predicate (`has(kind)` / `has_kind(kind)`) at two
    /// adjacent typescape sites — the two primitives close the
    /// exactly-one-arm on the closed-set-inversion axis at both
    /// struct layers under the SAME shape.
    ///
    /// # Sibling to [`Self::has_unique_missing_kind`]
    ///
    /// Closed-set-inversion peer of the cardinality-mid-endpoint on
    /// the closed-set-complement axis — where
    /// `has_unique_missing_kind` returns `true` iff exactly one kind
    /// is ABSENT (the near-saturation-endpoint arm),
    /// `has_unique_distinct_kind` returns `true` iff exactly one kind
    /// is PRESENT (the singleton-coverage arm). Both close the
    /// exactly-one arm on their respective axis under the SAME
    /// two-step short-circuit walk shape via the load-bearing
    /// iterator peer.
    ///
    /// # Semantics
    ///
    /// An empty slice returns `false` (0 distinct, not 1). A slice
    /// carrying a single [`ConditionKind`] (with any multiplicity)
    /// returns `true` — the SOLE arm where
    /// `has_unique_distinct_kind` returns `true` on any `N ≥ 2`
    /// closed set. A slice carrying `K ≥ 2` distinct kinds returns
    /// `false`. A saturated slice returns `false` on `N ≥ 2` closed
    /// sets (every kind present, not exactly 1).
    ///
    /// # Compounding future consumers
    ///
    /// - A fleet-wide "singleton coverage" fast-path that
    ///   discriminates "the slice carries exactly one ALL variant"
    ///   from every other cardinality reads
    ///   `boundary.postconditions.has_unique_distinct_kind()` at ONE
    ///   call site — one two-step short-circuit walk, no allocation,
    ///   no scalar equality against `1`, byte-for-byte peer of the
    ///   tagged-union `has-unique-populated-kind` classifier one
    ///   struct-layer up under the SAME two-step short-circuit shape.
    /// - A `has-unique-distinct-kind` require-tag classifier arm
    ///   reaches this primitive with no allocation.
    /// - A future singleton-coverage diagnostic that prints "the SOLE
    ///   [`ConditionKind`] covered by this Boundary" pairs
    ///   `has_unique_distinct_kind()` with
    ///   [`Self::first_distinct_kind`] to name the SOLE distinct kind
    ///   without allocating [`Self::distinct_kinds`]'s `Vec`.
    ///
    /// # Theory grounding
    ///
    /// - THEORY.md §II.1 invariant 5 — composition preserves proofs.
    ///   The cardinality-mid-endpoint projection on the closed-set-
    ///   inversion axis lives at ONE substrate site as a typed
    ///   two-step-short-circuit fold through the load-bearing
    ///   [`Self::iter_distinct_kinds`] iterator — byte-for-byte peer
    ///   of `distinct_kind_count()` composed against `== 1`, but with
    ///   a second-distinct-slot short-circuit that the scalar counter
    ///   primitive does not offer.
    /// - THEORY.md §VI.1 — generation over composition. A new
    ///   [`ConditionKind`] variant added to `ALL` reaches this
    ///   primitive mechanically through the short-circuit walk — a
    ///   slice previously at the singleton-coverage arm (returned
    ///   `true` here) that also picks up the new variant now has
    ///   TWO distinct kinds and returns `false`.
    fn has_unique_distinct_kind(&self) -> bool {
        let mut it = self.iter_distinct_kinds();
        it.next().is_some() && it.next().is_none()
    }

    /// Witnessing `Option<ConditionKind>` peer of
    /// [`Self::has_unique_distinct_kind`] on the closed-set-inversion
    /// axis — `Some(k)` iff `k` is the SOLE [`ConditionKind::ALL`]
    /// variant appearing at least once in this slice, else `None`.
    ///
    /// Default body: a two-step-short-circuit fold through
    /// [`Self::iter_distinct_kinds`] — pull the first hit; return
    /// `Some(first)` iff the second hit is [`None`], else `None`.
    /// Byte-for-byte peer of
    /// [`crate::tagged_union::TaggedUnion::unique_populated_kind`]
    /// one struct-layer up under the SAME `iter_populated_kinds`
    /// two-step short-circuit shape, and the WITNESSING scalar peer of
    /// the Boolean [`Self::has_unique_distinct_kind`] predicate at the
    /// SAME two-step short-circuit shape.
    ///
    /// # Sibling to [`Self::first_distinct_kind`] / [`Self::last_distinct_kind`]
    ///
    /// FIFTH refinement on the closed-set-inversion axis under exactly-
    /// one-hit semantics, `Option<ConditionKind>`-valued: together with
    /// [`Self::first_distinct_kind`] and [`Self::last_distinct_kind`]
    /// the three primitives project [`Self::distinct_kinds`] onto its
    /// cardinality-conditioned scalar identity on the present side. The
    /// composition laws
    /// `unique_distinct_kind().is_some() == (distinct_kind_count() == 1)`
    /// and (on the `Some` arm) `unique_distinct_kind() ==
    /// first_distinct_kind() == last_distinct_kind()` bind the exactly-
    /// one scalar identity to the widened primitives at the trait's
    /// default body.
    ///
    /// # Peer to [`Self::unique_missing_kind`]
    ///
    /// Closed-set-inversion peer of the exactly-one-hit scalar on the
    /// closed-set-complement axis — where `unique_missing_kind` names
    /// the SOLE ABSENT kind, `unique_distinct_kind` names the SOLE
    /// PRESENT kind. The two primitives close the (present, absent) x
    /// (endpoint, exactly-one) 2x3 scalar-Option grid on the slice
    /// level under the SAME two-step short-circuit shape via the
    /// load-bearing iterator peers.
    ///
    /// # Semantics
    ///
    /// An empty slice returns `None` (0 distinct, not 1). A slice
    /// carrying a single [`ConditionKind`] (with any multiplicity)
    /// returns `Some(k)` — the SOLE arm where `unique_distinct_kind`
    /// returns `Some` on any `N ≥ 2` closed set. A slice carrying `K ≥ 2`
    /// distinct kinds returns `None`. A saturated slice returns `None`
    /// on `N ≥ 2` closed sets.
    ///
    /// # Compounding future consumers
    ///
    /// - A future singleton-coverage diagnostic that prints "the SOLE
    ///   [`ConditionKind`] covered by this Boundary is X" reads
    ///   `boundary.postconditions.unique_distinct_kind()` at ONE call
    ///   site — the WITNESS + the exactly-one predicate composed at
    ///   ONE short-circuit walk, rather than pairing the Boolean
    ///   [`Self::has_unique_distinct_kind`] with [`Self::first_distinct_kind`]
    ///   at TWO independent walks whose agreement is a coincidence.
    /// - A `unique-distinct-<kind>` require-tag classifier arm reads
    ///   this primitive with no allocation, byte-for-byte symmetrical
    ///   with `slice.unique_missing_kind()`.
    /// - A fast-path branch that discriminates "exactly one kind
    ///   covered" from "0 or ≥ 2 covered" reads
    ///   `slice.unique_distinct_kind().is_some()` at ONE call site.
    ///
    /// # Theory grounding
    ///
    /// - THEORY.md §II.1 invariant 5 — composition preserves proofs.
    ///   The exactly-one-hit witnessing projection on the closed-set-
    ///   inversion axis lives at ONE substrate site as a typed two-
    ///   step-short-circuit fold through the load-bearing
    ///   [`Self::iter_distinct_kinds`] iterator — byte-for-byte peer of
    ///   the tagged-union [`crate::tagged_union::TaggedUnion::unique_populated_kind`]
    ///   under the SAME iterator shape.
    /// - THEORY.md §VI.1 — generation over composition. A new
    ///   [`ConditionKind`] variant added to `ALL` reaches this
    ///   primitive mechanically through the short-circuit walk — a
    ///   slice previously at the singleton-coverage arm (returned
    ///   `Some(k)` here) that also picks up the new variant now has
    ///   TWO distinct kinds and returns `None`.
    fn unique_distinct_kind(&self) -> Option<ConditionKind> {
        let mut it = self.iter_distinct_kinds();
        let first = it.next()?;
        match it.next() {
            None => Some(first),
            Some(_) => None,
        }
    }

    /// Boolean cardinality many-arm peer of
    /// [`Self::has_unique_distinct_kind`] on the closed-set-inversion
    /// axis — `true` iff AT LEAST TWO [`ConditionKind::ALL`] variants
    /// appear at least once in this slice (equivalently,
    /// [`Self::distinct_kind_count`] `>= 2` and
    /// [`Self::distinct_kinds`]`.len() >= 2`).
    ///
    /// Default body: a two-step-short-circuit closed-set walk over
    /// [`Self::iter_distinct_kinds`] — pulls up to two hits off the
    /// load-bearing distinct iterator; the primitive returns `true`
    /// iff BOTH the first and the second are [`Some`], WITHOUT
    /// materializing [`Self::distinct_kinds`]'s `Vec` and WITHOUT
    /// walking every slot to build [`Self::distinct_kind_count`]'s
    /// scalar. Short-circuits at the second distinct kind — strictly
    /// cheaper than either widened primitive on every arm with `≥ 2`
    /// distinct kinds. Byte-for-byte peer of
    /// [`crate::tagged_union::TaggedUnion::has_multiple_populated_kinds`]
    /// under the (populated, missing) inversion axis one struct-layer
    /// up.
    ///
    /// # Peer to [`crate::tagged_union::TaggedUnion::has_multiple_populated_kinds`]
    ///
    /// Slice-level peer of the tagged-union parent-level cardinality
    /// many-arm predicate one struct-layer up: where
    /// [`crate::tagged_union::TaggedUnion::has_multiple_populated_kinds`]
    /// answers "are AT LEAST TWO slots on the tagged-union parent
    /// occupied?", `has_multiple_distinct_kinds` answers "do AT LEAST
    /// TWO kinds appear in AT LEAST ONE condition of the slice?". Both
    /// compose against a two-step-short-circuit closed-set walk under
    /// a presence predicate (`has(kind)` / `has_kind(kind)`) at two
    /// adjacent typescape sites — the two primitives close the at-
    /// least-two arm on the closed-set-inversion axis at both struct
    /// layers under the SAME shape.
    ///
    /// # Sibling to the Boolean distinct-cardinality trichotomy
    ///
    /// Third and final arm of the `{0, 1, ≥2}` cardinality trichotomy
    /// on the distinct axis at the slice level, closing the natural
    /// partition alongside the zero-arm (the empty-distinct endpoint,
    /// reached via `!has_any_distinct_kind()`) and
    /// [`Self::has_unique_distinct_kind`] (one-arm). Every slice
    /// satisfies EXACTLY ONE of the three Boolean projections — the
    /// three primitives partition `0..=ConditionKind::ALL.len()` at 0,
    /// 1, and ≥ 2 respectively. The composition law
    /// `has_multiple_distinct_kinds() == (distinct_kind_count() >= 2)`
    /// binds the Boolean projection to the scalar primitive at the
    /// trait's default body — swept substrate-wide by
    /// [`assert_slice_refinement_composition_laws`] as its
    /// distinct-cardinality-many-arm arm.
    ///
    /// # Semantics
    ///
    /// An empty slice returns `false` (0 distinct, not ≥ 2). A slice
    /// carrying a single [`ConditionKind`] (with any multiplicity)
    /// returns `false` (1 distinct, not ≥ 2). A slice carrying `K ≥ 2`
    /// distinct kinds returns `true`. A saturated slice returns `true`
    /// on any `N ≥ 2` closed set (every kind present, ≥ 2 ≥ 2).
    ///
    /// # Compounding future consumers
    ///
    /// - An operator-facing "≥ 2 dependencies covered" fast-path
    ///   discriminator on the many-distinct arm reads
    ///   `boundary.postconditions.has_multiple_distinct_kinds()` at
    ///   ONE call site — one two-step short-circuit walk, no
    ///   allocation, no scalar comparison against `>= 2`, byte-for-
    ///   byte peer of the tagged-union `has-multiple-populated-kinds`
    ///   classifier one struct-layer up under the SAME two-step
    ///   short-circuit shape.
    /// - A `has-multiple-distinct-kinds` require-tag classifier arm
    ///   reaches this primitive with no allocation, byte-for-byte
    ///   peer of the tagged-union `has-multiple-populated-kinds`
    ///   classifier one struct-layer up.
    /// - A future multi-coverage diagnostic that prints "≥ 2 distinct
    ///   ConditionKinds covered by this Boundary" reads
    ///   `has_multiple_distinct_kinds()` at ONE call site without
    ///   allocating [`Self::distinct_kinds`]'s `Vec`.
    ///
    /// # Theory grounding
    ///
    /// - THEORY.md §II.1 invariant 5 — composition preserves proofs.
    ///   The cardinality-many-arm projection on the distinct axis
    ///   lives at ONE substrate site as a typed two-step-short-circuit
    ///   fold through the load-bearing [`Self::iter_distinct_kinds`]
    ///   iterator — byte-for-byte peer of `distinct_kind_count()`
    ///   composed against `>= 2`, but with a second-distinct-slot
    ///   short-circuit that the scalar counter primitive does not
    ///   offer.
    /// - THEORY.md §VI.1 — generation over composition. A new
    ///   [`ConditionKind`] variant added to `ALL` reaches this
    ///   primitive mechanically through the short-circuit walk — a
    ///   slice previously at the singleton-coverage arm (returned
    ///   `false` here) that also picks up the new variant now has TWO
    ///   distinct kinds and flips to `true`.
    fn has_multiple_distinct_kinds(&self) -> bool {
        let mut it = self.iter_distinct_kinds();
        it.next().is_some() && it.next().is_some()
    }

    /// Boolean cardinality "≤ 1" negation peer of
    /// [`Self::has_multiple_distinct_kinds`] on the closed-set-inversion
    /// axis — `true` iff AT MOST ONE [`ConditionKind::ALL`] variant
    /// appears at least once in this slice (equivalently,
    /// [`Self::distinct_kind_count`] `<= 1` and
    /// [`Self::distinct_kinds`]`.len() <= 1`). Closes the {0, 1, ≥2, ≤1}
    /// Boolean-negation grid on the distinct axis at the slice level
    /// alongside its sibling `has_multiple_distinct_kinds` (≥ 2 many-
    /// arm) under the definitional negation `!(≥ 2) == (≤ 1)`, and
    /// alongside `!has_any_distinct_kind` (=0 empty-endpoint) OR
    /// `has_unique_distinct_kind` (=1 mid-endpoint) as the trichotomy-
    /// union arm. Names the arrangement space where the slice is
    /// EMPTY-OR-SINGLETON (zero or exactly one distinct kind).
    ///
    /// Default body: `!self.has_multiple_distinct_kinds()` — a
    /// definitional Boolean negation of the many-arm primitive. Short-
    /// circuits transitively through
    /// [`Self::has_multiple_distinct_kinds`]'s two-step short-circuit
    /// walk over [`Self::iter_distinct_kinds`]: returns `true` as soon
    /// as the many-arm walk stops with fewer than two distinct hits,
    /// WITHOUT materializing [`Self::distinct_kinds`]'s `Vec` and
    /// WITHOUT walking every slot to build
    /// [`Self::distinct_kind_count`]'s scalar. Byte-for-byte peer of
    /// [`crate::tagged_union::TaggedUnion::has_at_most_one_populated_kind`]
    /// under the (populated, missing) inversion axis one struct-layer
    /// up, both composed as the same definitional negation of their
    /// respective many-arm primitives.
    ///
    /// # Peer to [`crate::tagged_union::TaggedUnion::has_at_most_one_populated_kind`]
    ///
    /// Slice-level peer of the tagged-union parent-level cardinality
    /// "≤ 1" predicate one struct-layer up: where
    /// [`crate::tagged_union::TaggedUnion::has_at_most_one_populated_kind`]
    /// answers "does the tagged-union parent have AT MOST ONE occupied
    /// slot?", `has_at_most_one_distinct_kind` answers "do AT MOST ONE
    /// kind appear in AT LEAST ONE condition of the slice?". Both
    /// compose as the definitional Boolean negation of their many-arm
    /// primitive (`!has_multiple_populated_kinds()` /
    /// `!has_multiple_distinct_kinds()`) at two adjacent typescape
    /// sites — the two primitives close the "≤ 1" arm on the closed-
    /// set-inversion axis at both struct layers under the SAME shape.
    ///
    /// # Peer to [`Self::has_at_most_one_missing_kind`]
    ///
    /// Axis-parity mirror of the closed-set-complement "≤ 1" negation
    /// peer at the slice level — where `has_at_most_one_missing_kind`
    /// tests "at most one kind MISSING" (near-saturation-or-saturated),
    /// `has_at_most_one_distinct_kind` tests "at most one kind
    /// PRESENT" (empty-or-singleton). Both compose the same
    /// definitional negation shape (`!has_multiple_*_kinds()`) at the
    /// slice-level trait's default body — the two primitives close the
    /// "≤ 1" arm on both the closed-set-complement and closed-set-
    /// inversion axes at the SAME struct layer under the SAME shape.
    ///
    /// # Sibling to the Boolean distinct-cardinality tetrachotomy
    ///
    /// Fourth arm of the `{0, ≥1, 1, ≥2, ≤1}` Boolean-cardinality
    /// closure on the distinct axis at the slice level, closing the
    /// Boolean-negation grid alongside `!has_any_distinct_kind` (=0
    /// zero-arm reached via [`Self::has_any_distinct_kind`]),
    /// [`Self::has_unique_distinct_kind`] (=1 mid-endpoint),
    /// [`Self::has_any_distinct_kind`] (≥1 halfspace), and
    /// [`Self::has_multiple_distinct_kinds`] (≥2 many-arm). The
    /// {≤1, ≥2} pair sit on the Boolean-negation axis:
    /// `has_at_most_one_distinct_kind == !has_multiple_distinct_kinds`
    /// on every arm. The {0, 1} union arm sits on the trichotomy-union
    /// axis: `has_at_most_one_distinct_kind == !has_any_distinct_kind
    /// || has_unique_distinct_kind` on every arm. Both composition laws
    /// bind the "≤ 1" Boolean projection to the sibling primitives at
    /// the trait's default body — swept substrate-wide by
    /// [`assert_slice_refinement_composition_laws`] as its distinct-
    /// axis "≤ 1" arm.
    ///
    /// # Semantics
    ///
    /// An empty slice returns `true` (0 distinct, `≤ 1`) — the dual of
    /// the empty-slice arm on [`Self::has_at_most_one_missing_kind`]
    /// which returns `false` on `N ≥ 2` closed sets (empty means every
    /// kind missing, `N ≥ 2` missing, not `≤ 1`). A slice carrying a
    /// single [`ConditionKind`] (with any multiplicity) returns `true`
    /// (1 distinct, `≤ 1`) — the singleton arm on the distinct axis.
    /// A slice carrying `K ≥ 2` distinct kinds returns `false`. A
    /// saturated slice returns `false` on any `N ≥ 2` closed set
    /// (every kind present, `N ≥ 2` distinct, not `≤ 1`) — the union of
    /// the two "≤ 1" arms (`=0` and `=1`) is exactly the arrangement
    /// space where the primitive returns `true`.
    ///
    /// # Compounding future consumers
    ///
    /// - An operator-facing "at most one dependency currently covered"
    ///   fast-path discriminator on the empty / singleton-coverage arms
    ///   reads `boundary.postconditions.has_at_most_one_distinct_kind()`
    ///   at ONE call site — one bit-flip on the many-arm's two-step
    ///   short-circuit walk, no allocation, no scalar comparison
    ///   against `<= 1`, byte-for-byte peer of the tagged-union
    ///   `has-at-most-one-populated-kind` classifier one struct-layer
    ///   up under the SAME `!has_multiple_populated_kinds` definitional
    ///   negation shape.
    /// - A `has-at-most-one-distinct-kind` require-tag classifier arm
    ///   reaches this primitive with no allocation, closing the
    ///   {0, 1, ≥ 2, ≤ 1} cardinality-Boolean grid on the distinct axis
    ///   at the slice level alongside its sibling
    ///   `has-multiple-distinct-kinds` under the Boolean negation axis
    ///   and the missing-axis peer `has-at-most-one-missing-kind` under
    ///   the closed-set-inversion axis.
    /// - A future under-coverage diagnostic that says "at most one
    ///   ConditionKind covered by this Boundary" reads
    ///   `has_at_most_one_distinct_kind()` at ONE call site without
    ///   allocating [`Self::distinct_kinds`]'s `Vec`.
    ///
    /// # Theory grounding
    ///
    /// - THEORY.md §II.1 invariant 5 — composition preserves proofs.
    ///   The cardinality "≤ 1" projection on the distinct axis lives
    ///   at ONE substrate site as the definitional Boolean negation
    ///   of [`Self::has_multiple_distinct_kinds`]; the three composition
    ///   forms (`!has_multiple_distinct_kinds()`,
    ///   `distinct_kind_count() <= 1`, and `!has_any_distinct_kind() ||
    ///   has_unique_distinct_kind()`) compose through the SAME two-
    ///   step-short-circuit walk shape one negation up, byte-for-byte
    ///   identical on every arm.
    /// - THEORY.md §VI.1 — generation over composition. A new
    ///   [`ConditionKind`] variant added to `ALL` reaches this
    ///   primitive mechanically through the delegated
    ///   [`Self::has_multiple_distinct_kinds`] — a slice previously at
    ///   the singleton arm (returned `true` here) that also picks up
    ///   the new variant now has TWO distinct kinds and flips to
    ///   `false`.
    fn has_at_most_one_distinct_kind(&self) -> bool {
        !self.has_multiple_distinct_kinds()
    }

    /// Boolean at-least-one halfspace peer of [`Self::is_kind_saturated`]
    /// on the closed-set-complement axis — `true` iff AT LEAST ONE
    /// [`ConditionKind::ALL`] variant appears zero times in this slice
    /// (equivalently, [`Self::missing_kinds`] is non-empty,
    /// [`Self::missing_kind_count`] `> 0`, [`Self::first_missing_kind`]
    /// is `Some`).
    ///
    /// Default body: `!self.is_kind_saturated()` — a definitional
    /// negation of the saturation-endpoint primitive. Short-circuits
    /// transitively through [`Self::is_kind_saturated`]'s
    /// `ConditionKind::ALL.iter().all(has_kind)` composition: the
    /// underlying `all` walk returns `false` at the FIRST missing kind
    /// (yielding `true` here) WITHOUT materializing
    /// [`Self::missing_kinds`]'s `Vec`, WITHOUT walking every slot to
    /// build [`Self::missing_kind_count`]'s scalar, and WITHOUT
    /// allocating the closed-set-complement scan. Strictly cheaper
    /// than either widened primitive on every partially-populated arm.
    ///
    /// # Peer to [`crate::tagged_union::TaggedUnion::has_any_missing_kind`]
    ///
    /// Slice-level peer of the tagged-union parent-level at-least-one
    /// halfspace predicate one struct-layer up: where
    /// [`crate::tagged_union::TaggedUnion::has_any_missing_kind`]
    /// answers "is ANY slot on the tagged-union parent empty?",
    /// `has_any_missing_kind` answers "does ANY kind appear in NO
    /// condition of the slice?". Both compose against their
    /// saturation-endpoint primitive under a definitional negation
    /// (`!is_saturated` / `!is_kind_saturated`) at two adjacent
    /// typescape sites — the two primitives close the at-least-one
    /// halfspace on the closed-set-complement axis at both struct
    /// layers under the SAME shape.
    ///
    /// # Sibling to [`Self::is_kind_saturated`]
    ///
    /// Boolean at-least-one halfspace peer of the zero-arm saturation-
    /// endpoint primitive on the closed-set-complement axis — where
    /// `is_kind_saturated` returns `true` iff `missing_kind_count == 0`,
    /// `has_any_missing_kind` returns its Boolean-negation: `true` iff
    /// `missing_kind_count >= 1`. Together the two Booleans partition
    /// the missing-cardinality closed set: exactly one of
    /// `is_kind_saturated()` and `has_any_missing_kind()` is `true`
    /// for every slice. The definitional negation law
    /// `has_any_missing_kind() == !is_kind_saturated()` is pinned as a
    /// first-class typed invariant by the trait's own default body and
    /// swept substrate-wide by
    /// [`assert_slice_refinement_composition_laws`] as its at-least-
    /// one halfspace arm.
    ///
    /// # Sibling to [`Self::missing_kinds`] / [`Self::missing_kind_count`]
    ///
    /// Boolean at-least-one halfspace peer of the widened + scalar
    /// closed-set-complement primitives — where `missing_kinds` returns
    /// the FULL missing SET (a `Vec<ConditionKind>` of every absent
    /// kind) and `missing_kind_count` returns its cardinality
    /// (a `usize` in `0..=ConditionKind::ALL.len()`),
    /// `has_any_missing_kind` collapses either the widened primitive
    /// to its non-emptiness Boolean or the scalar to its `>= 1`
    /// halfspace Boolean. The composition laws
    /// `has_any_missing_kind() == !missing_kinds().is_empty()` and
    /// `has_any_missing_kind() == (missing_kind_count() > 0)` bind
    /// this Boolean projection to the widened + scalar primitives at
    /// the trait's default body — strictly cheaper than either widened
    /// primitive on every partially-populated arm because the negation
    /// short-circuits at the first missing kind on the has-side walk
    /// rather than allocating the closed-set-complement scan or
    /// walking every slot to build the scalar cardinality.
    ///
    /// # Semantics
    ///
    /// An empty slice returns `true` (every kind is missing — the
    /// fully-missing endpoint). A slice carrying a strict subset of
    /// [`ConditionKind::ALL`] returns `true`. A saturated slice
    /// returns `false` — the SOLE arm on which `has_any_missing_kind`
    /// returns `false`, byte-for-byte peer of the SOLE arm on which
    /// `is_kind_saturated` returns `true`.
    ///
    /// # Compounding future consumers
    ///
    /// - A fleet-wide "gap present" fast-path that discriminates "some
    ///   kind is missing" from "every kind is present" reads
    ///   `boundary.postconditions.has_any_missing_kind()` at ONE call
    ///   site rather than negating `is_kind_saturated()` at the
    ///   callsite or restating `missing_kind_count() > 0` (which walks
    ///   every slot to count) or `!missing_kinds().is_empty()` (which
    ///   allocates the Vec before the negated emptiness check).
    /// - A `has-any-missing-kind` require-tag classifier arm reaches
    ///   this primitive with no allocation, byte-for-byte peer of the
    ///   tagged-union `has-any-missing-kind` classifier one struct-
    ///   layer up under the SAME `!is_saturated` definitional negation
    ///   shape.
    /// - A coherence check that flags "any process boundary with a
    ///   missing [`ConditionKind`]" reads
    ///   `boundary.postconditions.has_any_missing_kind()` at ONE
    ///   substrate primitive per test rather than restating the
    ///   negation body at every callsite.
    ///
    /// # Theory grounding
    ///
    /// - THEORY.md §II.1 invariant 5 — composition preserves proofs.
    ///   The at-least-one halfspace projection lives at ONE substrate
    ///   site as a definitional negation of
    ///   [`Self::is_kind_saturated`]. Every downstream consumer whose
    ///   semantic reading is "at least one kind is absent" reads
    ///   through this primitive rather than negating `is_kind_saturated`
    ///   at every callsite or paying for the widened primitive's Vec
    ///   allocation.
    /// - THEORY.md §VI.1 — generation over composition. A new
    ///   [`ConditionKind`] variant added to `ALL` reaches this
    ///   primitive mechanically through the delegated
    ///   `is_kind_saturated` — a slice that was previously saturated
    ///   (returned `false` here) picks up the new missing variant and
    ///   returns `true` at every downstream `has-any-missing-kind`
    ///   callsite unless it also carries the new variant.
    fn has_any_missing_kind(&self) -> bool {
        !self.is_kind_saturated()
    }

    /// Boolean cardinality-mid-endpoint peer of
    /// [`Self::has_any_missing_kind`] on the closed-set-complement
    /// axis — `true` iff EXACTLY ONE [`ConditionKind::ALL`] variant
    /// appears zero times in this slice (equivalently,
    /// [`Self::missing_kind_count`] `== 1`,
    /// [`Self::missing_kinds`]`.len() == 1`, and
    /// [`Self::first_missing_kind`] equals
    /// [`Self::last_missing_kind`] and is [`Some`]).
    ///
    /// Default body: a two-step-short-circuit closed-set walk over
    /// [`ConditionKind::ALL`] under a negated [`Self::has_kind`]
    /// predicate. Pulls up to two hits off the filtered iterator; the
    /// primitive returns `true` iff the first hit is [`Some`] and the
    /// second is [`None`], WITHOUT materializing
    /// [`Self::missing_kinds`]'s `Vec` and WITHOUT walking every slot
    /// to build [`Self::missing_kind_count`]'s scalar. Short-circuits
    /// at the SECOND missing kind — strictly cheaper than either
    /// widened primitive on every arm with `≥ 2` missing kinds.
    ///
    /// # Peer to [`crate::tagged_union::TaggedUnion::has_unique_missing_kind`]
    ///
    /// Slice-level peer of the tagged-union parent-level
    /// cardinality-mid-endpoint predicate one struct-layer up: where
    /// [`crate::tagged_union::TaggedUnion::has_unique_missing_kind`]
    /// answers "is EXACTLY ONE slot on the tagged-union parent
    /// empty?", `has_unique_missing_kind` answers "does EXACTLY ONE
    /// kind appear in NO condition of the slice?". Both compose
    /// against a two-step-short-circuit closed-set walk under a
    /// negated presence predicate (`!has(kind)` / `!has_kind(kind)`)
    /// at two adjacent typescape sites — the two primitives close the
    /// exactly-one-arm on the closed-set-complement axis at both
    /// struct layers under the SAME shape.
    ///
    /// # Sibling to the Boolean missing-cardinality trichotomy
    ///
    /// Second arm of the `{0, 1, ≥2}` cardinality trichotomy on the
    /// missing axis, closing the natural partition alongside
    /// [`Self::is_kind_saturated`] (zero-arm) and (once its slice-
    /// level peer lands) the many-arm predicate. Every slice
    /// satisfies EXACTLY ONE of the three Boolean projections — the
    /// three primitives partition `0..=ConditionKind::ALL.len()` at
    /// 0, 1, and ≥ 2 respectively. The composition law
    /// `has_unique_missing_kind() == (missing_kind_count() == 1)`
    /// binds the Boolean projection to the scalar primitive at the
    /// trait's default body — swept substrate-wide by
    /// [`assert_slice_refinement_composition_laws`] as its
    /// cardinality-mid-endpoint arm.
    ///
    /// # Semantics
    ///
    /// An empty slice returns `false` on any `N ≥ 2` closed set (every
    /// kind is missing — the fully-missing endpoint, `N` missing not
    /// `1`). A slice carrying `K` distinct kinds for `1 ≤ K ≤ N-2` on
    /// `N ≥ 3` closed sets returns `false` (`N - K ≥ 2` kinds missing).
    /// A slice at the near-saturation arm (carrying every kind except
    /// exactly one) returns `true` — the SOLE arrangement where
    /// `has_unique_missing_kind` returns `true`. A saturated slice
    /// returns `false` (zero missing).
    ///
    /// # Compounding future consumers
    ///
    /// - An operator-facing "one kind away from saturated" fast-path
    ///   discriminator on the near-saturation arm reads
    ///   `boundary.postconditions.has_unique_missing_kind()` at ONE
    ///   call site — one two-step short-circuit walk, no allocation,
    ///   no scalar equality against `1`, byte-for-byte peer of the
    ///   tagged-union `has-unique-missing-kind` classifier one struct-
    ///   layer up under the SAME two-step short-circuit shape.
    /// - A `has-unique-missing-kind` require-tag classifier arm
    ///   reaches this primitive with no allocation, byte-for-byte
    ///   peer of the tagged-union `has-unique-missing-kind` classifier
    ///   one struct-layer up.
    /// - A future gap-analysis diagnostic that prints "one remaining
    ///   ConditionKind not covered by this Boundary" pairs
    ///   `has_unique_missing_kind()` with
    ///   [`Self::first_missing_kind`] to name the SOLE remaining hole
    ///   without allocating [`Self::missing_kinds`]'s `Vec`.
    ///
    /// # Theory grounding
    ///
    /// - THEORY.md §II.1 invariant 5 — composition preserves proofs.
    ///   The cardinality-mid-endpoint projection on the missing axis
    ///   lives at ONE substrate site as a typed two-step-short-
    ///   circuit walk over [`ConditionKind::ALL`] under negated
    ///   [`Self::has_kind`] — byte-for-byte peer of
    ///   `missing_kind_count()` composed against `== 1`, but with a
    ///   second-missing-slot short-circuit that the scalar counter
    ///   primitive does not offer.
    /// - THEORY.md §VI.1 — generation over composition. A new
    ///   [`ConditionKind`] variant added to `ALL` reaches this
    ///   primitive mechanically through the short-circuit walk — a
    ///   slice previously at the near-saturation arm (returned `true`
    ///   here) that omits the new variant now has TWO missing kinds
    ///   and returns `false`; a slice previously at the
    ///   saturated-except-one-of-two arm on an `N == 2` closed set
    ///   remains at the near-saturation arm on `N ≥ 3` iff it
    ///   picks up every OTHER variant.
    fn has_unique_missing_kind(&self) -> bool {
        let mut it = self.iter_missing_kinds();
        it.next().is_some() && it.next().is_none()
    }

    /// Witnessing `Option<ConditionKind>` peer of
    /// [`Self::has_unique_missing_kind`] on the closed-set-complement
    /// axis — `Some(k)` iff `k` is the SOLE [`ConditionKind::ALL`]
    /// variant ABSENT from this slice, else `None`.
    ///
    /// Default body: a two-step-short-circuit fold through
    /// [`Self::iter_missing_kinds`] — pull the first hit; return
    /// `Some(first)` iff the second hit is [`None`], else `None`.
    /// Byte-for-byte peer of
    /// [`crate::tagged_union::TaggedUnion::unique_missing_kind`] one
    /// struct-layer up under the SAME `iter_missing_kinds` two-step
    /// short-circuit shape, and the WITNESSING scalar peer of the
    /// Boolean [`Self::has_unique_missing_kind`] predicate at the SAME
    /// two-step short-circuit shape.
    ///
    /// # Sibling to [`Self::first_missing_kind`] / [`Self::last_missing_kind`]
    ///
    /// FIFTH refinement on the closed-set-complement axis under
    /// exactly-one-hit semantics, `Option<ConditionKind>`-valued:
    /// together with [`Self::first_missing_kind`] and
    /// [`Self::last_missing_kind`] the three primitives project
    /// [`Self::missing_kinds`] onto its cardinality-conditioned scalar
    /// identity on the absent side. The composition laws
    /// `unique_missing_kind().is_some() == (missing_kind_count() == 1)`
    /// and (on the `Some` arm) `unique_missing_kind() ==
    /// first_missing_kind() == last_missing_kind()` bind the exactly-
    /// one scalar identity to the widened primitives at the trait's
    /// default body.
    ///
    /// # Peer to [`Self::unique_distinct_kind`]
    ///
    /// Closed-set-complement peer of the exactly-one-hit scalar on the
    /// closed-set-inversion axis — where `unique_distinct_kind` names
    /// the SOLE PRESENT kind, `unique_missing_kind` names the SOLE
    /// ABSENT kind. The two primitives close the (present, absent) x
    /// (endpoint, exactly-one) 2x3 scalar-Option grid on the slice
    /// level under the SAME two-step short-circuit shape via the
    /// load-bearing iterator peers on the two opposite sides.
    ///
    /// # Semantics
    ///
    /// An empty slice returns `None` on any `N ≥ 2` closed set (every
    /// kind is missing — the fully-missing endpoint, `N` missing not
    /// `1`). A slice at the near-saturation arm (carrying every kind
    /// except exactly one) returns `Some(the-lone-empty)` — the SOLE
    /// arm where `unique_missing_kind` returns `Some` on any `N ≥ 3`
    /// closed set. A saturated slice returns `None` (zero missing).
    ///
    /// # Compounding future consumers
    ///
    /// - An operator-facing "one dependency still unfulfilled: X"
    ///   diagnostic on the near-saturation arm reads
    ///   `boundary.postconditions.unique_missing_kind()` at ONE call
    ///   site — the WITNESS + the exactly-one predicate composed at
    ///   ONE short-circuit walk, rather than pairing the Boolean
    ///   [`Self::has_unique_missing_kind`] with [`Self::first_missing_kind`]
    ///   at TWO independent walks whose agreement is a coincidence.
    /// - A `unique-missing-<kind>` require-tag classifier arm reads
    ///   this primitive with no allocation, byte-for-byte symmetrical
    ///   with `slice.unique_distinct_kind()`.
    /// - A fast-path branch that discriminates "exactly one kind
    ///   still missing" from "0 or ≥ 2 still missing" reads
    ///   `slice.unique_missing_kind().is_some()` at ONE call site.
    ///
    /// # Theory grounding
    ///
    /// - THEORY.md §II.1 invariant 5 — composition preserves proofs.
    ///   The complement-exactly-one-hit witnessing projection lives at
    ///   ONE substrate site as a typed two-step-short-circuit fold
    ///   through the load-bearing [`Self::iter_missing_kinds`] iterator
    ///   — byte-for-byte peer of the tagged-union
    ///   [`crate::tagged_union::TaggedUnion::unique_missing_kind`]
    ///   under the SAME iterator shape.
    /// - THEORY.md §VI.1 — generation over composition. A new
    ///   [`ConditionKind`] variant added to `ALL` reaches this
    ///   primitive mechanically on the missing side.
    fn unique_missing_kind(&self) -> Option<ConditionKind> {
        let mut it = self.iter_missing_kinds();
        let first = it.next()?;
        match it.next() {
            None => Some(first),
            Some(_) => None,
        }
    }

    /// Boolean cardinality "≥ 2" many-arm peer of
    /// [`Self::has_unique_missing_kind`] on the closed-set-complement
    /// axis — `true` iff AT LEAST TWO [`ConditionKind::ALL`] variants
    /// appear zero times in this slice (equivalently,
    /// [`Self::missing_kind_count`] `>= 2` and
    /// [`Self::missing_kinds`]`.len() >= 2`).
    ///
    /// Default body: a two-step-short-circuit closed-set walk over
    /// [`ConditionKind::ALL`] under a negated [`Self::has_kind`]
    /// predicate. Pulls up to two hits off the filtered iterator; the
    /// primitive returns `true` iff BOTH the first and the second are
    /// [`Some`], WITHOUT materializing [`Self::missing_kinds`]'s `Vec`
    /// and WITHOUT walking every slot to build
    /// [`Self::missing_kind_count`]'s scalar. Short-circuits at the
    /// second missing kind — strictly cheaper than either widened
    /// primitive on every arm with `≥ 2` missing kinds. Byte-for-byte
    /// peer of [`crate::tagged_union::TaggedUnion::has_multiple_missing_kinds`]
    /// under the (populated, missing) complement axis one struct-
    /// layer up.
    ///
    /// # Peer to [`crate::tagged_union::TaggedUnion::has_multiple_missing_kinds`]
    ///
    /// Slice-level peer of the tagged-union parent-level cardinality
    /// many-arm predicate one struct-layer up: where
    /// [`crate::tagged_union::TaggedUnion::has_multiple_missing_kinds`]
    /// answers "are AT LEAST TWO slots on the tagged-union parent
    /// empty?", `has_multiple_missing_kinds` answers "do AT LEAST TWO
    /// kinds appear in NO condition of the slice?". Both compose
    /// against a two-step-short-circuit closed-set walk under a
    /// negated presence predicate (`!has(kind)` / `!has_kind(kind)`)
    /// at two adjacent typescape sites — the two primitives close the
    /// at-least-two arm on the closed-set-complement axis at both
    /// struct layers under the SAME shape.
    ///
    /// # Sibling to the Boolean missing-cardinality trichotomy
    ///
    /// Third and final arm of the `{0, 1, ≥2}` cardinality trichotomy
    /// on the missing axis at the slice level, closing the natural
    /// partition alongside [`Self::is_kind_saturated`] (zero-arm) and
    /// [`Self::has_unique_missing_kind`] (one-arm). Every slice
    /// satisfies EXACTLY ONE of the three Boolean projections — the
    /// three primitives partition `0..=ConditionKind::ALL.len()` at
    /// 0, 1, and ≥ 2 respectively. The composition law
    /// `has_multiple_missing_kinds() == (missing_kind_count() >= 2)`
    /// binds the Boolean projection to the scalar primitive at the
    /// trait's default body — swept substrate-wide by
    /// [`assert_slice_refinement_composition_laws`] as its
    /// cardinality-many-arm arm.
    ///
    /// # Semantics
    ///
    /// An empty slice returns `true` on any `N ≥ 2` closed set (every
    /// kind is missing — the fully-missing endpoint, `N ≥ 2` missing).
    /// A slice carrying `K` distinct kinds for `1 ≤ K ≤ N-2` on
    /// `N ≥ 3` closed sets returns `true` (`N - K ≥ 2` kinds missing).
    /// A slice at the near-saturation arm (carrying every kind except
    /// exactly one) returns `false` — the SOLE-missing arrangement
    /// where `has_multiple_missing_kinds` returns `false` (exactly
    /// one missing, not ≥ 2). A saturated slice returns `false`
    /// (zero missing).
    ///
    /// # Compounding future consumers
    ///
    /// - An operator-facing "≥ 2 dependencies still unfulfilled" fast-
    ///   path discriminator on the many-missing arm reads
    ///   `boundary.postconditions.has_multiple_missing_kinds()` at ONE
    ///   call site — one two-step short-circuit walk, no allocation,
    ///   no scalar comparison against `>= 2`, byte-for-byte peer of
    ///   the tagged-union `has-multiple-missing-kinds` classifier one
    ///   struct-layer up under the SAME two-step short-circuit shape.
    /// - A `has-multiple-missing-kinds` require-tag classifier arm
    ///   reaches this primitive with no allocation, byte-for-byte
    ///   peer of the tagged-union `has-multiple-missing-kinds`
    ///   classifier one struct-layer up.
    /// - A future coverage-gap diagnostic that says "≥ 2 remaining
    ///   ConditionKinds not covered by this Boundary" reads
    ///   `has_multiple_missing_kinds()` at ONE call site without
    ///   allocating [`Self::missing_kinds`]'s `Vec`.
    ///
    /// # Theory grounding
    ///
    /// - THEORY.md §II.1 invariant 5 — composition preserves proofs.
    ///   The cardinality-many-arm projection on the missing axis
    ///   lives at ONE substrate site as a typed two-step-short-
    ///   circuit walk over [`ConditionKind::ALL`] under negated
    ///   [`Self::has_kind`] — byte-for-byte peer of
    ///   `missing_kind_count()` composed against `>= 2`, but with a
    ///   second-missing-slot short-circuit that the scalar counter
    ///   primitive does not offer.
    /// - THEORY.md §VI.1 — generation over composition. A new
    ///   [`ConditionKind`] variant added to `ALL` reaches this
    ///   primitive mechanically through the short-circuit walk — a
    ///   slice previously at the near-saturation arm (returned
    ///   `false` here) that omits the new variant now has TWO missing
    ///   kinds and flips to `true`; a slice previously at the
    ///   saturated arm on an `N == 2` closed set that omits the new
    ///   variant flips from `false` to `true` (`1 ≥ 2` false → `1`
    ///   missing on `N == 3`, but this workspace has `N == 8`, so
    ///   the flip surfaces well before the endpoint).
    fn has_multiple_missing_kinds(&self) -> bool {
        let mut it = self.iter_missing_kinds();
        it.next().is_some() && it.next().is_some()
    }

    /// Boolean cardinality "≤ 1" negation peer of
    /// [`Self::has_multiple_missing_kinds`] on the closed-set-complement
    /// axis — `true` iff AT MOST ONE [`ConditionKind::ALL`] variant
    /// appears zero times in this slice (equivalently,
    /// [`Self::missing_kind_count`] `<= 1` and
    /// [`Self::missing_kinds`]`.len() <= 1`). Names the arm where the
    /// slice is SATURATED-OR-NEAR-SATURATED (zero or exactly one kind
    /// missing).
    ///
    /// Default body: `!self.has_multiple_missing_kinds()` — a
    /// definitional Boolean negation of the many-arm primitive. Short-
    /// circuits transitively through
    /// [`Self::has_multiple_missing_kinds`]'s two-step short-circuit
    /// closed-set walk: returns `true` as soon as the many-arm walk
    /// stops with fewer than two missing hits, WITHOUT materializing
    /// [`Self::missing_kinds`]'s `Vec` and WITHOUT walking every slot to
    /// build [`Self::missing_kind_count`]'s scalar. Byte-for-byte peer
    /// of [`crate::tagged_union::TaggedUnion::has_at_most_one_missing_kind`]
    /// under the (populated, missing) complement axis one struct-layer
    /// up, both composed as the same definitional negation of their
    /// respective many-arm primitives.
    ///
    /// # Peer to [`crate::tagged_union::TaggedUnion::has_at_most_one_missing_kind`]
    ///
    /// Slice-level peer of the tagged-union parent-level cardinality
    /// "≤ 1" predicate one struct-layer up: where
    /// [`crate::tagged_union::TaggedUnion::has_at_most_one_missing_kind`]
    /// answers "does the tagged-union parent have AT MOST ONE empty
    /// slot?", `has_at_most_one_missing_kind` answers "do AT MOST ONE
    /// kind appear in NO condition of the slice?". Both compose as the
    /// definitional Boolean negation of their many-arm primitive
    /// (`!has_multiple_missing_kinds()`) at two adjacent typescape
    /// sites — the two primitives close the "≤ 1" arm on the closed-
    /// set-complement axis at both struct layers under the SAME shape.
    ///
    /// # Sibling to the Boolean missing-cardinality pentachotomy
    ///
    /// Fourth arm of the `{0, 1, ≥1, ≤1, ≥2}` Boolean-cardinality
    /// pentachotomy on the missing axis at the slice level, closing
    /// the Boolean-negation grid alongside
    /// [`Self::is_kind_saturated`] (=0 zero-arm),
    /// [`Self::has_unique_missing_kind`] (=1 mid-endpoint),
    /// [`Self::has_any_missing_kind`] (≥1 halfspace), and
    /// [`Self::has_multiple_missing_kinds`] (≥2 many-arm). The
    /// {≤1, ≥2} pair sit on the Boolean-negation axis:
    /// `has_at_most_one_missing_kind == !has_multiple_missing_kinds` on
    /// every arm. The {0, 1} union arm sits on the trichotomy-union
    /// axis: `has_at_most_one_missing_kind == is_kind_saturated ||
    /// has_unique_missing_kind` on every arm. Both composition laws
    /// bind the "≤ 1" Boolean projection to the sibling primitives at
    /// the trait's default body — swept substrate-wide by
    /// [`assert_slice_refinement_composition_laws`] as its "≤ 1" arm.
    ///
    /// # Semantics
    ///
    /// An empty slice returns `false` on any `N ≥ 2` closed set
    /// (every kind is missing — `N ≥ 2` missing, not `≤ 1`).
    /// A slice carrying `K` distinct kinds for `1 ≤ K ≤ N-2` on `N ≥ 3`
    /// closed sets returns `false` (`N - K ≥ 2` kinds missing).
    /// A slice at the near-saturation arm (carrying every kind except
    /// exactly one) returns `true` (exactly 1 missing, `≤ 1`). A
    /// saturated slice returns `true` (0 missing, `≤ 1`) — the union
    /// of the two "≤ 1" arms (`=0` and `=1`) is exactly the
    /// arrangement space where the primitive returns `true`.
    ///
    /// # Compounding future consumers
    ///
    /// - An operator-facing "at most one dependency still unfulfilled"
    ///   fast-path discriminator on the near-saturated / saturated
    ///   arms reads `boundary.postconditions.has_at_most_one_missing_kind()`
    ///   at ONE call site — one bit-flip on the many-arm's two-step
    ///   short-circuit walk, no allocation, no scalar comparison
    ///   against `<= 1`, byte-for-byte peer of the tagged-union
    ///   `has-at-most-one-missing-kind` classifier one struct-layer up
    ///   under the SAME `!has_multiple_missing_kinds` definitional
    ///   negation shape.
    /// - A `has-at-most-one-missing-kind` require-tag classifier arm
    ///   reaches this primitive with no allocation, closing the
    ///   {0, 1, ≥ 2, ≤ 1} cardinality-Boolean grid on the missing axis
    ///   at the slice level alongside its sibling
    ///   `has-multiple-missing-kinds` under the Boolean negation axis.
    /// - A future coverage-gap diagnostic that says "at most one
    ///   remaining ConditionKind not covered by this Boundary" reads
    ///   `has_at_most_one_missing_kind()` at ONE call site without
    ///   allocating [`Self::missing_kinds`]'s `Vec`.
    ///
    /// # Theory grounding
    ///
    /// - THEORY.md §II.1 invariant 5 — composition preserves proofs.
    ///   The cardinality "≤ 1" projection on the missing axis lives
    ///   at ONE substrate site as the definitional Boolean negation
    ///   of [`Self::has_multiple_missing_kinds`]; the three composition
    ///   forms (`!has_multiple_missing_kinds()`, `missing_kind_count() <= 1`,
    ///   and `is_kind_saturated() || has_unique_missing_kind()`)
    ///   compose through the SAME two-step-short-circuit walk shape
    ///   one negation up, byte-for-byte identical on every arm.
    /// - THEORY.md §VI.1 — generation over composition. A new
    ///   [`ConditionKind`] variant added to `ALL` reaches this
    ///   primitive mechanically through the delegated
    ///   [`Self::has_multiple_missing_kinds`] — a slice previously at
    ///   the near-saturation arm (returned `true` here) that omits the
    ///   new variant now has TWO missing kinds and flips to `false`.
    fn has_at_most_one_missing_kind(&self) -> bool {
        !self.has_multiple_missing_kinds()
    }

    /// Boolean per-kind complement of [`Self::has_kind`] — `true` iff
    /// NO [`Condition`] in this slice carries the given
    /// [`ConditionKind`] (equivalently, the kind is a member of
    /// [`Self::missing_kinds`]).
    ///
    /// Default body: `!self.has_kind(kind)` — a definitional negation
    /// of the presence-probe primitive. Short-circuits transitively
    /// through [`Self::has_kind`]'s composition down to
    /// [`Self::iter_kind`]: `!self.find_kind(kind).is_some()` returns
    /// as soon as any match is found (yielding `false`) without
    /// walking the rest of the slice, WITHOUT materializing
    /// [`Self::missing_kinds`]'s `Vec` per-kind for a per-kind
    /// question, and WITHOUT allocating the closed-set-complement scan.
    ///
    /// # Peer to [`crate::tagged_union::TaggedUnion::lacks`]
    ///
    /// Slice-level peer of the tagged-union parent-level closed-set-
    /// complement predicate one struct-layer up: where
    /// [`crate::tagged_union::TaggedUnion::lacks`] answers "is THIS
    /// kind's slot on the tagged-union parent empty?", `lacks_kind`
    /// answers "does THIS kind appear in NO condition of the slice?".
    /// Both compose against their per-kind presence primitive under a
    /// definitional negation (`!has(kind)` / `!has_kind(kind)`) at two
    /// adjacent typescape sites — the two primitives close the
    /// closed-set-complement invariant on the per-kind axis at both
    /// struct layers under the SAME shape.
    ///
    /// # Sibling to [`Self::has_kind`]
    ///
    /// Boolean per-kind complement peer of the point-probe primitive
    /// on the closed-set-complement axis — where `has_kind` returns
    /// `true` iff the addressed kind appears at least once,
    /// `lacks_kind` returns its negation: `true` iff the addressed kind
    /// appears zero times. Together the two Booleans partition the
    /// (slice, kind) matrix at the slice-level presence-probe axis:
    /// exactly one of `has_kind(k)` and `lacks_kind(k)` is `true` for
    /// every `k ∈ ConditionKind::ALL`. The definitional complement law
    /// `lacks_kind(k) == !has_kind(k)` is pinned as a first-class typed
    /// invariant by the trait's own default body and swept substrate-
    /// wide by [`assert_slice_refinement_composition_laws`] as its
    /// per-kind-complement arm.
    ///
    /// # Sibling to [`Self::missing_kinds`] / [`Self::missing_kind_count`]
    ///
    /// Per-kind Boolean projection of the closed-set-complement
    /// widened + scalar primitives — where `missing_kinds` returns the
    /// FULL missing-set (a `Vec<ConditionKind>` of every absent kind)
    /// and `missing_kind_count` returns its cardinality (a `usize` in
    /// `0..=ConditionKind::ALL.len()`), `lacks_kind` collapses the
    /// missing-set to its per-kind membership Boolean for ONE
    /// addressed kind. The composition law
    /// `lacks_kind(k) == missing_kinds().contains(&k)` binds this
    /// Boolean projection to the widened closed-set-complement
    /// primitive at the trait's default body — strictly cheaper than
    /// the widened primitive on every per-kind question because the
    /// negation short-circuits at the first match on the has-side
    /// walk rather than allocating the closed-set-complement scan.
    ///
    /// # Semantics
    ///
    /// An empty slice returns `true` for every [`ConditionKind`] (no
    /// kind appears, so every kind is lacked). A slice carrying kind
    /// `k` at any position returns `false` for `lacks_kind(k)` and
    /// `true` for `lacks_kind(k')` for every `k' ≠ k` (single-kind
    /// coverage). A saturated slice (every kind appears at least once)
    /// returns `false` on every arm — the SOLE arrangement where the
    /// primitive returns `false` for every kind.
    ///
    /// # Compounding future consumers
    ///
    /// - A `lacks-<kind>` require-tag classifier arm reaches this
    ///   primitive with no allocation, byte-for-byte peer of the
    ///   tagged-union `lacks-<kind>` classifier one struct-layer up
    ///   under the SAME `!has(kind)` definitional negation shape.
    /// - A dependency-satisfaction coherence check that enforces "no
    ///   process boundary lacks a `ClosedLoopAuth` postcondition" reads
    ///   `boundary.postconditions.lacks_kind(ConditionKind::ClosedLoopAuth)`
    ///   at ONE call site rather than negating
    ///   `boundary.postconditions.has_kind(ConditionKind::ClosedLoopAuth)`
    ///   at the callsite or materializing the closed-set complement
    ///   with `missing_kinds().contains(&k)`.
    /// - A "still missing: <kind>" diagnostic that reports the FIRST
    ///   unmet postcondition kind reads `slice.lacks_kind(k)` inside a
    ///   `ConditionKind::ALL` fold at ONE substrate primitive per test
    ///   rather than restating the negation body at every callsite.
    ///
    /// # Theory grounding
    ///
    /// - THEORY.md §II.1 invariant 5 — composition preserves proofs.
    ///   The per-kind closed-set-complement projection lives at ONE
    ///   substrate site as a definitional negation of [`Self::has_kind`].
    ///   Every downstream consumer whose semantic reading is "the
    ///   missing set contains THIS kind" reads through this primitive
    ///   rather than negating `has_kind` at every callsite or paying
    ///   for the closed-set-complement scan.
    /// - THEORY.md §VI.1 — generation over composition. A new
    ///   [`ConditionKind`] variant added to `ALL` reaches this
    ///   primitive mechanically through the delegated `has_kind` —
    ///   every downstream `lacks-<kind>` classifier arm sees the wider
    ///   kind set without further per-caller edit.
    fn lacks_kind(&self, kind: ConditionKind) -> bool {
        !self.has_kind(kind)
    }

    /// Kind-scoped strict refinement of [`Self::has_kind`] — `true` iff
    /// the given `kind` appears in the slice AND no OTHER
    /// [`ConditionKind`] appears alongside it. The "exactly this one
    /// variant is present" predicate at the slice level.
    ///
    /// Default body: a FUSED short-circuit closed-set walk over
    /// [`ConditionKind::ALL`] under [`Self::has_kind`] that returns
    /// `false` at the EARLIEST populated slot whose kind is NOT
    /// `kind`, and returns `true` iff the sweep completes with `kind`
    /// seen as the sole populated slot. Byte-for-byte cheaper than
    /// either widened composition
    /// `self.distinct_kinds() == vec![kind]` (which allocates the
    /// distinct-kind Vec before the equality test) or
    /// `self.has_kind(kind) && self.distinct_kind_count() == 1` (which
    /// walks the closed-set twice) on every arm where the slice
    /// carries a populated kind that isn't `kind`.
    ///
    /// # Peer to [`crate::tagged_union::TaggedUnion::has_only`]
    ///
    /// Slice-level peer of the tagged-union parent-level kind-scoped
    /// strict-refinement predicate one struct-layer up: where
    /// [`crate::tagged_union::TaggedUnion::has_only`] answers "is THIS
    /// kind's slot on the tagged-union parent the sole populated
    /// slot?", `has_only_kind` answers "is THIS kind the sole distinct
    /// kind appearing in the slice?". Both primitives compose the SAME
    /// fused short-circuit closed-set walk under a per-kind
    /// [`Self::has_kind`] / `TaggedUnion::has` predicate at two
    /// adjacent typescape sites — the two primitives close the
    /// kind-scoped strict-refinement invariant on the well-formed
    /// (1-of-N populated) arm at both struct layers under the SAME
    /// shape.
    ///
    /// # Sibling to [`Self::has_kind`]
    ///
    /// Kind-scoped strict-refinement peer of the point-probe primitive
    /// on the closed-set-inversion axis — where `has_kind(k)` returns
    /// `true` iff `k` appears at least once (multiplicity ignored),
    /// `has_only_kind(k)` refines that to the strictly stricter
    /// predicate "k appears AND no other kind appears". The
    /// implication chain `has_only_kind(k) ⟹ has_kind(k)` is a
    /// definitional consequence of the fused walk's `saw_kind = true`
    /// arm; the reverse is FALSE on any partially-populated slice
    /// where a second kind lives alongside `k`. The composition law
    /// `has_only_kind(k) == (distinct_kinds() == vec![k])` binds this
    /// primitive to the widened closed-set-inversion primitive at the
    /// trait's default body — swept substrate-wide by
    /// [`assert_slice_refinement_composition_laws`] as its kind-scoped
    /// strict-refinement arm.
    ///
    /// # Truth table on the slice-level closed-set-inversion contract
    ///
    /// For a slice with `ConditionKind::ALL` of cardinality `N ≥ 2`
    /// and a fixed argument `kind`:
    ///
    /// - Empty slice (0 conditions, distinct-kind set empty): `false`
    ///   on any `N ≥ 2` — no kind appears, so `kind` isn't the sole
    ///   populated kind.
    /// - Single-populated slice with populated kind `p` (1 condition,
    ///   distinct-kind set `{p}`): `has_only_kind(kind) == (kind == p)`.
    /// - Duplicate-populated slice with kind `p` at every position
    ///   (multiplicity > 1, distinct-kind set `{p}`): still
    ///   `has_only_kind(kind) == (kind == p)` — MULTIPLICITY IS
    ///   IGNORED on the populated side (byte-for-byte with `has_kind`'s
    ///   multiplicity behavior).
    /// - Two-kinds slice with kinds `{p, q}` where `p != q` (distinct-
    ///   kind set `{p, q}`): `false` for every kind — the strict
    ///   refinement fails at the earliest walk step that hits the
    ///   second kind.
    /// - Saturated slice (every kind appears): `false` for every kind
    ///   on any `N ≥ 2` — N distinct kinds populate, so no single
    ///   kind is "only".
    ///
    /// # Kind-domain exhaustivity
    ///
    /// A slice satisfies `has_only_kind(k)` for AT MOST one `k`, since
    /// two distinct kinds cannot both be the sole distinct populated
    /// kind. On the well-formed arm the count is exactly 1 (the
    /// addressed populated kind); on every other arm the count is 0.
    /// This kind-domain exhaustivity law binds the argument-scoped
    /// projection to the parent-scoped cardinality primitive
    /// `distinct_kind_count() == 1` at the composition-law surface.
    ///
    /// # Compounding future consumers
    ///
    /// - A `has-only-<kind>` require-tag classifier arm reaches this
    ///   primitive with no allocation, byte-for-byte peer of the
    ///   tagged-union `has-only-<kind>` classifier one struct-layer up
    ///   under the SAME fused short-circuit walk shape.
    /// - A coherence check verifying "every ephemeral spec whose
    ///   postconditions carry ONLY `ClosedLoopAuth` (no
    ///   `JobAttested`, no `Cel`, ...) is a well-formed closed-loop
    ///   probe" reads
    ///   `spec.postconditions.has_only_kind(ConditionKind::ClosedLoopAuth)`
    ///   at ONE call site — strictly cheaper than reaching for the
    ///   widened composition on every well-formed-diagonal question.
    /// - An operator-facing "unambiguously kind=<k>" diagnostic on
    ///   the slice-level probe reads `slice.has_only_kind(k)` after
    ///   `first_distinct_kind` names the sole populated kind — one
    ///   fused walk, no allocation, no `Option<ConditionKind>`
    ///   construction.
    ///
    /// # Theory grounding
    ///
    /// - THEORY.md §II.1 invariant 5 — composition preserves proofs.
    ///   The kind-scoped strict-refinement projection lives at ONE
    ///   substrate site as a fused short-circuit walk over
    ///   [`ConditionKind::ALL`] under [`Self::has_kind`] with early
    ///   exit on the first populated slot whose kind is not `kind` —
    ///   byte-for-byte cheaper than the widened composition
    ///   `distinct_kinds() == vec![kind]`, semantically identical on
    ///   every arm.
    /// - THEORY.md §VI.1 — generation over composition. A new
    ///   [`ConditionKind`] variant added to `ALL` reaches this
    ///   primitive mechanically through the fused walk — every
    ///   downstream `has-only-<kind>` classifier arm sees the wider
    ///   kind set without further per-caller edit.
    fn has_only_kind(&self, kind: ConditionKind) -> bool {
        let mut saw_kind = false;
        for k in ConditionKind::ALL {
            if !self.has_kind(k) {
                continue;
            }
            if k == kind {
                saw_kind = true;
            } else {
                return false;
            }
        }
        saw_kind
    }

    /// Kind-scoped strict refinement of [`Self::lacks_kind`] — `true` iff
    /// the given `kind` does NOT appear in the slice AND every OTHER
    /// [`ConditionKind`] DOES appear at least once. The "exactly this
    /// one variant is the sole hole" predicate at the slice level.
    ///
    /// Default body: a FUSED short-circuit closed-set walk over
    /// [`ConditionKind::ALL`] under [`Self::has_kind`] that skips every
    /// populated slot, returns `false` at the EARLIEST missing slot
    /// whose kind is NOT `kind`, and returns `true` iff the sweep
    /// completes with `kind` seen as the sole missing slot. Byte-for-
    /// byte cheaper than either widened composition
    /// `self.missing_kinds() == vec![kind]` (which allocates the
    /// missing-kind Vec before the equality test) or
    /// `self.lacks_kind(kind) && self.missing_kind_count() == 1` (which
    /// walks the closed-set-complement scan twice) on every arm where
    /// the slice carries a missing kind that isn't `kind`.
    ///
    /// # Peer to [`crate::tagged_union::TaggedUnion::lacks_only`]
    ///
    /// Slice-level peer of the tagged-union parent-level kind-scoped
    /// strict-refinement predicate on the missing axis one struct-layer
    /// up: where
    /// [`crate::tagged_union::TaggedUnion::lacks_only`] answers "is THIS
    /// kind's slot on the tagged-union parent the sole empty slot?",
    /// `lacks_only_kind` answers "is THIS kind the sole missing kind
    /// from the slice's distinct set?". Both primitives compose the
    /// SAME fused short-circuit closed-set walk under a per-kind
    /// [`Self::has_kind`] / `TaggedUnion::has` predicate at two adjacent
    /// typescape sites — the two primitives close the kind-scoped
    /// strict-refinement invariant on the near-saturation-diagonal
    /// (`N-1`-of-N populated with the sole hole at `kind`) arm at both
    /// struct layers under the SAME shape.
    ///
    /// # Sibling to [`Self::has_only_kind`]
    ///
    /// Closed-set-complement mirror of the well-formed-diagonal
    /// strict-refinement primitive on the populated axis — where
    /// `has_only_kind(k)` returns `true` iff `k` is the sole distinct
    /// populated kind, `lacks_only_kind(k)` returns `true` iff `k` is
    /// the sole missing kind. Together the two peers CLOSE the
    /// (populated, missing) × (subset, equal) 2x2 kind-scoped
    /// strict-refinement grid at the slice level alongside `has_kind`
    /// (populated subset) and `lacks_kind` (missing subset).
    ///
    /// # Truth table on the slice-level closed-set-complement contract
    ///
    /// For a slice with `ConditionKind::ALL` of cardinality `N ≥ 2`
    /// and a fixed argument `kind`:
    ///
    /// - Empty slice (0 conditions, distinct-kind set empty,
    ///   missing-kind set == ALL): `false` on any `N ≥ 2` — every kind
    ///   is missing, so `kind` is NOT the sole missing kind.
    /// - Single-populated slice with populated kind `p` (1 condition,
    ///   missing-kind set == `ALL \ {p}`): `false` on any `N ≥ 3`
    ///   (`N - 1 ≥ 2` missing kinds, no sole missing kind); on `N == 2`
    ///   the missing set is `{q}` where `q ≠ p`, so
    ///   `lacks_only_kind(kind) == (kind == q)`.
    /// - Near-saturation slice with populated kinds `ALL \ {q}` (each
    ///   kind except `q` populated, missing set `{q}`): the SOLE `true`
    ///   arm — `lacks_only_kind(kind) == (kind == q)`.
    /// - Saturated slice (every kind appears): `false` on every kind —
    ///   no kind is missing, so no kind is the sole missing kind.
    /// - Multiplicity is ignored on the populated side: a slice
    ///   carrying `k` at every position still has an empty missing set,
    ///   or a missing set `{k'}` where `k' ≠ k`, byte-for-byte with
    ///   the single-populated arrangement.
    ///
    /// # Kind-domain exhaustivity
    ///
    /// A slice satisfies `lacks_only_kind(k)` for AT MOST one `k`,
    /// since two distinct kinds cannot both be the sole missing kind.
    /// On the near-saturation arm the count is exactly 1 (the sole
    /// missing kind); on every other arm the count is 0. This
    /// kind-domain exhaustivity law binds the argument-scoped
    /// projection to the parent-scoped cardinality primitive
    /// `missing_kind_count() == 1` at the composition-law surface.
    ///
    /// # Compounding future consumers
    ///
    /// - A `lacks-only-<kind>` require-tag classifier arm reaches this
    ///   primitive with no allocation, byte-for-byte peer of the
    ///   tagged-union `lacks-only-<kind>` classifier one struct-layer
    ///   up under the SAME fused short-circuit walk shape.
    /// - A "one dependency short: <kind>" diagnostic on the aggregate
    ///   boundary check reads
    ///   `slice.lacks_only_kind(k)` at ONE call site — one fused
    ///   short-circuit walk, no allocation, strictly cheaper than
    ///   `slice.first_missing_kind() == Some(k) && slice.missing_kind_count() == 1`
    ///   which walks the closed-set-complement scan twice.
    /// - A coherence check that verifies "the near-saturation slice
    ///   from an `all_but_one_kind_of(k)` factory is unambiguously
    ///   missing kind `k`" reads `slice.lacks_only_kind(k)` at ONE
    ///   site — the strongest structural pin on the missing-side
    ///   well-formed diagonal.
    ///
    /// # Theory grounding
    ///
    /// - THEORY.md §II.1 invariant 5 — composition preserves proofs.
    ///   The kind-scoped strict-refinement projection on the missing
    ///   axis lives at ONE substrate site as a fused short-circuit
    ///   walk over [`ConditionKind::ALL`] under [`Self::has_kind`]
    ///   with early exit on the first missing slot whose kind is not
    ///   `kind` — byte-for-byte peer of [`Self::has_only_kind`]'s
    ///   fused walk under complement, semantically identical to
    ///   `first_missing_kind() == Some(kind) && missing_kind_count() == 1`
    ///   on every arm.
    /// - THEORY.md §VI.1 — generation over composition. A new
    ///   [`ConditionKind`] variant added to `ALL` reaches this
    ///   primitive mechanically through the delegated `has_kind` walk
    ///   — every downstream `lacks-only-<kind>` classifier arm sees
    ///   the wider kind set without further per-caller edit.
    fn lacks_only_kind(&self, kind: ConditionKind) -> bool {
        let mut saw_kind = false;
        for k in ConditionKind::ALL {
            if self.has_kind(k) {
                continue;
            }
            if k == kind {
                saw_kind = true;
            } else {
                return false;
            }
        }
        saw_kind
    }

    /// Boolean cardinality "≥ 2" many-arm peer of [`Self::has_kind`]
    /// (≥ 1) and [`Self::lacks_kind`] (= 0) on the per-kind count axis
    /// — `true` iff AT LEAST TWO [`Condition`] values with the given
    /// `kind` appear in this slice (equivalently,
    /// [`Self::count_kind`]`(kind) >= 2` and
    /// [`Self::iter_kind`]`(kind).count() >= 2`).
    ///
    /// Default body: a two-step-short-circuit walk over
    /// [`Self::iter_kind`]`(kind)` — pulls up to two hits off the
    /// load-bearing per-kind iterator; the primitive returns `true`
    /// iff BOTH the first and the second are [`Some`], WITHOUT
    /// walking every slot to build [`Self::count_kind`]'s scalar.
    /// Short-circuits at the second matching condition — strictly
    /// cheaper than [`Self::count_kind`]`(kind) >= 2` on every arm
    /// with `≥ 2` matches. Byte-for-byte peer of
    /// [`Self::has_multiple_distinct_kinds`] under the (distinct-
    /// kinds axis, per-kind matches axis) parity: both compose the
    /// SAME two-step short-circuit shape one iterator over.
    ///
    /// # Sibling to [`Self::lacks_kind`] / [`Self::has_kind`] / [`Self::count_kind`]
    ///
    /// Many-arm on the per-kind count axis alongside
    /// [`Self::lacks_kind`] (= 0 zero-endpoint) and
    /// [`Self::has_kind`] (≥ 1 halfspace) — the three Booleans
    /// project [`Self::count_kind`]`(kind)`'s scalar onto its
    /// {= 0, ≥ 1, ≥ 2} arms. The composition law
    /// `has_multiple_of_kind(k) == (count_kind(k) >= 2)` binds the
    /// per-kind many-arm Boolean projection to the scalar counter
    /// primitive at the trait's default body — swept substrate-wide
    /// by [`assert_slice_refinement_composition_laws`] as its per-
    /// kind many-arm arm.
    ///
    /// # Semantics
    ///
    /// An empty slice returns `false` on every kind (0 matches, not
    /// `≥ 2`). A slice carrying `kind` exactly once (with any other
    /// kinds in any multiplicity) returns `false` on THAT kind (1
    /// match). A slice carrying `kind` two or more times returns
    /// `true` on THAT kind. Multiplicity of OTHER kinds is
    /// irrelevant — the primitive projects the slice onto the per-
    /// kind count axis for the queried kind alone.
    ///
    /// # Compounding future consumers
    ///
    /// - A boundary-well-formedness coherence check that rejects a
    ///   Process whose preconditions carry duplicate
    ///   [`ConditionKind::ProcessPhase`] entries reads
    ///   `boundary.preconditions.has_multiple_of_kind(ConditionKind::ProcessPhase)`
    ///   at ONE call site — one two-step short-circuit walk, no
    ///   allocation, no scalar comparison against `>= 2`.
    /// - A `has-multiple-of-<kind>` require-tag classifier arm reads
    ///   this primitive with no allocation, byte-for-byte peer of the
    ///   whole-slice `has-multiple-distinct-kinds` classifier one
    ///   axis over under the SAME two-step short-circuit shape.
    /// - A fleet-wide "duplicate condition detected" audit dump reads
    ///   `ConditionKind::ALL.into_iter().filter(|k|
    ///   slice.has_multiple_of_kind(*k))` at ONE call site.
    ///
    /// # Theory grounding
    ///
    /// - THEORY.md §II.1 invariant 5 — composition preserves proofs.
    ///   The per-kind cardinality-many-arm projection on the count
    ///   axis lives at ONE substrate site as a typed two-step-short-
    ///   circuit fold through the load-bearing [`Self::iter_kind`]
    ///   iterator — byte-for-byte peer of `count_kind(kind)` composed
    ///   against `>= 2`, but with a second-match short-circuit that
    ///   the scalar counter primitive does not offer.
    /// - THEORY.md §VI.1 — generation over composition. A new
    ///   [`ConditionKind`] variant added to `ALL` reaches this
    ///   primitive mechanically through the per-kind iterator — a
    ///   slice previously containing no conditions of the new kind
    ///   returns `false` on it here, and picks up `true` the moment
    ///   an operator authors a second matching condition.
    fn has_multiple_of_kind(&self, kind: ConditionKind) -> bool {
        let mut it = self.iter_kind(kind);
        it.next().is_some() && it.next().is_some()
    }

    /// Boolean cardinality "= 1" middle-arm peer of [`Self::lacks_kind`]
    /// (= 0) and [`Self::has_multiple_of_kind`] (≥ 2) on the per-kind
    /// count axis — `true` iff EXACTLY ONE [`Condition`] with the given
    /// `kind` appears in this slice (equivalently,
    /// [`Self::count_kind`]`(kind) == 1` and
    /// [`Self::iter_kind`]`(kind).count() == 1`). Closes the {= 0,
    /// = 1, ≥ 2} per-kind cardinality Boolean trichotomy at the slice
    /// level; every state maps to EXACTLY ONE of the three arms.
    ///
    /// Default body: a two-step-short-circuit walk over
    /// [`Self::iter_kind`]`(kind)` — pulls up to two hits off the load-
    /// bearing per-kind iterator; the primitive returns `true` iff the
    /// first is [`Some`] AND the second is [`None`], WITHOUT walking
    /// every slot to build [`Self::count_kind`]'s scalar. Short-
    /// circuits at the second matching condition — strictly cheaper
    /// than [`Self::count_kind`]`(kind) == 1` on every arm with `≥ 2`
    /// matches (the primitive returns `false` on the second hit
    /// without pulling further). Byte-for-byte peer of
    /// [`Self::has_multiple_of_kind`] under the (= 1, ≥ 2) count-axis
    /// duality: both compose the SAME two-step short-circuit walk
    /// shape, differing only in the second-hit predicate
    /// ([`Option::is_none`] here vs [`Option::is_some`] on the many-
    /// arm peer).
    ///
    /// # Sibling to [`Self::lacks_kind`] / [`Self::has_kind`] /
    /// [`Self::has_multiple_of_kind`] / [`Self::count_kind`]
    ///
    /// Middle arm on the per-kind count trichotomy alongside
    /// [`Self::lacks_kind`] (= 0 zero-endpoint) and
    /// [`Self::has_multiple_of_kind`] (≥ 2 many-arm) — the three
    /// Booleans PARTITION the per-kind cardinality scalar's non-
    /// negative-integer arms: EXACTLY ONE of the three returns `true`
    /// on any given `(slice, kind)` pair. Peer of the tagged-union
    /// parent-level [`crate::tagged_union::TaggedUnion::has_unique_populated_kind`]
    /// on the whole-parent count axis one struct layer up (single
    /// populated slot vs single condition of a given kind). The
    /// composition laws
    /// `has_unique_of_kind(k) == (count_kind(k) == 1)`,
    /// `has_unique_of_kind(k) == (iter_kind(k).count() == 1)`, and
    /// `has_unique_of_kind(k) == { iter_kind(k) two-step short-circuit }`
    /// bind the per-kind mid-endpoint Boolean projection to the
    /// scalar counter primitive at the trait's default body — swept
    /// substrate-wide by [`assert_slice_refinement_composition_laws`]
    /// as its per-kind mid-endpoint arm alongside the existing per-
    /// kind many-arm pin.
    ///
    /// # Semantics
    ///
    /// An empty slice returns `false` on every kind (0 matches, not
    /// `= 1`). A slice carrying `kind` exactly once (with any other
    /// kinds in any multiplicity) returns `true` on THAT kind. A
    /// slice carrying `kind` two or more times returns `false` on
    /// THAT kind. Multiplicity of OTHER kinds is irrelevant — the
    /// primitive projects the slice onto the per-kind count axis for
    /// the queried kind alone. Together with `lacks_kind` and
    /// `has_multiple_of_kind`, the three arms cover every non-
    /// negative multiplicity: `lacks_kind(k)` ↔ 0 matches,
    /// `has_unique_of_kind(k)` ↔ 1 match, `has_multiple_of_kind(k)`
    /// ↔ ≥ 2 matches.
    ///
    /// # Compounding future consumers
    ///
    /// - A boundary-well-formedness coherence check that enforces
    ///   "every Process's preconditions carry EXACTLY ONE
    ///   [`ConditionKind::ProcessPhase`] entry" reads
    ///   `boundary.preconditions.has_unique_of_kind(ConditionKind::ProcessPhase)`
    ///   at ONE call site — one two-step short-circuit walk, no
    ///   allocation, no scalar comparison against `== 1`.
    /// - A `has-unique-of-<kind>` require-tag classifier arm reads
    ///   this primitive with no allocation, byte-for-byte peer of
    ///   `has-multiple-of-<kind>` under the SAME two-step short-
    ///   circuit shape.
    /// - A fleet-wide "exactly-one-of-kind detected" audit dump reads
    ///   `ConditionKind::ALL.into_iter().filter(|k|
    ///   slice.has_unique_of_kind(*k))` at ONE call site.
    /// - A future authoring-time linter that surfaces "operator
    ///   intended a singleton condition but ended up with 0 or ≥ 2
    ///   entries" reaches the three-arm partition through
    ///   `!slice.has_unique_of_kind(k)` for the negative arm and
    ///   drills down to the specific missing/duplicate case through
    ///   `slice.lacks_kind(k)` or `slice.has_multiple_of_kind(k)`
    ///   without restating the walk.
    ///
    /// # Theory grounding
    ///
    /// - THEORY.md §II.1 invariant 5 — composition preserves proofs.
    ///   The per-kind cardinality-mid-endpoint projection on the
    ///   count axis lives at ONE substrate site as a typed two-step-
    ///   short-circuit fold through the load-bearing [`Self::iter_kind`]
    ///   iterator — byte-for-byte peer of `count_kind(kind)` composed
    ///   against `== 1`, but with a second-match short-circuit that
    ///   the scalar counter primitive does not offer.
    /// - THEORY.md §VI.1 — generation over composition. A new
    ///   [`ConditionKind`] variant added to `ALL` reaches this
    ///   primitive mechanically through the per-kind iterator — a
    ///   slice previously containing no conditions of the new kind
    ///   returns `false` on it here, and picks up `true` the moment
    ///   an operator authors exactly ONE matching condition (and
    ///   returns to `false` the moment a second one appears).
    fn has_unique_of_kind(&self, kind: ConditionKind) -> bool {
        let mut it = self.iter_kind(kind);
        it.next().is_some() && it.next().is_none()
    }

    /// Boolean cardinality "≤ 1" negation peer of
    /// [`Self::has_multiple_of_kind`] on the per-kind count axis —
    /// `true` iff AT MOST ONE [`Condition`] with the given `kind`
    /// appears in this slice (equivalently, [`Self::count_kind`]
    /// `(kind) <= 1` and [`Self::iter_kind`]`(kind).count() <= 1`).
    /// Closes the {= 0, = 1, ≥ 1, ≥ 2, ≤ 1} Boolean-cardinality grid
    /// on the per-kind axis at the slice level alongside its sibling
    /// [`Self::has_multiple_of_kind`] (≥ 2 many-arm) under the
    /// definitional negation `!(≥ 2) == (≤ 1)`, and alongside
    /// `!has_kind` (= 0 zero-endpoint) OR [`Self::has_unique_of_kind`]
    /// (= 1 mid-endpoint) as the trichotomy-union arm. Names the
    /// per-kind arrangement space where the slice is
    /// EMPTY-OR-SINGLETON for that kind (zero or exactly one match).
    ///
    /// Default body: `!self.has_multiple_of_kind(kind)` — a
    /// definitional Boolean negation of the many-arm primitive.
    /// Short-circuits transitively through
    /// [`Self::has_multiple_of_kind`]'s two-step short-circuit walk
    /// over [`Self::iter_kind`]: returns `true` as soon as the many-
    /// arm walk stops with fewer than two matches, WITHOUT walking
    /// every slot to build [`Self::count_kind`]'s scalar. Strictly
    /// cheaper than [`Self::count_kind`]`(kind) <= 1` on every arm
    /// with `≥ 2` matches (short-circuits at the second hit rather
    /// than counting further). Byte-for-byte peer of
    /// [`Self::has_at_most_one_distinct_kind`] and
    /// [`Self::has_at_most_one_missing_kind`] under the (distinct,
    /// missing, per-kind) parity: all three compose the SAME
    /// definitional negation shape (`!has_multiple_*`) at the slice-
    /// level trait's default body, differing only in the many-arm
    /// primitive they negate.
    ///
    /// # Peer to [`Self::has_at_most_one_distinct_kind`] / [`Self::has_at_most_one_missing_kind`]
    ///
    /// Third axis of the slice-level "≤ 1" negation triad. The
    /// distinct-axis peer negates the "≥ 2 distinct kinds present"
    /// many-arm; the missing-axis peer negates the "≥ 2 kinds
    /// missing" many-arm; this per-kind peer negates the "≥ 2
    /// matches of a specific kind" many-arm. Together the three
    /// close the "≤ 1" arm on every cardinality axis
    /// (distinct-kind, missing-kind, per-kind count) at the SAME
    /// slice-level trait under the SAME definitional negation shape.
    ///
    /// # Sibling to the per-kind Boolean cardinality tetrachotomy
    ///
    /// Fourth arm of the `{= 0, ≥ 1, = 1, ≥ 2, ≤ 1}` Boolean-
    /// cardinality closure on the per-kind axis at the slice level,
    /// closing the Boolean-negation grid alongside
    /// [`Self::lacks_kind`] (= 0 zero-endpoint),
    /// [`Self::has_unique_of_kind`] (= 1 mid-endpoint),
    /// [`Self::has_kind`] (≥ 1 halfspace), and
    /// [`Self::has_multiple_of_kind`] (≥ 2 many-arm). The {≤ 1, ≥ 2}
    /// pair sit on the Boolean-negation axis:
    /// `has_at_most_one_of_kind(k) == !has_multiple_of_kind(k)` on
    /// every arm. The {0, 1} union arm sits on the trichotomy-union
    /// axis: `has_at_most_one_of_kind(k) == lacks_kind(k) ||
    /// has_unique_of_kind(k)` on every arm. Both composition laws
    /// bind the per-kind "≤ 1" Boolean projection to the sibling
    /// primitives at the trait's default body — swept substrate-wide
    /// by [`assert_slice_refinement_composition_laws`] as its per-
    /// kind "≤ 1" arm alongside the existing per-kind zero-endpoint,
    /// mid-endpoint, halfspace, and many-arm pins.
    ///
    /// # Semantics
    ///
    /// An empty slice returns `true` on every kind (0 matches, `≤ 1`).
    /// A slice carrying `kind` exactly once (with any other kinds in
    /// any multiplicity) returns `true` on THAT kind. A slice
    /// carrying `kind` two or more times returns `false` on THAT
    /// kind. Multiplicity of OTHER kinds is irrelevant — the
    /// primitive projects the slice onto the per-kind count axis for
    /// the queried kind alone. Together with `lacks_kind` and
    /// `has_unique_of_kind`, the "≤ 1" arm equals their union:
    /// `has_at_most_one_of_kind(k) ↔ lacks_kind(k) ∨
    /// has_unique_of_kind(k)`.
    ///
    /// # Compounding future consumers
    ///
    /// - A boundary-well-formedness coherence check that enforces
    ///   "every Process's preconditions carry AT MOST ONE
    ///   [`ConditionKind::ProcessPhase`] entry" (allowing zero, but
    ///   rejecting duplicates) reads
    ///   `boundary.preconditions.has_at_most_one_of_kind(ConditionKind::ProcessPhase)`
    ///   at ONE call site — one bit-flip on the many-arm's two-step
    ///   short-circuit walk, no allocation, no scalar comparison
    ///   against `<= 1`. Byte-for-byte peer of the same coherence
    ///   check phrased with `!slice.has_multiple_of_kind(k)` at the
    ///   callsite, but reads the intent as "at most one" directly.
    /// - A `has-at-most-one-of-<kind>` require-tag classifier arm
    ///   reaches this primitive with no allocation, closing the
    ///   {= 0, = 1, ≥ 1, ≥ 2, ≤ 1} cardinality-Boolean grid on the
    ///   per-kind axis at the slice level alongside its sibling
    ///   `has-multiple-of-<kind>` under the Boolean negation axis.
    /// - A fleet-wide "no duplicate condition of kind detected"
    ///   audit dump reads `ConditionKind::ALL.into_iter().filter(|k|
    ///   slice.has_at_most_one_of_kind(*k))` at ONE call site
    ///   without materializing the negation at every callsite.
    /// - A future authoring-time linter that surfaces "operator's
    ///   condition slice has no duplicates for any kind" reads
    ///   `ConditionKind::ALL.into_iter().all(|k|
    ///   slice.has_at_most_one_of_kind(k))` — the whole-slice "no
    ///   kind is duplicated" projection composes through the SAME
    ///   substrate primitive without restating the negation.
    ///
    /// # Theory grounding
    ///
    /// - THEORY.md §II.1 invariant 5 — composition preserves proofs.
    ///   The per-kind cardinality "≤ 1" projection lives at ONE
    ///   substrate site as the definitional Boolean negation of
    ///   [`Self::has_multiple_of_kind`]; the three composition forms
    ///   (`!has_multiple_of_kind(k)`, `count_kind(k) <= 1`, and
    ///   `lacks_kind(k) || has_unique_of_kind(k)`) compose through
    ///   the SAME two-step-short-circuit walk shape one negation up,
    ///   byte-for-byte identical on every arm.
    /// - THEORY.md §VI.1 — generation over composition. A new
    ///   [`ConditionKind`] variant added to `ALL` reaches this
    ///   primitive mechanically through the delegated
    ///   [`Self::has_multiple_of_kind`] — a slice previously at the
    ///   empty or singleton arm (returned `true` here) that picks up
    ///   a second condition of the new variant now has TWO matches
    ///   and flips to `false`.
    fn has_at_most_one_of_kind(&self, kind: ConditionKind) -> bool {
        !self.has_multiple_of_kind(kind)
    }

    /// Returns the unique [`Condition`] of the given [`ConditionKind`]
    /// in this slice, or [`None`] if zero or more than one such
    /// [`Condition`] exists — the `Option<&Condition>` witnessing
    /// refinement of the Boolean [`Self::has_unique_of_kind`] on the
    /// per-kind count axis at the slice level. Default body: a two-
    /// step short-circuit walk over [`Self::iter_kind`] — pulls at
    /// most two matches, returns the first iff no second exists.
    ///
    /// # Sibling to [`Self::has_unique_of_kind`]
    ///
    /// One refinement wider: `has_unique_of_kind` collapses the return
    /// to a `bool`; `unique_of_kind` returns the matching
    /// `&Condition` so callers can read [`Condition::params`] without
    /// a two-pass has+find dance. The composition laws
    /// `has_unique_of_kind(k) == unique_of_kind(k).is_some()` and
    /// `unique_of_kind(k).map(|c| c.kind) == Some(k)` (when
    /// `has_unique_of_kind(k)`, else `None`) bind the Boolean
    /// projection to the widened witness at the trait's default body.
    ///
    /// # Peer to [`Self::unique_distinct_kind`] / [`Self::unique_missing_kind`]
    ///
    /// Third `Option`-witnessing peer on the slice-level Boolean
    /// mid-endpoint algebra: `unique_distinct_kind` witnesses the
    /// singleton-populated-distinct arm (`Option<ConditionKind>`),
    /// `unique_missing_kind` witnesses the singleton-missing arm
    /// (`Option<ConditionKind>`), and this per-kind peer witnesses
    /// the singleton-per-kind arm (`Option<&Condition>`). All three
    /// collapse `has_unique_*` Booleans to a single-walk `Option`
    /// witness of the singleton arm; a regression that drifted any
    /// witness from its Boolean sibling surfaces at the substrate's
    /// composition-law testkit.
    ///
    /// # Semantics
    ///
    /// An empty slice returns [`None`] on every kind. A slice
    /// carrying `kind` exactly once returns `Some(&c)` for that `c`.
    /// A slice carrying `kind` two or more times returns [`None`]
    /// (multiple witnesses collapse to no witness — the
    /// `Option<&Condition>` refinement expresses "there is exactly
    /// one match, and here it is" as a single type-carried
    /// invariant). Multiplicity of other kinds is irrelevant.
    ///
    /// # Compounding
    ///
    /// A coherence check that verifies "if exactly one
    /// [`ConditionKind::PromQL`] precondition, its params must
    /// contain `expr`" reads
    /// `slice.unique_of_kind(ConditionKind::PromQL).map(check_params)`
    /// at ONE call site — one walk, no allocation, no two-pass
    /// `has_unique_of_kind` + `find_kind` dance that would walk the
    /// slice twice. A future operator-facing diagnostic that surfaces
    /// "the unique JobAttested condition's params" reads
    /// `spec.postconditions.unique_of_kind(JobAttested)` and unwraps
    /// the params directly — a two-pass phrase leaves the singleton
    /// invariant implicit; this peer carries it in the return type.
    ///
    /// # Theory grounding
    ///
    /// - THEORY.md §II.1 invariant 5 — composition preserves proofs.
    ///   The `Option<&Condition>` witnessing refinement lives at ONE
    ///   substrate site as a two-step short-circuit walk over
    ///   [`Self::iter_kind`]; the composition law
    ///   `has_unique_of_kind(k) == unique_of_kind(k).is_some()` binds
    ///   the Boolean projection to the widened witness at the trait's
    ///   default body.
    /// - THEORY.md §VI.1 — generation over composition. A new
    ///   [`ConditionKind`] variant reaches this primitive
    ///   mechanically through the delegated [`Self::iter_kind`] with
    ///   no per-caller edit.
    fn unique_of_kind(&self, kind: ConditionKind) -> Option<&Condition> {
        let mut it = self.iter_kind(kind);
        let first = it.next()?;
        match it.next() {
            None => Some(first),
            Some(_) => None,
        }
    }
}

/// Iterator yielded by [`ConditionSliceExt::iter_kind`] — the widened
/// primitive on the slice-level presence-probe axis. Wraps a
/// [`std::slice::Iter`] over `Condition` values with a
/// [`ConditionKind`] discriminator; [`Iterator::next`] short-circuits
/// via [`std::iter::Iterator::find`] on the wrapped iterator so the
/// filter walk is byte-identical to `self.iter().filter(|c| c.kind ==
/// kind).next()` without paying for the anonymous-closure type
/// erasure a chained-adapter return position would carry.
///
/// # Why a named type
///
/// [`ConditionSliceExt::iter_kind`] returns this concrete type rather
/// than `impl Iterator<Item = &Condition>` so downstream consumers
/// (a fleet-wide audit dump that stores match streams in a struct
/// field, a coherence check that composes the iterator against
/// [`std::iter::Chain`] across pre-/post-conditions) name the
/// primitive's return without pulling in RPITIT's unnameable
/// per-callsite type. [`Boundary::iter_condition_kind`] and
/// [`crate::ephemeral::EphemeralSpec::iter_condition_kind`] chain two
/// [`KindMatches`] iterators via [`Iterator::chain`] — the resulting
/// [`std::iter::Chain<KindMatches<'_>, KindMatches<'_>>`] is itself
/// a standard nameable type.
pub struct KindMatches<'a> {
    inner: std::slice::Iter<'a, Condition>,
    kind: ConditionKind,
}

impl<'a> Iterator for KindMatches<'a> {
    type Item = &'a Condition;

    fn next(&mut self) -> Option<Self::Item> {
        self.inner.by_ref().find(|c| c.kind == self.kind)
    }
}

impl ConditionSliceExt for [Condition] {
    fn iter_kind(&self, kind: ConditionKind) -> KindMatches<'_> {
        KindMatches {
            inner: self.iter(),
            kind,
        }
    }
}

/// Generic slice-level substrate testkit — pins the FOUR composition
/// laws that bind the [`ConditionSliceExt`] refinement algebra
/// (`iter_kind` → `find_kind` → `has_kind` → `count_kind`) at ONE
/// call site per authored arrangement, sweeping [`ConditionKind::ALL`].
///
/// The [`ConditionSliceExt`] trait publishes four refinements on the
/// slice-level presence-probe axis:
///
/// | refinement | return type | default body                        |
/// |------------|-------------|-------------------------------------|
/// | `iter_kind`| [`KindMatches`]      | (widened primitive, required)      |
/// | `find_kind`| `Option<&Condition>` | `self.iter_kind(k).next()`         |
/// | `has_kind` | `bool`               | `self.find_kind(k).is_some()`      |
/// | `count_kind`| `usize`             | `self.iter_kind(k).count()`        |
///
/// The three coarser refinements are typed projections of the widened
/// primitive by construction. The composition laws that bind them
/// (and therefore surface any implementor that overrode a default
/// with a divergent walk shape — a stored-length cache that drifted,
/// a `.rev().find(...)` returning trailing-first, a `.step_by(2)`
/// artifact from a copy-paste of `iter_kind`) sweep at ONE typed
/// substrate site through this primitive:
///
/// 1. **`find ↔ iter`**: `find_kind(k) == iter_kind(k).next()` — the
///    first-match probe equals the widened stream's first yield.
/// 2. **`count ↔ iter`**: `count_kind(k) == iter_kind(k).count()` —
///    the cardinality probe equals the widened stream's yield count.
/// 3. **`has ↔ find`**: `has_kind(k) == find_kind(k).is_some()` —
///    the presence bit equals the first-match probe's `is_some()`.
/// 4. **`has ↔ count`**: `has_kind(k) == (count_kind(k) > 0)` — the
///    presence bit equals the cardinality's positivity test (the
///    dual composition path from `has` back to the widened primitive
///    that doesn't go through `find`).
///
/// Pre-lift each composition law lived at its own hand-authored
/// nested-`for` loop test in [`tatara_process::boundary`] tests
/// (`condition_slice_find_kind_equals_iter_kind_next`,
/// `condition_slice_count_kind_equals_iter_kind_count`,
/// `condition_slice_has_kind_equals_find_kind_is_some`,
/// `condition_slice_has_and_find_equal_count_greater_than_zero`) —
/// four sibling test bodies whose only per-law knobs were the
/// projection functions being bridged. Post-lift each authored
/// arrangement (empty, single-element, dual-populated, duplicate-
/// populated) pins ALL FOUR laws through ONE
/// `assert_slice_refinement_composition_laws(slice)` call whose body
/// is the substrate primitive's own sweep.
///
/// The primitive binds `<S: ConditionSliceExt + ?Sized>` so both a
/// bare `&[Condition]` and any future implementor of the trait
/// (a wrapper type with additional invariants, an alternative slice
/// projection over a builder's staging Vec) picks up the four-law
/// composition contract through ONE call site. `?Sized` lets the
/// caller pass `slice.as_slice()` or `&owned[..]` without an
/// intermediate reference dance.
///
/// # Compounding
///
/// A FIFTH refinement added to [`ConditionSliceExt`] (a hypothetical
/// `nth_kind(k, n) -> Option<&Condition>` for indexed match access,
/// a `distinct_kinds()` aggregate that returns which kinds appear at
/// least once, a `has_kind_matching(pred)` closure-based predicate
/// probe) lands its composition-law pins as ONE new arm inside this
/// primitive's sweep body. Every downstream test that already reaches
/// this primitive picks up the fifth-refinement pin mechanically —
/// no per-arrangement author-time enumeration of the new law across
/// the four sibling composition-law sites, no re-authored `for kind
/// in ConditionKind::ALL { … }` sweep at every consumer.
///
/// Symmetrical shape to
/// [`crate::tagged_union::assert_find_agrees_with_has`] on the
/// tagged-union parent axis: both project a widened-refinement /
/// coarser-refinement composition law contract onto ONE typed
/// substrate call site, both bind `<T: /* refinement carrier */>`
/// generically, both sweep the addressed closed set
/// ([`ConditionKind::ALL`] here, `<T::Kind as ClosedSet>::ALL`
/// there). The two primitives close the "refinement axis composes"
/// invariant at two adjacent typescape sites — one per closed-set-
/// addressed slice-level refinement, one per closed-set-addressed
/// tagged-union parent-level refinement.
///
/// Theory anchor: THEORY.md §II.1 invariant 5 — composition preserves
/// proofs. The four coarser refinements are typed projections of the
/// widened primitive, and this substrate primitive turns each
/// projection's composition law from doc-prose into a first-class
/// typed theorem provable generically over any
/// `S: ConditionSliceExt + ?Sized`. THEORY.md §VI.1 — generation over
/// composition; a new [`ConditionKind`] variant added to `ALL` reaches
/// every downstream composition-law consumer through the SAME
/// closed-set sweep with no per-caller edit.
#[track_caller]
pub fn assert_slice_refinement_composition_laws<S>(slice: &S)
where
    S: ConditionSliceExt + ?Sized,
{
    let distinct = slice.distinct_kinds();
    for kind in ConditionKind::ALL {
        let find_result = slice.find_kind(kind);
        let has_result = slice.has_kind(kind);
        let count_result = slice.count_kind(kind);
        let iter_next_kind = slice.iter_kind(kind).next().map(|c| c.kind);
        let iter_count = slice.iter_kind(kind).count();

        // find ↔ iter
        assert_eq!(
            find_result.map(|c| c.kind),
            iter_next_kind,
            "find_kind({kind:?}) drifted from iter_kind({kind:?}).next()",
        );
        // count ↔ iter
        assert_eq!(
            count_result, iter_count,
            "count_kind({kind:?}) drifted from iter_kind({kind:?}).count()",
        );
        // has ↔ find
        assert_eq!(
            has_result,
            find_result.is_some(),
            "has_kind({kind:?}) drifted from find_kind({kind:?}).is_some()",
        );
        // has ↔ count
        assert_eq!(
            has_result,
            count_result > 0,
            "has_kind({kind:?}) drifted from (count_kind({kind:?}) > 0)",
        );
        // distinct ↔ has (per-kind membership on the closed-set-inversion axis)
        assert_eq!(
            distinct.contains(&kind),
            has_result,
            "distinct_kinds().contains({kind:?}) drifted from has_kind({kind:?})",
        );

        // has_multiple_of_kind ↔ (count_kind >= 2) — the Boolean
        // cardinality many-arm projection on the per-kind count axis.
        // Peer of `has ↔ (count > 0)` above under the {=0, ≥1, ≥2}
        // per-kind count trichotomy; the per-kind many-arm sits at the
        // ≥ 2 arm. A regression that dropped the second-match short-
        // circuit (returning any ≥ 1 arm), swapped the sides, or
        // conflated with the whole-slice `has_multiple_distinct_kinds`
        // (one axis over) surfaces HERE at the substrate boundary, not
        // as silent drift at every downstream `has-multiple-of-<kind>`
        // require-tag classifier or fleet-wide duplicate-condition
        // audit callsite. Byte-for-byte peer of
        // `has_multiple_distinct_kinds ↔ (distinct_kind_count >= 2)`
        // one axis over under the SAME two-step short-circuit walk
        // shape via the per-kind iterator instead of the distinct
        // iterator.
        let via_iter_multi_kind = {
            let mut it = slice.iter_kind(kind);
            it.next().is_some() && it.next().is_some()
        };
        assert_eq!(
            slice.has_multiple_of_kind(kind),
            count_result >= 2,
            "has_multiple_of_kind({kind:?}) drifted from (count_kind({kind:?}) >= 2)",
        );
        assert_eq!(
            slice.has_multiple_of_kind(kind),
            iter_count >= 2,
            "has_multiple_of_kind({kind:?}) drifted from (iter_kind({kind:?}).count() >= 2)",
        );
        assert_eq!(
            slice.has_multiple_of_kind(kind),
            via_iter_multi_kind,
            "has_multiple_of_kind({kind:?}) drifted from iter_kind({kind:?}) two-step short-circuit",
        );

        // has_unique_of_kind ↔ (count_kind == 1) — the Boolean
        // cardinality mid-endpoint projection on the per-kind count
        // axis. Middle arm of the {=0, =1, ≥2} per-kind count
        // trichotomy alongside `lacks_kind` (=0) and
        // `has_multiple_of_kind` (≥2); the three Booleans partition
        // every non-negative multiplicity — EXACTLY ONE fires on any
        // given `(slice, kind)` pair. A regression that dropped the
        // second-match short-circuit (returning any ≥ 1 arm as
        // `true`), inverted the second-hit predicate (returning `true`
        // on `≥ 2` matches), or conflated with `has_unique_populated_kind`
        // (one struct layer up on the tagged-union parent axis)
        // surfaces HERE at the substrate boundary, not as silent drift
        // at every downstream `has-unique-of-<kind>` require-tag
        // classifier or fleet-wide singleton-condition audit callsite.
        // Byte-for-byte peer of `has_multiple_of_kind ↔ (count_kind
        // >= 2)` above under the SAME two-step short-circuit walk
        // shape via the per-kind iterator.
        let via_iter_unique_kind = {
            let mut it = slice.iter_kind(kind);
            it.next().is_some() && it.next().is_none()
        };
        assert_eq!(
            slice.has_unique_of_kind(kind),
            count_result == 1,
            "has_unique_of_kind({kind:?}) drifted from (count_kind({kind:?}) == 1)",
        );
        assert_eq!(
            slice.has_unique_of_kind(kind),
            iter_count == 1,
            "has_unique_of_kind({kind:?}) drifted from (iter_kind({kind:?}).count() == 1)",
        );
        assert_eq!(
            slice.has_unique_of_kind(kind),
            via_iter_unique_kind,
            "has_unique_of_kind({kind:?}) drifted from iter_kind({kind:?}) two-step short-circuit",
        );

        // unique_of_kind ↔ has_unique_of_kind — the Option<&Condition>
        // witnessing refinement of the Boolean mid-endpoint. Three
        // composition laws bind the witness to its siblings:
        //   (1) has_unique_of_kind(k) == unique_of_kind(k).is_some()
        //   (2) unique_of_kind(k).map(|c| c.kind) == Some(k) iff
        //       has_unique_of_kind(k) else None (the witness carries
        //       the queried kind by construction)
        //   (3) unique_of_kind(k) points at the SAME &Condition
        //       find_kind(k) returned on the singleton arm (both
        //       yield the earliest — and only — match)
        // A regression that dropped the second-match short-circuit
        // (returning `Some(first)` on any `≥ 1` arm), inverted the
        // second-hit predicate (returning `None` on the singleton
        // arm), or returned a non-matching `&Condition` (swapped
        // slots on the two-slice chain lift) surfaces HERE at the
        // substrate boundary rather than as silent drift at every
        // downstream witness callsite. Byte-for-byte peer of
        // `has_unique_of_kind ↔ iter_kind two-step short-circuit` above
        // under the SAME two-step short-circuit walk shape — this arm
        // additionally pins the yielded `&Condition` identity, which
        // the Boolean projection loses.
        let unique_result = slice.unique_of_kind(kind);
        assert_eq!(
            unique_result.is_some(),
            slice.has_unique_of_kind(kind),
            "unique_of_kind({kind:?}).is_some() drifted from has_unique_of_kind({kind:?})",
        );
        assert_eq!(
            unique_result.map(|c| c.kind),
            if slice.has_unique_of_kind(kind) {
                Some(kind)
            } else {
                None
            },
            "unique_of_kind({kind:?}).map(|c| c.kind) must yield Some({kind:?}) iff \
             has_unique_of_kind, else None",
        );
        // Pointer-identity witness — the singleton match returned by
        // `unique_of_kind` is the same allocation `find_kind` yields.
        assert_eq!(
            unique_result.map(|c| c as *const Condition),
            if slice.has_unique_of_kind(kind) {
                find_result.map(|c| c as *const Condition)
            } else {
                None
            },
            "unique_of_kind({kind:?}) must point at the same &Condition as \
             find_kind({kind:?}) on the singleton arm",
        );

        // Trichotomy partition pin — EXACTLY ONE of {lacks_kind,
        // has_unique_of_kind, has_multiple_of_kind} fires on any
        // (slice, kind) pair. A regression that broke exclusivity
        // (two arms fire simultaneously on some kind) or coverage
        // (no arm fires on some kind) surfaces HERE, not as silent
        // drift at every downstream three-arm classifier callsite.
        let arms_true = [
            slice.lacks_kind(kind),
            slice.has_unique_of_kind(kind),
            slice.has_multiple_of_kind(kind),
        ]
        .into_iter()
        .filter(|&b| b)
        .count();
        assert_eq!(
            arms_true, 1,
            "per-kind count trichotomy {{lacks_kind, has_unique_of_kind, has_multiple_of_kind}} \
             must have EXACTLY one arm true for {kind:?}, got {arms_true}",
        );
    }

    // distinct ↔ ALL-filter (canonical subsequence — closed-set-inversion
    // walks ConditionKind::ALL in order, filters by has_kind, dedups by
    // construction). A regression that (a) returned duplicates (a naive
    // `.iter().map(|c| c.kind).collect()` override that skipped dedup),
    // (b) drifted the walk order from ConditionKind::ALL to slice-encounter
    // order, or (c) returned a superset containing absent kinds surfaces
    // HERE at the substrate boundary.
    let canonical: Vec<ConditionKind> = ConditionKind::ALL
        .into_iter()
        .filter(|k| slice.has_kind(*k))
        .collect();
    assert_eq!(
        distinct, canonical,
        "distinct_kinds() must yield ConditionKind::ALL-ordered subsequence of kinds where has_kind is true (no duplicates, canonical order)",
    );

    // iter_distinct_kinds ↔ distinct_kinds — the load-bearing iterator
    // peer of the closed-set-inversion widened primitive. `distinct_kinds`'s
    // default body IS `self.iter_distinct_kinds().collect()`, so the
    // composition law `distinct_kinds() ==
    // iter_distinct_kinds().collect::<Vec<_>>()` holds by construction —
    // a regression that overrode either surface with a divergent walk
    // (short-circuit skipping a kind, drifting the walk order from
    // ConditionKind::ALL, forgetting the `has_kind` filter, or divergent
    // yield sequences between repeated invocations) surfaces HERE at the
    // substrate boundary, not as silent skew between the iter-based fold
    // callsite and the Vec-based callsite. Symmetrical to the tagged-union
    // parent-level substrate testkit
    // `assert_iter_populated_kinds_matches_populated_kinds` under a
    // POSITIVE point-probe.
    let via_iter_distinct: Vec<ConditionKind> = slice.iter_distinct_kinds().collect();
    assert_eq!(
        via_iter_distinct, distinct,
        "iter_distinct_kinds().collect::<Vec<_>>() drifted from distinct_kinds()",
    );
    let via_iter_distinct_again: Vec<ConditionKind> = slice.iter_distinct_kinds().collect();
    assert_eq!(
        via_iter_distinct, via_iter_distinct_again,
        "iter_distinct_kinds() must be pure over &self — repeated collect diverged",
    );

    // distinct_kind_count ↔ distinct_kinds.len() — the scalar
    // cardinality projection of the closed-set-inversion widened
    // primitive. A regression that overrode `distinct_kind_count` to
    // skip a kind, double-count a slot, or drift the walk from
    // `ConditionKind::ALL` surfaces HERE at the substrate boundary,
    // not as silent drift at every downstream `distinct-count-<n>`
    // require-tag classifier or audit-dump callsite.
    assert_eq!(
        slice.distinct_kind_count(),
        distinct.len(),
        "distinct_kind_count() drifted from distinct_kinds().len()",
    );

    // missing ↔ has (per-kind complement on the closed-set-inversion
    // axis). Byte-for-byte peer to the `distinct ↔ has` arm above: the
    // present-side widened primitive `distinct_kinds` binds to
    // `has_kind` via `contains(&k) == has_kind(k)`; the missing-side
    // widened primitive `missing_kinds` binds via
    // `contains(&k) == !has_kind(k)` — the SAME point-probe primitive
    // reached under a negated predicate. A regression that overrode
    // `missing_kinds` to omit the negation (returning `distinct_kinds`
    // instead), inverted the wrong side, or dropped a variant surfaces
    // HERE.
    let missing = slice.missing_kinds();
    for kind in ConditionKind::ALL {
        assert_eq!(
            missing.contains(&kind),
            !slice.has_kind(kind),
            "missing_kinds().contains({kind:?}) drifted from !has_kind({kind:?})",
        );
    }

    // missing ↔ ALL-filter (canonical subsequence — closed-set
    // complement walks ConditionKind::ALL in order, filters by
    // !has_kind, dedups by construction). Peer to the `distinct ↔
    // ALL-filter` arm above; catches ordering + dedup drift on the
    // complement side that the per-kind membership arm cannot detect
    // on its own.
    let canonical_missing: Vec<ConditionKind> = ConditionKind::ALL
        .into_iter()
        .filter(|k| !slice.has_kind(*k))
        .collect();
    assert_eq!(
        missing, canonical_missing,
        "missing_kinds() must yield ConditionKind::ALL-ordered subsequence of kinds where has_kind is false (no duplicates, canonical order)",
    );

    // iter_missing_kinds ↔ missing_kinds — the load-bearing iterator peer
    // of the closed-set-complement widened primitive on the missing side.
    // `missing_kinds`'s default body IS `self.iter_missing_kinds().collect()`,
    // so the composition law
    // `missing_kinds() == iter_missing_kinds().collect::<Vec<_>>()` holds by
    // construction. Byte-for-byte peer of the `iter_distinct_kinds ↔
    // distinct_kinds` arm above under a NEGATED point-probe: a regression
    // that dropped the negation (returning `iter_distinct_kinds`), skipped
    // a kind on the complement side, or drifted the walk from
    // `ConditionKind::ALL` surfaces HERE at the substrate boundary.
    // Symmetrical to the tagged-union parent-level substrate testkit
    // `assert_iter_missing_kinds_matches_missing_kinds` under a NEGATED
    // point-probe.
    let via_iter_missing: Vec<ConditionKind> = slice.iter_missing_kinds().collect();
    assert_eq!(
        via_iter_missing, missing,
        "iter_missing_kinds().collect::<Vec<_>>() drifted from missing_kinds()",
    );
    let via_iter_missing_again: Vec<ConditionKind> = slice.iter_missing_kinds().collect();
    assert_eq!(
        via_iter_missing, via_iter_missing_again,
        "iter_missing_kinds() must be pure over &self — repeated collect diverged",
    );

    // (distinct, missing) partition ConditionKind::ALL — three peer
    // laws that bind the closed-set-inversion widened primitive
    // `distinct_kinds` to its complement peer `missing_kinds`:
    //
    // 1. Disjoint: every kind appears in AT MOST one of the two sets.
    // 2. Covering: every kind appears in AT LEAST one of the two sets
    //    (equivalent to the union covering ConditionKind::ALL).
    // 3. Cardinality partition: `distinct.len() + missing.len() ==
    //    ConditionKind::ALL.len()` — the scalar consequence of (1) +
    //    (2) that a caller reaching for the cardinality peer would
    //    otherwise pay for the two allocations at every callsite.
    for kind in ConditionKind::ALL {
        assert!(
            !(distinct.contains(&kind) && missing.contains(&kind)),
            "(distinct_kinds, missing_kinds) partition invariant violated — both contain {kind:?}",
        );
        assert!(
            distinct.contains(&kind) || missing.contains(&kind),
            "(distinct_kinds, missing_kinds) partition invariant violated — neither contains {kind:?}",
        );
    }
    assert_eq!(
        distinct.len() + missing.len(),
        ConditionKind::ALL.len(),
        "(distinct_kinds, missing_kinds) cardinality partition drift — sum {} ≠ ConditionKind::ALL.len() {}",
        distinct.len() + missing.len(),
        ConditionKind::ALL.len(),
    );

    // missing_kind_count ↔ missing_kinds.len() — the scalar cardinality
    // projection of the closed-set-complement widened primitive. A
    // regression that overrode `missing_kind_count` to drop the
    // negation (returning `distinct_kind_count`), skip a kind, double-
    // count a slot, or drift the walk from `ConditionKind::ALL`
    // surfaces HERE at the substrate boundary, not as silent drift at
    // every downstream `condition-kinds-missing-<n>` require-tag
    // classifier or gap-analysis-dashboard callsite.
    assert_eq!(
        slice.missing_kind_count(),
        missing.len(),
        "missing_kind_count() drifted from missing_kinds().len()",
    );

    // (distinct_kind_count, missing_kind_count) partition
    // ConditionKind::ALL's cardinality — the scalar consequence of the
    // widened-primitive partition law `distinct ∪ missing == ALL,
    // disjoint` above. A regression that (a) drifted the scalar
    // cardinality peer from the widened primitive on either side or
    // (b) drifted the partition invariant surfaces HERE at ONE typed
    // arm rather than as silent drift at every scalar-cardinality
    // callsite that reaches for the sum.
    assert_eq!(
        slice.distinct_kind_count() + slice.missing_kind_count(),
        ConditionKind::ALL.len(),
        "(distinct_kind_count, missing_kind_count) scalar partition drift — sum {} ≠ ConditionKind::ALL.len() {}",
        slice.distinct_kind_count() + slice.missing_kind_count(),
        ConditionKind::ALL.len(),
    );

    // first_distinct_kind ↔ distinct_kinds.first().copied() — the
    // earliest-element scalar projection of the closed-set-inversion
    // widened primitive. Peer of `distinct_kind_count ↔ distinct_kinds
    // .len()` on the scalar-projection axis: where the cardinality peer
    // collapses the SET to its length, the earliest-element peer
    // collapses the SET to its first element. A regression that
    // overrode `first_distinct_kind` to skip a kind, drift the walk
    // from ConditionKind::ALL, forget the short-circuit (returning
    // the LAST hit), or diverge from the widened primitive's canonical
    // ordering surfaces HERE at the substrate boundary, not as silent
    // drift at every downstream `first-distinct-<kind>` require-tag
    // classifier callsite.
    assert_eq!(
        slice.first_distinct_kind(),
        distinct.first().copied(),
        "first_distinct_kind() drifted from distinct_kinds().first().copied()",
    );

    // first_missing_kind ↔ missing_kinds.first().copied() — the
    // earliest-element scalar projection of the closed-set-complement
    // widened primitive. Byte-for-byte peer of `first_distinct_kind`
    // one axis over under a negated predicate: where
    // `first_distinct_kind` scalar-projects the closed-set-INVERSION
    // widened primitive onto its earliest element, this arm scalar-
    // projects the closed-set-COMPLEMENT widened primitive onto its
    // earliest element. A regression that overrode `first_missing_kind`
    // to drop the negation (returning `first_distinct_kind`), skip a
    // kind, drift the walk from ConditionKind::ALL, or forget the
    // short-circuit (returning the LAST missing hit) surfaces HERE at
    // the substrate boundary, not as silent drift at every downstream
    // `first-missing-<kind>` require-tag classifier callsite.
    assert_eq!(
        slice.first_missing_kind(),
        missing.first().copied(),
        "first_missing_kind() drifted from missing_kinds().first().copied()",
    );

    // last_distinct_kind ↔ distinct_kinds.last().copied() — the
    // latest-element scalar projection of the closed-set-inversion
    // widened primitive. Time-reversed peer of `first_distinct_kind
    // ↔ distinct_kinds.first().copied()` under the SAME `has_kind`
    // predicate but with the closed-set walk reversed: where the
    // earliest-element peer picks the smallest ALL index that hits,
    // this arm picks the LARGEST. A regression that overrode
    // `last_distinct_kind` to skip a kind, drift the walk direction
    // (returning `first_distinct_kind`), forget the short-circuit
    // (returning `distinct_kinds().rev().next()` allocation), or
    // diverge from the widened primitive's canonical ordering
    // surfaces HERE at the substrate boundary, not as silent drift
    // at every downstream `last-distinct-<kind>` require-tag
    // classifier callsite.
    assert_eq!(
        slice.last_distinct_kind(),
        distinct.last().copied(),
        "last_distinct_kind() drifted from distinct_kinds().last().copied()",
    );

    // last_missing_kind ↔ missing_kinds.last().copied() — the
    // latest-element scalar projection of the closed-set-complement
    // widened primitive. Byte-for-byte peer of `last_distinct_kind`
    // one axis over under a NEGATED predicate: where
    // `last_distinct_kind` scalar-projects the closed-set-INVERSION
    // widened primitive onto its LATEST element, this arm scalar-
    // projects the closed-set-COMPLEMENT widened primitive onto its
    // LATEST element. A regression that overrode `last_missing_kind`
    // to drop the negation (returning `last_distinct_kind`), reverse
    // the walk direction (returning `first_missing_kind`), skip a
    // kind, or forget the short-circuit surfaces HERE at the
    // substrate boundary, not as silent drift at every downstream
    // `last-missing-<kind>` require-tag classifier callsite.
    assert_eq!(
        slice.last_missing_kind(),
        missing.last().copied(),
        "last_missing_kind() drifted from missing_kinds().last().copied()",
    );

    // is_kind_saturated ↔ (missing_kind_count == 0) — the Boolean
    // saturation-endpoint projection of the closed-set-complement
    // scalar cardinality. Peer of `first_missing_kind ↔ missing_kinds
    // .first().copied()` on the endpoint-projection axis: where the
    // earliest-element peer collapses the missing SET to its first
    // element, this Boolean peer collapses the missing scalar to its
    // zero-arm test. A regression that overrode `is_kind_saturated` to
    // drop the negation (returning `slice.is_empty()`), skip a kind,
    // or drift the walk from `ConditionKind::ALL` surfaces HERE at
    // the substrate boundary, not as silent drift at every downstream
    // `is-kind-saturated` require-tag classifier or fleet-wide gap-
    // analysis dashboard callsite. Byte-for-byte peer of
    // `crate::tagged_union::TaggedUnion::is_saturated` one struct-
    // layer up under the same `<CLOSED_SET>::ALL.iter().all(has)`
    // short-circuit shape.
    assert_eq!(
        slice.is_kind_saturated(),
        slice.missing_kind_count() == 0,
        "is_kind_saturated() drifted from (missing_kind_count() == 0)",
    );
    assert_eq!(
        slice.is_kind_saturated(),
        missing.is_empty(),
        "is_kind_saturated() drifted from missing_kinds().is_empty()",
    );

    // is_kind_empty ↔ (distinct_kind_count == 0) — the Boolean cardinality
    // zero-endpoint projection of the closed-set-inversion scalar
    // cardinality. Axis-parity mirror of `is_kind_saturated ↔
    // (missing_kind_count == 0)` on the closed-set-inversion axis: where
    // the saturation-endpoint peer collapses the missing scalar to its
    // zero-arm test, this zero-endpoint peer collapses the distinct
    // scalar to its zero-arm test. Together the two Booleans name the
    // (empty, saturated) endpoints of the (distinct, missing)
    // partition — on any `N ≥ 1` closed set at most ONE of
    // `is_kind_empty()` and `is_kind_saturated()` returns `true`; on the
    // `N == 0` closed set both return `true` vacuously. Also pins the
    // definitional negation `is_kind_empty() == !has_any_distinct_kind()`
    // binding this zero-endpoint Boolean projection to the at-least-one
    // halfspace peer on the SAME distinct axis. A regression that
    // overrode `is_kind_empty` to drop the negation (returning
    // `has_any_distinct_kind`), swap the wrong side (returning
    // `is_kind_saturated`), skip a kind, or drift the walk from
    // `ConditionKind::ALL` surfaces HERE at the substrate boundary, not
    // as silent drift at every downstream `is-kind-empty` require-tag
    // classifier or fleet-wide empty-coverage dashboard callsite. Byte-
    // for-byte peer of `crate::tagged_union::TaggedUnion::is_empty` one
    // struct-layer up under the SAME zero-endpoint short-circuit shape.
    assert_eq!(
        slice.is_kind_empty(),
        slice.distinct_kind_count() == 0,
        "is_kind_empty() drifted from (distinct_kind_count() == 0)",
    );
    assert_eq!(
        slice.is_kind_empty(),
        distinct.is_empty(),
        "is_kind_empty() drifted from distinct_kinds().is_empty()",
    );
    assert_eq!(
        slice.is_kind_empty(),
        !slice.has_any_distinct_kind(),
        "is_kind_empty() drifted from !has_any_distinct_kind()",
    );
    assert_eq!(
        slice.is_kind_empty(),
        slice.iter_distinct_kinds().next().is_none(),
        "is_kind_empty() drifted from iter_distinct_kinds().next().is_none()",
    );
    assert_eq!(
        slice.is_kind_empty(),
        slice.first_distinct_kind().is_none(),
        "is_kind_empty() drifted from first_distinct_kind().is_none()",
    );

    // is_kind_partially_covered ↔ !is_kind_empty && !is_kind_saturated —
    // the Boolean cardinality parent-state middle-arm projection on the
    // closed-set partition. Third and final arm of the trichotomy
    // (empty, partially covered, saturated) at the slice level,
    // closing the natural partition alongside `is_kind_empty` (=0
    // zero-endpoint on the distinct axis) and `is_kind_saturated`
    // (=0 zero-endpoint on the missing axis). Together the three
    // Booleans partition the (distinct_kind_count, missing_kind_count)
    // product at (0, N), (open, open), and (N, 0) respectively — on
    // any `N ≥ 1` closed set at most ONE returns `true`; the vacuous
    // `N == 0` case is impossible here because `ConditionKind::ALL`
    // carries ≥ 1 variant by construction. A regression that
    // overrode `is_kind_partially_covered` to drop one bit of the
    // fused walk (returning `has_any_distinct_kind` — TOO LOOSE,
    // admits saturated slices as partial), forget the pair short-
    // circuit (returning a scalar comparison
    // `distinct_kind_count > 0 && distinct_kind_count < ALL.len()`
    // that walks every slot), or swap the wrong side (returning
    // `is_kind_empty || is_kind_saturated` — the negation of the
    // middle-arm on any `N ≥ 1` closed set) surfaces HERE at the
    // substrate boundary, not as silent drift at every downstream
    // `is-kind-partially-covered` require-tag classifier or mixed-
    // coverage diagnostic callsite. Byte-for-byte peer of
    // `crate::tagged_union::TaggedUnion::is_partially_populated` one
    // struct-layer up under the SAME fused short-circuit walk shape,
    // and byte-for-byte peer of the trichotomy partition law
    // `is_empty + is_partially_populated + is_saturated == 1`
    // pinned one struct-layer up by
    // `crate::tagged_union::assert_is_partially_populated_matches_cardinality`.
    // Also pins the paired-halfspace composition
    // `is_kind_partially_covered() == has_any_distinct_kind() &&
    // has_any_missing_kind()` and the paired-scalar composition
    // `is_kind_partially_covered() == (distinct_kind_count() > 0 &&
    // missing_kind_count() > 0)` binding this Boolean projection to the
    // at-least-one halfspace + scalar peers on BOTH axes.
    assert_eq!(
        slice.is_kind_partially_covered(),
        !slice.is_kind_empty() && !slice.is_kind_saturated(),
        "is_kind_partially_covered() drifted from (!is_kind_empty() && !is_kind_saturated())",
    );
    assert_eq!(
        slice.is_kind_partially_covered(),
        slice.has_any_distinct_kind() && slice.has_any_missing_kind(),
        "is_kind_partially_covered() drifted from (has_any_distinct_kind() && has_any_missing_kind())",
    );
    assert_eq!(
        slice.is_kind_partially_covered(),
        slice.distinct_kind_count() > 0 && slice.missing_kind_count() > 0,
        "is_kind_partially_covered() drifted from (distinct_kind_count() > 0 && missing_kind_count() > 0)",
    );
    // Trichotomy partition law — EXACTLY ONE of
    // `is_kind_empty`, `is_kind_partially_covered`, `is_kind_saturated`
    // returns `true` on any `N ≥ 1` closed set. Byte-for-byte peer of
    // `is_empty + is_partially_populated + is_saturated == 1` one
    // struct-layer up.
    assert_eq!(
        usize::from(slice.is_kind_empty())
            + usize::from(slice.is_kind_partially_covered())
            + usize::from(slice.is_kind_saturated()),
        1,
        "trichotomy partition law violated — is_kind_empty + is_kind_partially_covered + is_kind_saturated must equal 1 (got {} + {} + {} = {})",
        usize::from(slice.is_kind_empty()),
        usize::from(slice.is_kind_partially_covered()),
        usize::from(slice.is_kind_saturated()),
        usize::from(slice.is_kind_empty())
            + usize::from(slice.is_kind_partially_covered())
            + usize::from(slice.is_kind_saturated()),
    );

    // has_any_missing_kind ↔ !is_kind_saturated — the Boolean at-
    // least-one halfspace projection of the closed-set-complement
    // scalar cardinality. Peer of `is_kind_saturated ↔
    // (missing_kind_count == 0)` on the Boolean-negation axis: where
    // the saturation-endpoint peer tests the zero-arm, this at-least-
    // one halfspace peer tests its negation. Together the two Booleans
    // partition the missing-cardinality closed set — exactly one is
    // `true` for every slice. A regression that overrode
    // `has_any_missing_kind` to drop the negation (returning
    // `is_kind_saturated`), skip a kind, or drift the walk from
    // `ConditionKind::ALL` surfaces HERE at the substrate boundary,
    // not as silent drift at every downstream `has-any-missing-kind`
    // require-tag classifier or fleet-wide gap-analysis dashboard
    // callsite. Byte-for-byte peer of
    // `crate::tagged_union::TaggedUnion::has_any_missing_kind` one
    // struct-layer up under the SAME `!is_saturated` definitional
    // negation shape. Also pins the widened composition laws
    // `has_any_missing_kind() == (missing_kind_count() > 0)` and
    // `has_any_missing_kind() == !missing_kinds().is_empty()` at every
    // slice — binds the at-least-one halfspace Boolean projection to
    // the widened + scalar closed-set-complement primitives without
    // paying for the Vec allocation.
    assert_eq!(
        slice.has_any_missing_kind(),
        !slice.is_kind_saturated(),
        "has_any_missing_kind() drifted from !is_kind_saturated()",
    );
    assert_eq!(
        slice.has_any_missing_kind(),
        slice.missing_kind_count() > 0,
        "has_any_missing_kind() drifted from (missing_kind_count() > 0)",
    );
    assert_eq!(
        slice.has_any_missing_kind(),
        !missing.is_empty(),
        "has_any_missing_kind() drifted from !missing_kinds().is_empty()",
    );

    // has_any_distinct_kind ↔ (distinct_kind_count > 0) — the Boolean
    // at-least-one halfspace projection of the closed-set-inversion
    // scalar cardinality. Peer of `has_any_missing_kind ↔
    // !is_kind_saturated` on the axis-parity axis: where the at-least-
    // one halfspace peer on the closed-set-complement axis tests the
    // ≥ 1 arm on the missing scalar, this at-least-one halfspace peer
    // on the closed-set-inversion axis tests the ≥ 1 arm on the
    // distinct scalar. A regression that overrode `has_any_distinct_kind`
    // to drop the short-circuit, skip a kind, or drift the walk from
    // `ConditionKind::ALL` surfaces HERE at the substrate boundary, not
    // as silent drift at every downstream `has-any-distinct-kind`
    // require-tag classifier or fleet-wide coverage-analysis dashboard
    // callsite. Byte-for-byte peer of
    // `crate::tagged_union::TaggedUnion::has_any_populated_kind` one
    // struct-layer up under the SAME `any(has)` short-circuit shape.
    // Also pins the widened composition law `has_any_distinct_kind() ==
    // !distinct_kinds().is_empty()` at every slice — binds the at-
    // least-one halfspace Boolean projection to the widened primitive
    // without paying for the Vec allocation.
    assert_eq!(
        slice.has_any_distinct_kind(),
        slice.distinct_kind_count() > 0,
        "has_any_distinct_kind() drifted from (distinct_kind_count() > 0)",
    );
    assert_eq!(
        slice.has_any_distinct_kind(),
        !distinct.is_empty(),
        "has_any_distinct_kind() drifted from !distinct_kinds().is_empty()",
    );
    assert_eq!(
        slice.has_any_distinct_kind(),
        slice.first_distinct_kind().is_some(),
        "has_any_distinct_kind() drifted from first_distinct_kind().is_some()",
    );

    // has_unique_distinct_kind ↔ (distinct_kind_count == 1) — the
    // Boolean cardinality-mid-endpoint projection of the closed-set-
    // inversion scalar cardinality. Peer of `has_unique_missing_kind
    // ↔ (missing_kind_count == 1)` (=1 mid-endpoint on the missing
    // axis) on the axis-parity axis: where the missing-axis peer
    // tests the exactly-one arm on the missing scalar, this
    // distinct-axis peer tests the exactly-one arm on the distinct
    // scalar. A regression that overrode `has_unique_distinct_kind`
    // to drop the second-slot short-circuit (returning any at-least-
    // one arm), skip a kind, drift the walk from `ConditionKind::ALL`,
    // or conflate with `has_any_distinct_kind` (the ≥ 1 halfspace)
    // surfaces HERE at the substrate boundary, not as silent drift at
    // every downstream `has-unique-distinct-kind` require-tag
    // classifier or singleton-coverage diagnostic callsite. Byte-for-
    // byte peer of `crate::tagged_union::TaggedUnion::has_unique_populated_kind`
    // one struct-layer up under the SAME two-step short-circuit walk
    // shape. Also pins the widened composition law
    // `has_unique_distinct_kind() == (distinct_kinds().len() == 1)`
    // at every slice — binds the cardinality-mid-endpoint Boolean
    // projection to the widened + scalar closed-set-inversion
    // primitives without paying for the Vec allocation on the ≥ 2-
    // distinct arms (where the short-circuit fires).
    assert_eq!(
        slice.has_unique_distinct_kind(),
        slice.distinct_kind_count() == 1,
        "has_unique_distinct_kind() drifted from (distinct_kind_count() == 1)",
    );
    assert_eq!(
        slice.has_unique_distinct_kind(),
        distinct.len() == 1,
        "has_unique_distinct_kind() drifted from (distinct_kinds().len() == 1)",
    );

    // has_multiple_distinct_kinds ↔ (distinct_kind_count >= 2) — the
    // Boolean cardinality many-arm projection of the closed-set-
    // inversion scalar cardinality. Peer of `has_any_distinct_kind ↔
    // !distinct_kinds.is_empty()` (≥ 1 halfspace) and
    // `has_unique_distinct_kind ↔ (distinct_kind_count == 1)` (= 1
    // mid-endpoint) on the Boolean-projection axis: where those peers
    // test the ≥ 1 and = 1 arms on the distinct scalar, this many-arm
    // peer tests the ≥ 2 arm. Together with the empty-endpoint
    // (`!has_any_distinct_kind`) and `has_unique_distinct_kind`, the
    // three Booleans partition the distinct-cardinality closed set at
    // 0, 1, and ≥ 2 respectively — every slice satisfies EXACTLY ONE
    // of the three projections. A regression that overrode
    // `has_multiple_distinct_kinds` to drop the second-slot short-
    // circuit (returning `true` on any ≥ 1-distinct arm), skip a
    // kind, drift the walk from `ConditionKind::ALL`, or conflate
    // with `has_any_distinct_kind` (the ≥ 1 halfspace) surfaces HERE
    // at the substrate boundary, not as silent drift at every
    // downstream `has-multiple-distinct-kinds` require-tag classifier
    // or multi-coverage diagnostic callsite. Byte-for-byte peer of
    // `crate::tagged_union::TaggedUnion::has_multiple_populated_kinds`
    // one struct-layer up under the SAME two-step short-circuit walk
    // shape. Also pins the widened composition law
    // `has_multiple_distinct_kinds() == (distinct_kinds().len() >= 2)`
    // at every slice — binds the cardinality-many-arm Boolean
    // projection to the widened + scalar closed-set-inversion
    // primitives without paying for the Vec allocation on the ≥ 2-
    // distinct arms (where the short-circuit fires) or the full-slot
    // walk on the scalar counter.
    assert_eq!(
        slice.has_multiple_distinct_kinds(),
        slice.distinct_kind_count() >= 2,
        "has_multiple_distinct_kinds() drifted from (distinct_kind_count() >= 2)",
    );
    assert_eq!(
        slice.has_multiple_distinct_kinds(),
        distinct.len() >= 2,
        "has_multiple_distinct_kinds() drifted from (distinct_kinds().len() >= 2)",
    );

    // has_at_most_one_distinct_kind ↔ !has_multiple_distinct_kinds —
    // the Boolean cardinality "≤ 1" negation projection of the many-
    // arm primitive on the closed-set-inversion axis. Peer of
    // `has_multiple_distinct_kinds ↔ (distinct_kind_count >= 2)` (≥ 2
    // many-arm) under the definitional Boolean negation
    // `!(≥ 2) == (≤ 1)`. Together with `!has_any_distinct_kind` (=0
    // empty-endpoint reached via `has_any_distinct_kind`) and
    // `has_unique_distinct_kind` (=1 mid-endpoint), the "≤ 1"
    // primitive collapses to the trichotomy-union
    // `!has_any_distinct_kind() || has_unique_distinct_kind()` — a
    // regression that overrode `has_at_most_one_distinct_kind` to drop
    // the definitional negation (returning `has_multiple_distinct_kinds`
    // itself), swap the wrong side, or drift the walk from the
    // many-arm primitive surfaces HERE at the substrate boundary, not
    // as silent drift at every downstream
    // `has-at-most-one-distinct-kind` require-tag classifier or
    // empty-or-singleton coverage-analysis diagnostic callsite. Byte-
    // for-byte peer of
    // `crate::tagged_union::TaggedUnion::has_at_most_one_populated_kind`
    // one struct-layer up under the SAME `!has_multiple_populated_kinds`
    // definitional negation shape. Axis-parity mirror of the closed-
    // set-complement "≤ 1" negation peer
    // `has_at_most_one_missing_kind ↔ !has_multiple_missing_kinds` at
    // the same slice-level trait. Also pins the widened composition
    // laws
    // `has_at_most_one_distinct_kind() == (distinct_kind_count() <= 1)`
    // and `has_at_most_one_distinct_kind() == (distinct_kinds().len() <= 1)`
    // at every slice — binds the "≤ 1" Boolean projection to the
    // widened + scalar closed-set-inversion primitives without paying
    // for the Vec allocation on the ≤ 1-distinct arms (where the
    // negated short-circuit fires immediately after the many-arm walk
    // stops) or the full-slot walk on the scalar counter. Also pins
    // the trichotomy-union composition law
    // `has_at_most_one_distinct_kind() == !has_any_distinct_kind() ||
    // has_unique_distinct_kind()` at every slice — surfaces any
    // implementor that drifted the trichotomy union operator from
    // `||` to `&&` or that broke one of the two arm primitives while
    // leaving the "≤ 1" negation of the many-arm intact.
    assert_eq!(
        slice.has_at_most_one_distinct_kind(),
        !slice.has_multiple_distinct_kinds(),
        "has_at_most_one_distinct_kind() drifted from !has_multiple_distinct_kinds()",
    );
    assert_eq!(
        slice.has_at_most_one_distinct_kind(),
        slice.distinct_kind_count() <= 1,
        "has_at_most_one_distinct_kind() drifted from (distinct_kind_count() <= 1)",
    );
    assert_eq!(
        slice.has_at_most_one_distinct_kind(),
        distinct.len() <= 1,
        "has_at_most_one_distinct_kind() drifted from (distinct_kinds().len() <= 1)",
    );
    assert_eq!(
        slice.has_at_most_one_distinct_kind(),
        !slice.has_any_distinct_kind() || slice.has_unique_distinct_kind(),
        "has_at_most_one_distinct_kind() drifted from (!has_any_distinct_kind() || has_unique_distinct_kind())",
    );

    // has_unique_missing_kind ↔ (missing_kind_count == 1) — the
    // Boolean cardinality-mid-endpoint projection of the closed-set-
    // complement scalar cardinality. Peer of `has_any_missing_kind ↔
    // !is_kind_saturated` on the Boolean-projection axis: where the
    // at-least-one halfspace peer tests the ≥ 1 arm on the missing
    // scalar, this cardinality-mid-endpoint peer tests the exactly-
    // one arm. Together with `is_kind_saturated` (zero-arm) and the
    // future many-arm peer, the three Booleans partition the missing-
    // cardinality closed set at 0, 1, and ≥ 2 respectively. A
    // regression that overrode `has_unique_missing_kind` to drop the
    // second-slot short-circuit (returning any partial-populated
    // arm), skip a kind, drift the walk from `ConditionKind::ALL`, or
    // conflate with `is_kind_saturated` (the zero-arm) surfaces HERE
    // at the substrate boundary, not as silent drift at every
    // downstream `has-unique-missing-kind` require-tag classifier or
    // near-saturation-endpoint diagnostic callsite. Byte-for-byte
    // peer of `crate::tagged_union::TaggedUnion::has_unique_missing_kind`
    // one struct-layer up under the SAME two-step short-circuit
    // walk shape. Also pins the widened composition law
    // `has_unique_missing_kind() == (missing_kinds().len() == 1)` at
    // every slice — binds the cardinality-mid-endpoint Boolean
    // projection to the widened + scalar closed-set-complement
    // primitives without paying for the Vec allocation on the ≥ 2-
    // missing arms (where the short-circuit fires).
    assert_eq!(
        slice.has_unique_missing_kind(),
        slice.missing_kind_count() == 1,
        "has_unique_missing_kind() drifted from (missing_kind_count() == 1)",
    );
    assert_eq!(
        slice.has_unique_missing_kind(),
        missing.len() == 1,
        "has_unique_missing_kind() drifted from (missing_kinds().len() == 1)",
    );

    // has_multiple_missing_kinds ↔ (missing_kind_count >= 2) — the
    // Boolean cardinality many-arm projection of the closed-set-
    // complement scalar cardinality. Peer of `has_any_missing_kind ↔
    // !is_kind_saturated` (≥ 1 halfspace) and `has_unique_missing_kind
    // ↔ (missing_kind_count == 1)` (= 1 mid-endpoint) on the Boolean-
    // projection axis: where those peers test the ≥ 1 and = 1 arms on
    // the missing scalar, this many-arm peer tests the ≥ 2 arm.
    // Together with `is_kind_saturated` (zero-arm) and
    // `has_unique_missing_kind` (one-arm), the three Booleans
    // partition the missing-cardinality closed set at 0, 1, and ≥ 2
    // respectively — every slice satisfies EXACTLY ONE of the three
    // projections. A regression that overrode `has_multiple_missing_kinds`
    // to drop the second-slot short-circuit (returning `true` on any
    // ≥ 1-missing arm), skip a kind, drift the walk from
    // `ConditionKind::ALL`, or conflate with `has_any_missing_kind`
    // (the ≥ 1 halfspace) surfaces HERE at the substrate boundary,
    // not as silent drift at every downstream
    // `has-multiple-missing-kinds` require-tag classifier or
    // coverage-gap diagnostic callsite. Byte-for-byte peer of
    // `crate::tagged_union::TaggedUnion::has_multiple_missing_kinds`
    // one struct-layer up under the SAME two-step short-circuit walk
    // shape. Also pins the widened composition law
    // `has_multiple_missing_kinds() == (missing_kinds().len() >= 2)`
    // at every slice — binds the cardinality-many-arm Boolean
    // projection to the widened + scalar closed-set-complement
    // primitives without paying for the Vec allocation on the ≥ 2-
    // missing arms (where the short-circuit fires) or the full-slot
    // walk on the scalar counter.
    assert_eq!(
        slice.has_multiple_missing_kinds(),
        slice.missing_kind_count() >= 2,
        "has_multiple_missing_kinds() drifted from (missing_kind_count() >= 2)",
    );
    assert_eq!(
        slice.has_multiple_missing_kinds(),
        missing.len() >= 2,
        "has_multiple_missing_kinds() drifted from (missing_kinds().len() >= 2)",
    );

    // has_at_most_one_missing_kind ↔ !has_multiple_missing_kinds — the
    // Boolean cardinality "≤ 1" negation projection of the many-arm
    // primitive on the closed-set-complement axis. Peer of
    // `has_multiple_missing_kinds ↔ (missing_kind_count >= 2)` (≥ 2
    // many-arm) under the definitional Boolean negation
    // `!(≥ 2) == (≤ 1)`. Together with `is_kind_saturated` (=0
    // zero-arm) and `has_unique_missing_kind` (=1 mid-endpoint), the
    // "≤ 1" primitive collapses to the trichotomy-union
    // `is_kind_saturated() || has_unique_missing_kind()` — a
    // regression that overrode `has_at_most_one_missing_kind` to drop
    // the definitional negation (returning `has_multiple_missing_kinds`
    // itself), swap the wrong side, or drift the walk from the
    // many-arm primitive surfaces HERE at the substrate boundary, not
    // as silent drift at every downstream
    // `has-at-most-one-missing-kind` require-tag classifier or near-
    // saturation-or-saturated gap-analysis diagnostic callsite. Byte-
    // for-byte peer of
    // `crate::tagged_union::TaggedUnion::has_at_most_one_missing_kind`
    // one struct-layer up under the SAME `!has_multiple_missing_kinds`
    // definitional negation shape. Also pins the widened composition
    // laws
    // `has_at_most_one_missing_kind() == (missing_kind_count() <= 1)`
    // and `has_at_most_one_missing_kind() == (missing_kinds().len() <= 1)`
    // at every slice — binds the "≤ 1" Boolean projection to the
    // widened + scalar closed-set-complement primitives without paying
    // for the Vec allocation on the ≤ 1-missing arms (where the
    // negated short-circuit fires immediately after the many-arm walk
    // stops) or the full-slot walk on the scalar counter. Also pins
    // the trichotomy-union composition law
    // `has_at_most_one_missing_kind() == is_kind_saturated() ||
    // has_unique_missing_kind()` at every slice — surfaces any
    // implementor that drifted the trichotomy union operator from
    // `||` to `&&` or that broke one of the two arm primitives while
    // leaving the "≤ 1" negation of the many-arm intact.
    assert_eq!(
        slice.has_at_most_one_missing_kind(),
        !slice.has_multiple_missing_kinds(),
        "has_at_most_one_missing_kind() drifted from !has_multiple_missing_kinds()",
    );
    assert_eq!(
        slice.has_at_most_one_missing_kind(),
        slice.missing_kind_count() <= 1,
        "has_at_most_one_missing_kind() drifted from (missing_kind_count() <= 1)",
    );
    assert_eq!(
        slice.has_at_most_one_missing_kind(),
        missing.len() <= 1,
        "has_at_most_one_missing_kind() drifted from (missing_kinds().len() <= 1)",
    );
    assert_eq!(
        slice.has_at_most_one_missing_kind(),
        slice.is_kind_saturated() || slice.has_unique_missing_kind(),
        "has_at_most_one_missing_kind() drifted from (is_kind_saturated() || has_unique_missing_kind())",
    );

    // lacks_kind ↔ !has_kind — the Boolean per-kind complement
    // projection on the closed-set-complement axis. Peer of
    // `is_kind_saturated ↔ (missing_kind_count == 0)` on the Boolean-
    // projection axis: where the saturation-endpoint peer collapses
    // the whole missing scalar to its zero-arm test, this per-kind
    // peer collapses the whole missing SET to its per-kind membership
    // Boolean for ONE addressed kind. A regression that overrode
    // `lacks_kind` to drop the negation (returning `has_kind`), swap
    // the wrong side, or drift the walk from `has_kind` surfaces HERE
    // at the substrate boundary, not as silent drift at every
    // downstream `lacks-<kind>` require-tag classifier or
    // dependency-satisfaction coherence check callsite. Byte-for-byte
    // peer of `crate::tagged_union::TaggedUnion::lacks` one struct-
    // layer up under the SAME `!has(kind)` definitional negation
    // shape. Also pins the widened composition law
    // `lacks_kind(k) == missing_kinds().contains(&k)` at every arm —
    // binds the per-kind Boolean projection to the widened closed-set-
    // complement primitive without paying for the Vec allocation.
    for kind in ConditionKind::ALL {
        assert_eq!(
            slice.lacks_kind(kind),
            !slice.has_kind(kind),
            "lacks_kind({kind:?}) drifted from !has_kind({kind:?})",
        );
        assert_eq!(
            slice.lacks_kind(kind),
            missing.contains(&kind),
            "lacks_kind({kind:?}) drifted from missing_kinds().contains(&{kind:?})",
        );
    }

    // has_only_kind(k) ↔ (distinct_kinds() == vec![k]) — the kind-
    // scoped strict-refinement projection on the closed-set-inversion
    // axis. Peer of `lacks_kind ↔ !has_kind` under a symmetrical
    // refinement axis: where `lacks_kind` refines `has_kind` under a
    // definitional negation (per-kind Boolean complement),
    // `has_only_kind` refines it under a well-formed-diagonal
    // strengthening (per-kind Boolean AND
    // `distinct_kind_count() == 1`). Together the two peers occupy
    // the (weaken, strengthen) axes of the per-kind projection on the
    // closed-set-inversion widened primitive at the slice level.
    // A regression that overrode `has_only_kind` to drop the fused-
    // walk short-circuit (returning `has_kind` — TOO LOOSE, admits
    // multi-kind slices) or to drop the `saw_kind` arm (returning
    // `distinct_kind_count() <= 1` — TOO LOOSE, admits the empty
    // slice as well-formed) surfaces HERE at the substrate boundary,
    // not as silent drift at every downstream `has-only-<kind>`
    // require-tag classifier or well-formed-diagonal coherence check
    // callsite. Byte-for-byte peer of
    // `crate::tagged_union::TaggedUnion::has_only` one struct-layer
    // up under the SAME fused short-circuit closed-set walk shape.
    // Also pins the widened composition laws
    // `has_only_kind(k) == (distinct_kinds() == vec![k])`,
    // `has_only_kind(k) == (has_kind(k) && distinct_kind_count() == 1)`,
    // and the kind-domain exhaustivity law "AT MOST ONE `k` satisfies
    // `has_only_kind(k)` on any slice".
    let mut has_only_hits = 0usize;
    for kind in ConditionKind::ALL {
        let expected_widened = distinct == vec![kind];
        assert_eq!(
            slice.has_only_kind(kind),
            expected_widened,
            "has_only_kind({kind:?}) drifted from (distinct_kinds() == vec![{kind:?}])",
        );
        assert_eq!(
            slice.has_only_kind(kind),
            slice.has_kind(kind) && slice.distinct_kind_count() == 1,
            "has_only_kind({kind:?}) drifted from (has_kind({kind:?}) && distinct_kind_count() == 1)",
        );
        // Strict-refinement of `has_kind`: has_only_kind(k) ⟹ has_kind(k).
        if slice.has_only_kind(kind) {
            assert!(
                slice.has_kind(kind),
                "has_only_kind({kind:?}) implies has_kind({kind:?})",
            );
            has_only_hits += 1;
        }
    }
    // Kind-domain exhaustivity — AT MOST ONE `k` satisfies
    // `has_only_kind(k)` on any slice.
    assert!(
        has_only_hits <= 1,
        "has_only_kind(k) satisfied by more than one kind (count={has_only_hits}) — kind-domain exhaustivity violated",
    );
    // has_only_kind(k) for SOME k ⟺ distinct_kind_count() == 1 — the
    // kind-domain-exhaustivity ⟺ well-formed-diagonal pin.
    assert_eq!(
        has_only_hits == 1,
        slice.distinct_kind_count() == 1,
        "has_only_kind holds for some kind iff distinct_kind_count() == 1",
    );

    // lacks_only_kind(k) ↔ (missing_kinds() == vec![k]) — the kind-
    // scoped strict-refinement projection on the closed-set-complement
    // axis. Byte-for-byte peer of `has_only_kind` under complement:
    // where `has_only_kind` refines `has_kind` under a well-formed-
    // diagonal strengthening on the populated axis, `lacks_only_kind`
    // refines `lacks_kind` under the same strengthening on the missing
    // axis — the closed-set-complement mirror closes the (populated,
    // missing) × (subset, equal) 2x2 kind-scoped strict-refinement grid
    // at the slice level alongside `has_kind` / `lacks_kind` /
    // `has_only_kind`. A regression that overrode `lacks_only_kind` to
    // drop the fused-walk short-circuit (returning `lacks_kind` — TOO
    // LOOSE, admits multi-missing-kind slices) or to drop the
    // `saw_kind` arm (returning `missing_kind_count() <= 1` — TOO
    // LOOSE, admits the saturated slice as well-formed on the missing
    // axis) surfaces HERE at the substrate boundary, not as silent
    // drift at every downstream `lacks-only-<kind>` require-tag
    // classifier or near-saturation-diagonal coherence check callsite.
    // Byte-for-byte peer of `crate::tagged_union::TaggedUnion::lacks_only`
    // one struct-layer up under the SAME fused short-circuit closed-set
    // walk shape. Also pins the widened composition laws
    // `lacks_only_kind(k) == (missing_kinds() == vec![k])`,
    // `lacks_only_kind(k) == (lacks_kind(k) && missing_kind_count() == 1)`,
    // and the kind-domain exhaustivity law "AT MOST ONE `k` satisfies
    // `lacks_only_kind(k)` on any slice".
    let mut lacks_only_hits = 0usize;
    for kind in ConditionKind::ALL {
        let expected_widened = missing == vec![kind];
        assert_eq!(
            slice.lacks_only_kind(kind),
            expected_widened,
            "lacks_only_kind({kind:?}) drifted from (missing_kinds() == vec![{kind:?}])",
        );
        assert_eq!(
            slice.lacks_only_kind(kind),
            slice.lacks_kind(kind) && slice.missing_kind_count() == 1,
            "lacks_only_kind({kind:?}) drifted from (lacks_kind({kind:?}) && missing_kind_count() == 1)",
        );
        // Strict-refinement of `lacks_kind`: lacks_only_kind(k) ⟹ lacks_kind(k).
        if slice.lacks_only_kind(kind) {
            assert!(
                slice.lacks_kind(kind),
                "lacks_only_kind({kind:?}) implies lacks_kind({kind:?})",
            );
            lacks_only_hits += 1;
        }
    }
    // Kind-domain exhaustivity — AT MOST ONE `k` satisfies
    // `lacks_only_kind(k)` on any slice.
    assert!(
        lacks_only_hits <= 1,
        "lacks_only_kind(k) satisfied by more than one kind (count={lacks_only_hits}) — kind-domain exhaustivity violated",
    );
    // lacks_only_kind(k) for SOME k ⟺ missing_kind_count() == 1 — the
    // kind-domain-exhaustivity ⟺ near-saturation-diagonal pin.
    assert_eq!(
        lacks_only_hits == 1,
        slice.missing_kind_count() == 1,
        "lacks_only_kind holds for some kind iff missing_kind_count() == 1",
    );
    // lacks_only_kind(k) ⟺ has_unique_missing_kind && first_missing_kind() == Some(k)
    // — kind-domain agreement with the arg-less unique-missing predicate.
    for kind in ConditionKind::ALL {
        assert_eq!(
            slice.lacks_only_kind(kind),
            slice.has_unique_missing_kind() && slice.first_missing_kind() == Some(kind),
            "lacks_only_kind({kind:?}) drifted from (has_unique_missing_kind() && first_missing_kind() == Some({kind:?}))",
        );
    }

    // -------- Load-bearing iterator fold: scalar peers ------------------
    //
    // Every scalar closed-set peer folds through the load-bearing
    // iterator peer at ONE substrate site — a regression that overrides
    // ANY scalar peer with a divergent walk (short-circuit skipping a
    // kind, forgetting the negation on the complement side, drifting
    // from `ConditionKind::ALL` order, ignoring the load-bearing
    // iterator entirely with a duplicate closed-set walk of its own)
    // surfaces at THIS arm rather than as silent skew between the
    // scalar callsite and the iterator callsite at every downstream
    // consumer.
    //
    // Complements the Vec-based composition arms above (`distinct_kinds
    // ↔ iter_distinct_kinds`, `distinct_kind_count ↔ distinct_kinds`)
    // by binding each scalar peer DIRECTLY to the iterator surface —
    // catches an override that specializes ONE scalar peer with a
    // divergent walk while leaving the Vec-based intermediate coherent,
    // which the transitive `scalar ↔ Vec ↔ iter` composition arms
    // cannot detect on their own.
    //
    // Peer of tagged-union parent-level substrate testkit
    // `crate::tagged_union::assert_scalar_peers_fold_through_iter_kinds`.
    //
    // -------- Distinct side (folds through iter_distinct_kinds) ---------
    assert_eq!(
        slice.first_distinct_kind(),
        slice.iter_distinct_kinds().next(),
        "first_distinct_kind() drifted from iter_distinct_kinds().next()",
    );
    assert_eq!(
        slice.last_distinct_kind(),
        slice.iter_distinct_kinds().last(),
        "last_distinct_kind() drifted from iter_distinct_kinds().last()",
    );
    assert_eq!(
        slice.has_any_distinct_kind(),
        slice.iter_distinct_kinds().next().is_some(),
        "has_any_distinct_kind() drifted from iter_distinct_kinds().next().is_some()",
    );
    let via_iter_unique_distinct = {
        let mut it = slice.iter_distinct_kinds();
        it.next().is_some() && it.next().is_none()
    };
    assert_eq!(
        slice.has_unique_distinct_kind(),
        via_iter_unique_distinct,
        "has_unique_distinct_kind() drifted from iter_distinct_kinds() two-step short-circuit",
    );
    // -------- Missing side (folds through iter_missing_kinds) -----------
    assert_eq!(
        slice.first_missing_kind(),
        slice.iter_missing_kinds().next(),
        "first_missing_kind() drifted from iter_missing_kinds().next()",
    );
    assert_eq!(
        slice.last_missing_kind(),
        slice.iter_missing_kinds().last(),
        "last_missing_kind() drifted from iter_missing_kinds().last()",
    );
    assert_eq!(
        slice.is_kind_saturated(),
        slice.iter_missing_kinds().next().is_none(),
        "is_kind_saturated() drifted from iter_missing_kinds().next().is_none()",
    );
    let via_iter_unique_missing = {
        let mut it = slice.iter_missing_kinds();
        it.next().is_some() && it.next().is_none()
    };
    assert_eq!(
        slice.has_unique_missing_kind(),
        via_iter_unique_missing,
        "has_unique_missing_kind() drifted from iter_missing_kinds() two-step short-circuit",
    );
    let via_iter_multi_missing = {
        let mut it = slice.iter_missing_kinds();
        it.next().is_some() && it.next().is_some()
    };
    assert_eq!(
        slice.has_multiple_missing_kinds(),
        via_iter_multi_missing,
        "has_multiple_missing_kinds() drifted from iter_missing_kinds() two-step short-circuit",
    );
}

/// Substrate testkit macro — pins the FOUR union composition laws that
/// bind the (precondition, postcondition, union) refinement triads on
/// any authored surface exposing the 12-method (has / find / iter /
/// count) × (pre / post / union) `_kind` matrix. Sweeps
/// [`ConditionKind::ALL`] at ONE call site per authored arrangement.
///
/// # The four surface-level union composition laws
///
/// Where the slice-level substrate primitive
/// [`assert_slice_refinement_composition_laws`] pins the algebra that
/// binds the four refinements *on a single slice* (`iter_kind` →
/// `find_kind` → `has_kind` → `count_kind`), this macro pins the peer
/// algebra one struct-layer up: each refinement's union arm on a
/// two-slice surface (a [`Boundary`] with `preconditions` +
/// `postconditions`, an [`crate::ephemeral::EphemeralSpec`] with the
/// same eponymous field pair) composes from its two half-slice arms
/// through a specific monoid operator baked into the refinement's return
/// type:
///
/// | refinement | half-slice arms                             | union composition                     |
/// |------------|---------------------------------------------|---------------------------------------|
/// | `has_*_kind`   | `has_precondition_kind`, `has_postcondition_kind`     | `pre \|\| post` (bool OR)             |
/// | `find_*_kind`  | `find_precondition_kind`, `find_postcondition_kind`   | `pre.or(post)` (first-Some)           |
/// | `iter_*_kind`  | `iter_precondition_kind`, `iter_postcondition_kind`   | `pre.chain(post)` (stream concat)     |
/// | `count_*_kind` | `count_precondition_kind`, `count_postcondition_kind` | `pre + post` (cardinality SUM)        |
///
/// # Why lift
///
/// Pre-lift each surface-level union composition law lived at its own
/// hand-authored nested-`for` loop test on each of the two surfaces —
/// EIGHT sibling test bodies (`boundary_has_condition_kind_composes_precondition_and_postcondition_arms`,
/// `find_condition_kind_triad_delegates_to_slice_find_kind`,
/// `iter_condition_kind_triad_delegates_to_slice_iter_kind`,
/// `boundary_count_condition_kind_triad_delegates_and_sums_slice_count_kind`
/// on the [`Boundary`] surface, byte-for-byte peers on the
/// [`crate::ephemeral::EphemeralSpec`] surface) whose only per-law knobs
/// were the projection functions being bridged and the composition
/// operator (`\|\|` / `Option::or` / `Iterator::chain` / `+`) applied
/// on top. Post-lift each authored `(preconditions, postconditions)`
/// arrangement pins ALL FOUR union composition laws through ONE
/// `assert_surface_union_composition_laws!(surface)` call whose body
/// is the substrate primitive's own sweep, no per-surface author-time
/// enumeration.
///
/// # Why a macro rather than a `pub fn`
///
/// [`Boundary`] and [`crate::ephemeral::EphemeralSpec`] expose the
/// twelve methods as *inherent* methods with matching signatures. A
/// generic `pub fn assert_surface_union_composition_laws<B: T>(&B)`
/// would need a trait `T` publishing those same twelve methods, and
/// implementing that trait on either surface would collide with the
/// eponymous inherent methods at method resolution — the trait
/// impl would either duplicate the inherent-method bodies verbatim
/// (defeating the lift) or require renaming the trait methods with a
/// `_ext` suffix (introducing a parallel API surface). A macro
/// duck-types at expansion time and hits the inherent methods
/// directly, so both surfaces stay bound through the SAME
/// `_kind`-suffixed method names their non-generic callers already
/// reach for, and the pattern generalizes to any future surface that
/// grows the same twelve-method matrix (an `AplicacaoBoundary` typed
/// wrapper, a `PoolBoundary` gate-carrier at
/// [`crate::pool`], the boundary slot on a
/// hypothetical `AttestationBoundary` receipt-envelope surface) with
/// ONE macro invocation per authored arrangement rather than a per-
/// surface re-authored sweep over the four laws.
///
/// # Compounding
///
/// A FIFTH union refinement added to the (has, find, iter, count)
/// tetrad (a hypothetical `first_params_of_kind(k) -> Option<&Value>`
/// projection combining `find_condition_kind(k).map(|c| &c.params)` at
/// real reconciler callsites, a `distinct_kinds() -> impl Iterator<Item
/// = ConditionKind>` aggregate returning which kinds appear at least
/// once on either side, a `has_kind_matching(pred)` closure-based
/// predicate probe) lands its composition-law pin as ONE new arm
/// inside this macro's body. Every downstream test that already reaches
/// this macro picks up the fifth-refinement pin mechanically — no per-
/// arrangement author-time enumeration of the new law across the four
/// sibling composition-law sites on each of the two surfaces, no
/// re-authored `for kind in ConditionKind::ALL { … }` sweep at every
/// consumer.
///
/// Symmetrical shape to [`assert_slice_refinement_composition_laws`]
/// one layer below: both project a widened-refinement / coarser-
/// refinement composition law contract onto ONE typed substrate call
/// site, both sweep the addressed closed set [`ConditionKind::ALL`],
/// both surface any implementor that overrode the union arm with a
/// divergent composition operator (an `&&` inlined where `\|\|` is
/// required, a `pre - post` inlined where `pre + post` is required,
/// a `zip` inlined where `chain` is required, a `and_then` inlined
/// where `or_else` is required) as a first-class typed test failure
/// rather than as silent operator-facing drift at the
/// `condition-<kind>` / `precondition-<kind>` / `postcondition-<kind>`
/// require-tag classifier surfaces downstream.
///
/// # Theory grounding
///
/// - THEORY.md §II.1 invariant 5 — composition preserves proofs. Each
///   union arm is a typed projection of its two half-slice peers via
///   a specific monoid operator, and this substrate macro turns each
///   projection's composition law from doc-prose into a first-class
///   typed theorem provable against any surface exposing the twelve
///   `_kind`-suffixed inherent methods.
/// - THEORY.md §VI.1 — generation over composition. A new
///   [`ConditionKind`] variant added to `ALL` reaches every downstream
///   union-composition-law consumer through the SAME closed-set sweep
///   with no per-caller edit; a new surface (a typed wrapper carrying
///   the same twelve methods) picks up all four union composition-law
///   pins through ONE macro invocation per authored arrangement.
///
/// # Usage
///
/// ```ignore
/// // Point surface.
/// let mut b = Boundary::default();
/// b.preconditions.push(condition_with(ConditionKind::PromQL));
/// b.postconditions.push(condition_with(ConditionKind::ClosedLoopAuth));
/// assert_surface_union_composition_laws!(b);
///
/// // Ephemeral surface (peer, same primitive).
/// let mut spec = empty_ephemeral();
/// spec.postconditions.push(cond(ConditionKind::JobAttested));
/// assert_surface_union_composition_laws!(spec);
/// ```
#[macro_export]
macro_rules! assert_surface_union_composition_laws {
    ($surface:expr) => {{
        let __surface = &$surface;
        // Hoist distinct_* out of the per-kind loop — closed-set-inversion
        // refinements return the WHOLE distinct-set per call, so a single
        // computation per surface backs the per-kind membership arm inside
        // the loop AND the canonical-order equality after it.
        let __distinct_pre_kinds = __surface.distinct_precondition_kinds();
        let __distinct_post_kinds = __surface.distinct_postcondition_kinds();
        let __distinct_union_kinds = __surface.distinct_condition_kinds();
        let __missing_pre_kinds = __surface.missing_precondition_kinds();
        let __missing_post_kinds = __surface.missing_postcondition_kinds();
        let __missing_union_kinds = __surface.missing_condition_kinds();
        for __kind in $crate::boundary::ConditionKind::ALL {
            // has: union == pre || post (bool OR)
            let __has_via_arms =
                __surface.has_precondition_kind(__kind) || __surface.has_postcondition_kind(__kind);
            ::core::assert_eq!(
                __surface.has_condition_kind(__kind),
                __has_via_arms,
                "surface union has arm drifted from OR of half-slice arms for {:?}",
                __kind,
            );
            // find: union == pre.or(post) (first-Some, kind projection)
            let __find_via_arms = __surface
                .find_precondition_kind(__kind)
                .or(__surface.find_postcondition_kind(__kind))
                .map(|c| c.kind);
            ::core::assert_eq!(
                __surface.find_condition_kind(__kind).map(|c| c.kind),
                __find_via_arms,
                "surface union find arm drifted from precondition.or(postcondition) for {:?}",
                __kind,
            );
            // iter: union == chain(pre, post) (stream concat, kind projection)
            let __iter_via_arms: ::std::vec::Vec<_> = __surface
                .iter_precondition_kind(__kind)
                .chain(__surface.iter_postcondition_kind(__kind))
                .map(|c| c.kind)
                .collect();
            let __iter_via_union: ::std::vec::Vec<_> = __surface
                .iter_condition_kind(__kind)
                .map(|c| c.kind)
                .collect();
            ::core::assert_eq!(
                __iter_via_union,
                __iter_via_arms,
                "surface union iter arm drifted from chain(pre, post) for {:?}",
                __kind,
            );
            // count: union == pre + post (cardinality SUM)
            ::core::assert_eq!(
                __surface.count_condition_kind(__kind),
                __surface.count_precondition_kind(__kind)
                    + __surface.count_postcondition_kind(__kind),
                "surface union count arm drifted from SUM of half-slice arms for {:?}",
                __kind,
            );
            // distinct: union.contains(k) == pre.contains(k) || post.contains(k)
            // (set-union membership per kind on the closed-set-inversion axis)
            ::core::assert_eq!(
                __distinct_union_kinds.contains(&__kind),
                __distinct_pre_kinds.contains(&__kind)
                    || __distinct_post_kinds.contains(&__kind),
                "surface distinct union arm drifted from OR-membership of half-slice distinct arms for {:?}",
                __kind,
            );
            // missing: union.contains(k) == pre.contains(k) && post.contains(k)
            // (set-INTERSECTION membership per kind — a kind is missing
            // from the union iff it is missing from BOTH half-slices,
            // dual of the distinct-set OR composition).
            ::core::assert_eq!(
                __missing_union_kinds.contains(&__kind),
                __missing_pre_kinds.contains(&__kind)
                    && __missing_post_kinds.contains(&__kind),
                "surface missing union arm drifted from AND-membership of half-slice missing arms for {:?}",
                __kind,
            );
            // missing ↔ has: union.contains(k) == !has_condition_kind(k)
            // — binds the missing-set primitive to the point-probe
            // primitive on the surface under a negated predicate.
            ::core::assert_eq!(
                __missing_union_kinds.contains(&__kind),
                !__surface.has_condition_kind(__kind),
                "surface missing union arm drifted from !has_condition_kind for {:?}",
                __kind,
            );
            // lacks: union == pre && post (bool AND — dual of `has`'s
            // `pre || post` OR under `!(a || b) == !a && !b`). A kind is
            // lacked from the union iff BOTH half-slices lack it — the
            // per-kind Boolean-projection peer of the missing-set
            // intersection membership arm above (which composes the SAME
            // AND over the closed-set-complement Vecs); this arm
            // composes it over the per-slice per-kind negation
            // primitives without materializing either side's missing-
            // set Vec. A regression that (a) drifted the union operator
            // to `||` (widening the intersection to a union),
            // (b) dropped the negation on one side, or (c) inverted the
            // wrong slice on the point probe surfaces HERE at the
            // substrate boundary, not as silent drift at every
            // downstream `lacks-<kind>` require-tag classifier callsite.
            let __lacks_via_arms =
                __surface.lacks_precondition_kind(__kind) && __surface.lacks_postcondition_kind(__kind);
            ::core::assert_eq!(
                __surface.lacks_condition_kind(__kind),
                __lacks_via_arms,
                "surface union lacks arm drifted from AND of half-slice lacks arms for {:?}",
                __kind,
            );
            // lacks ↔ has: union == !has_condition_kind(k) — the
            // definitional complement law binds the per-kind Boolean-
            // complement primitive on the surface to the point-probe
            // primitive under negation. Peer of the `missing ↔ has`
            // arm above one refinement lower: the closed-set-complement
            // Vec's per-kind membership equals the per-kind Boolean
            // complement, both equal `!has_condition_kind(k)`. A
            // regression that overrode `lacks_condition_kind` to drop
            // the negation, drift the underlying union primitive, or
            // return `has_condition_kind` surfaces HERE.
            ::core::assert_eq!(
                __surface.lacks_condition_kind(__kind),
                !__surface.has_condition_kind(__kind),
                "surface union lacks arm drifted from !has_condition_kind for {:?}",
                __kind,
            );
        }
        // distinct: union == canonical(pre ∪ post) — closed-set-inversion
        // set-union projected in ConditionKind::ALL order. A regression that
        // (a) reversed the walk order (post-then-pre), (b) preserved
        // slice-encounter order rather than ConditionKind::ALL order, or
        // (c) narrowed the union to an intersection surfaces HERE at the
        // substrate boundary (the per-kind membership arm above catches
        // membership drift; this arm catches ordering + dedup drift the
        // membership arm cannot detect on its own).
        let __expected_distinct_union: ::std::vec::Vec<_> =
            $crate::boundary::ConditionKind::ALL
                .into_iter()
                .filter(|__k| {
                    __distinct_pre_kinds.contains(__k)
                        || __distinct_post_kinds.contains(__k)
                })
                .collect();
        ::core::assert_eq!(
            __distinct_union_kinds, __expected_distinct_union,
            "surface distinct union arm drifted from canonical ConditionKind::ALL-ordered set-union of half-slice distinct arms",
        );
        // missing: union == canonical(pre ∩ post) — closed-set-inversion
        // set-INTERSECTION projected in ConditionKind::ALL order. Dual
        // of the distinct union canonical-order arm above. A regression
        // that (a) reversed the walk order, (b) widened the intersection
        // to a union (returning kinds missing from either side rather
        // than both), or (c) preserved slice-encounter order rather
        // than ConditionKind::ALL order surfaces HERE at the substrate
        // boundary.
        let __expected_missing_union: ::std::vec::Vec<_> =
            $crate::boundary::ConditionKind::ALL
                .into_iter()
                .filter(|__k| {
                    __missing_pre_kinds.contains(__k)
                        && __missing_post_kinds.contains(__k)
                })
                .collect();
        ::core::assert_eq!(
            __missing_union_kinds, __expected_missing_union,
            "surface missing union arm drifted from canonical ConditionKind::ALL-ordered set-INTERSECTION of half-slice missing arms",
        );
    }};
}

/// A single boundary predicate.
#[derive(Clone, Debug, Serialize, Deserialize, JsonSchema)]
#[serde(rename_all = "camelCase")]
pub struct Condition {
    pub kind: ConditionKind,
    /// Kind-specific payload (free-form JSON).
    #[serde(default)]
    #[schemars(schema_with = "crate::schema_helpers::preserve_unknown_object")]
    pub params: serde_json::Value,
}

#[derive(
    Clone,
    Copy,
    Debug,
    PartialEq,
    Eq,
    Hash,
    Serialize,
    Deserialize,
    JsonSchema,
    tatara_closed_set::DeriveClosedSet,
)]
#[serde(rename_all = "PascalCase")]
#[closed_set(via = "as_str", display, generate_unknown)]
pub enum ConditionKind {
    /// Another Process must be in a given phase.
    /// `params`: `{ "processRef": "...", "namespace": "...", "phase": "Attested" }`
    ProcessPhase,
    /// FluxCD `Kustomization.status.conditions[type=Ready]` must be `True`.
    /// `params`: `{ "name": "...", "namespace": "flux-system" }`
    KustomizationHealthy,
    /// FluxCD `HelmRelease.status.conditions[type=Ready]` must be `True`.
    /// `params`: `{ "name": "...", "namespace": "..." }`
    HelmReleaseReleased,
    /// Prometheus query — truthy scalar required.
    /// `params`: `{ "query": "..." }`
    PromQL,
    /// CEL expression over a scoped object set.
    /// `params`: `{ "expression": "..." }`
    Cel,
    /// Nix evaluation equality check.
    /// `params`: `{ "flakeRef": "...", "attribute": "...", "expect": "..." }`
    NixEval,
    /// A Kubernetes Job must complete successfully and its emitted BLAKE3
    /// receipt must verify.
    /// `params`: `{ "name": "...", "namespace": "...", "expectReceipt": true }`
    JobAttested,
    /// Closed-loop authentication probe — the canonical postcondition for
    /// any system that can produce credentials for its own client under
    /// test. The probe Job (rendered by the VERIFY handler) fetches a
    /// fresh secret from `issuer` (a Service inside the same namespace),
    /// presents it to `consumer` (another Service in the same namespace),
    /// and verifies that `consumer` authenticated successfully against
    /// `jwk_source` (the issuer's published JWK endpoint).
    ///
    /// The Job emits a three-pillar BLAKE3 receipt that the reconciler
    /// chains into `status.attestation`. This turns "the gateway↔SaaS
    /// loop holds" from an assertion into a theorem provable for every
    /// ephemeral run.
    ///
    /// `params`:
    /// ```json
    /// {
    ///   "issuer":   { "service": "demo-app-issuer",
    ///                 "port": 8080,
    ///                 "secretPath": "/v2/get-secret-value" },
    ///   "consumer": { "service": "demo-app-gateway",
    ///                 "port": 8000,
    ///                 "authPath": "/api/v3/auth" },
    ///   "jwkSource":{ "service": "demo-app-issuer",
    ///                 "port": 8080,
    ///                 "path": "/.well-known/jwks.json" },
    ///   "probeImage": "ghcr.io/pleme-io/closed-loop-probe:0.1.0",
    ///   "timeoutSeconds": 120
    /// }
    /// ```
    ClosedLoopAuth,
}

impl ConditionKind {
    /// The closed set of boundary-condition kinds the reconciler honors.
    /// Single source of truth that drives the `as_str` / Display /
    /// `FromStr` triad on this enum and the `stub_message` lift of the
    /// "not yet implemented" arms the reconciler used to hand-roll three
    /// times. Adding a 9th variant lands at one `ALL` entry + one `as_str`
    /// arm + one `stub_message` arm — exhaustively checked by the
    /// compiler (the array literal forces arity).
    ///
    /// Sibling closed-set lifts: [`crate::phase::ProcessPhase::ALL`],
    /// [`crate::signal::ProcessSignal::ALL`], [`crate::intent::IntentKind::ALL`],
    /// [`crate::lifetime::LifetimeKind::ALL`].
    pub const ALL: [Self; 8] = [
        Self::ProcessPhase,
        Self::KustomizationHealthy,
        Self::HelmReleaseReleased,
        Self::PromQL,
        Self::Cel,
        Self::NixEval,
        Self::JobAttested,
        Self::ClosedLoopAuth,
    ];

    /// Canonical PascalCase wire-format projection — matches the serde
    /// `rename_all = "PascalCase"` output verbatim. Used by Display
    /// (single source of truth), by `FromStr` to identify the variant
    /// from its annotation / status-field representation, and by
    /// operator-facing diagnostics that need the kind name without
    /// re-serializing the enum through serde_json. Pinned by
    /// `condition_kind_as_str_matches_serde`.
    pub const fn as_str(self) -> &'static str {
        match self {
            Self::ProcessPhase => "ProcessPhase",
            Self::KustomizationHealthy => "KustomizationHealthy",
            Self::HelmReleaseReleased => "HelmReleaseReleased",
            Self::PromQL => "PromQL",
            Self::Cel => "Cel",
            Self::NixEval => "NixEval",
            Self::JobAttested => "JobAttested",
            Self::ClosedLoopAuth => "ClosedLoopAuth",
        }
    }

    /// The operator-facing "evaluator not yet implemented" message for
    /// stub kinds — `Some` iff this kind has no live evaluator wired in
    /// `tatara-reconciler::boundary`. ONE site owns the per-kind stub
    /// string; the reconciler's dispatch reaches for this projection
    /// instead of hand-rolling three parallel `Unknown(...)` strings.
    ///
    /// A future variant added as a live evaluator returns `None`; a
    /// future variant added as a stub returns `Some("<kind> evaluator
    /// not yet implemented")` — both reachable through one match
    /// instead of three identical-shape arms drifting in parallel.
    pub const fn stub_message(self) -> Option<&'static str> {
        match self {
            Self::PromQL => Some("PromQL evaluator not yet implemented"),
            Self::Cel => Some("CEL evaluator not yet implemented"),
            Self::NixEval => Some("NixEval evaluator not yet implemented"),
            Self::ProcessPhase
            | Self::KustomizationHealthy
            | Self::HelmReleaseReleased
            | Self::JobAttested
            | Self::ClosedLoopAuth => None,
        }
    }

    /// True iff this kind has no live evaluator (its [`Self::stub_message`]
    /// is `Some`). Pairs with the reconciler's `evaluate` dispatch — a
    /// stub kind unconditionally yields `Satisfaction::Unknown`.
    pub const fn is_stub(self) -> bool {
        self.stub_message().is_some()
    }

    /// The [`FluxResource`] variant this condition kind fetches from
    /// the K8s API server, or `None` for non-Flux-fetching kinds — the
    /// typed projection owning the (ConditionKind → FluxResource)
    /// association every reconciler `evaluate` dispatch arm and every
    /// future coherence check binds through.
    ///
    /// Pre-lift the association was open-coded at TWO adjacent
    /// `evaluate` arms in `tatara-reconciler::boundary::evaluate` past
    /// the ★★ PRIME-DIRECTIVE ≥ 2 duplication threshold — each arm
    /// hand-authored a `(FluxResource::X.api_version(),
    /// FluxResource::X.kind())` pair as the two `&str` slots the
    /// pre-lift `evaluate_flux_ready(api_version: &str, kind: &str)`
    /// signature required. Post-lift the mapping lives at ONE typed
    /// projection here, the callee accepts a typed
    /// [`FluxResource`] slot (invalid `(apiVersion, kind)` pairings
    /// like Kustomization's apiVersion paired with HelmRelease's kind
    /// become unrepresentable), and the two `evaluate` arms collapse
    /// onto ONE `KustomizationHealthy | HelmReleaseReleased` OR-arm
    /// that reads the FluxResource variant from `.flux_resource()`.
    ///
    /// A future ConditionKind that fetches a fourth Flux resource
    /// variant (a hypothetical `BucketSynced` kind against a Flux
    /// `Bucket` source) lands as ONE new arm here + ONE new variant
    /// on [`FluxResource`] + ONE OR-pattern extension at the
    /// reconciler dispatch — no hand-authored `(apiVersion, kind)`
    /// pair at the callsite, no widening of the callee's signature.
    ///
    /// The three current non-Flux-fetching arms return `None`:
    /// - `ProcessPhase` fetches a tatara `Process` (through its own
    ///   [`crate::api_version`] + [`crate::PROCESS_KIND`] pair, not
    ///   a Flux `(apiVersion, kind)`).
    /// - `JobAttested` / `ClosedLoopAuth` fetch a `batch/v1::Job` +
    ///   an optional receipt `v1::ConfigMap`, both K8s built-ins
    ///   (not Flux resources).
    /// - `PromQL` / `Cel` / `NixEval` are stub evaluators
    ///   ([`Self::is_stub`]) — no cluster fetch at all.
    ///
    /// Theory anchor: THEORY.md §II.1 invariant 5 (composition
    /// preserves proofs — the (ConditionKind → FluxResource)
    /// association lives at ONE typed algebra projection here, not
    /// at every reconciler dispatch arm).
    pub const fn flux_resource(self) -> Option<FluxResource> {
        match self {
            Self::KustomizationHealthy => Some(FluxResource::Kustomization),
            Self::HelmReleaseReleased => Some(FluxResource::HelmRelease),
            Self::ProcessPhase
            | Self::PromQL
            | Self::Cel
            | Self::NixEval
            | Self::JobAttested
            | Self::ClosedLoopAuth => None,
        }
    }
}

// `impl fmt::Display for ConditionKind` + `impl FromStr for
// ConditionKind` + `impl tatara_lisp::ClosedSet for ConditionKind` +
// `pub struct UnknownConditionKind(pub String)` are generated by
// `#[derive(tatara_closed_set::DeriveClosedSet)]` + `#[closed_set(via =
// "as_str", display, generate_unknown)]` on the enum declaration above.
// The auto-derived label `"condition kind"` matches the prior hand-
// rolled `#[error("unknown condition kind: {0}")]` verbatim. The
// inherent `as_str` projection stays load-bearing — the PascalCase
// wire-format that matches the serde rename + the CRD `enum:` listing
// verbatim (notably preserving `PromQL`'s consecutive caps that heck
// would have lowercased) — while the trait method `label` gives
// generic consumers a STABLE name across the 36+ workspace-wide
// closed-set implementors.

#[cfg(test)]
mod tests {
    use super::*;
    use serde_json::json;

    #[test]
    fn serde_process_phase_condition() {
        let c = Condition {
            kind: ConditionKind::ProcessPhase,
            params: json!({ "processRef": "secret-injection", "phase": "Attested" }),
        };
        let yaml = serde_yaml::to_string(&c).unwrap();
        assert!(yaml.contains("kind: ProcessPhase"));
        assert!(yaml.contains("processRef: secret-injection"));
    }

    #[test]
    fn serde_closed_loop_auth_condition() {
        let c = Condition {
            kind: ConditionKind::ClosedLoopAuth,
            params: json!({
                "issuer":   { "service": "demo-app-issuer", "port": 8080 },
                "consumer": { "service": "demo-app-gateway", "port": 8000 },
                "probeImage": "ghcr.io/pleme-io/closed-loop-probe:0.1.0",
            }),
        };
        let yaml = serde_yaml::to_string(&c).unwrap();
        assert!(yaml.contains("kind: ClosedLoopAuth"));
        assert!(yaml.contains("probeImage: ghcr.io/pleme-io/closed-loop-probe:0.1.0"));
        let back: Condition = serde_yaml::from_str(&yaml).unwrap();
        assert_eq!(back.kind, ConditionKind::ClosedLoopAuth);
    }

    #[test]
    fn serde_job_attested_condition() {
        let c = Condition {
            kind: ConditionKind::JobAttested,
            params: json!({ "name": "seed-job", "namespace": "demo-test" }),
        };
        let yaml = serde_yaml::to_string(&c).unwrap();
        assert!(yaml.contains("kind: JobAttested"));
    }

    // ── closed-set algebra contracts (ALL × as_str × FromStr × stub_message) ─

    /// Structural well-formedness of [`ConditionKind`] as a
    /// [`tatara_lisp::ClosedSet`] implementor — the workspace-wide
    /// testkit lift that pins all three structural invariants (`ALL`
    /// is non-empty, every variant round-trips through `label ↔
    /// parse_label`, labels are pairwise distinct, `""` is outside the
    /// closed set) at ONE call site. Replaces the hand-derived
    /// `condition_kind_all_is_unique_and_complete` +
    /// `condition_kind_roundtrip_via_as_str` + the empty-input arm of
    /// `unknown_condition_kind_errors`. `FromStr` delegates to
    /// `<Self as tatara_closed_set::ClosedSet>::parse_label`, so this helper
    /// exercises the same code path the reconciler hits when parsing a
    /// CRD `enum:`-validated value back to the typed kind.
    #[test]
    fn condition_kind_is_well_formed_closed_set() {
        tatara_closed_set::assert_closed_set_well_formed::<ConditionKind>();
    }

    /// CANONICAL-KEY CONTRACT: `as_str` matches serde's PascalCase
    /// output verbatim for every variant. A future variant rename
    /// (or an `as_str` arm typo) lands here at one site. The probe
    /// confirmed `PromQL` survives `rename_all = "PascalCase"` as
    /// `"PromQL"` (heck preserves consecutive caps in the leading
    /// word), so this contract is the operator-facing pin.
    #[test]
    fn condition_kind_as_str_matches_serde() {
        crate::tagged_union::assert_label_matches_serde_serialization::<ConditionKind>();
    }

    /// The Display impl IS `as_str` — pinning this lets future
    /// callers reach for either projection without drift. If a
    /// reviewer accidentally re-introduces an inline match in
    /// Display, this fails the moment a variant rename touches one
    /// site but not the other.
    #[test]
    fn condition_kind_display_matches_as_str() {
        crate::tagged_union::assert_display_matches_label::<ConditionKind>();
    }

    /// `FromStr` rejects strings that aren't in the canonical
    /// projection — lowercased / typo / unrelated — and the error
    /// echoes the input verbatim so the operator-facing diagnostic
    /// carries the offending value, not a normalized form. The
    /// empty-input arm is pinned by
    /// [`condition_kind_is_well_formed_closed_set`] via the
    /// `tatara_lisp::ClosedSet` testkit; the cases here pin the
    /// verbatim-echo contract on the [`UnknownConditionKind`]
    /// newtype, which the trait's `make_unknown` can't see.
    #[test]
    fn unknown_condition_kind_errors() {
        use std::str::FromStr;
        for bad in ["processPhase", "PROMQL", "Promql", "Bogus"] {
            let err = ConditionKind::from_str(bad).unwrap_err();
            assert_eq!(err.0, bad, "error payload should echo input verbatim");
        }
    }

    /// STUB CONTRACT: the three placeholder evaluators
    /// (PromQL / Cel / NixEval) are exactly the set whose
    /// `stub_message` is `Some`. The five live evaluators return
    /// `None`. A future variant promoted from stub → live must drop
    /// its `stub_message` arm; a new stub must add one. Both
    /// transitions land at this test by sweeping ALL.
    #[test]
    fn condition_kind_stub_set_matches_stubs() {
        use ConditionKind::*;
        for kind in ConditionKind::ALL {
            let expected_is_stub = matches!(kind, PromQL | Cel | NixEval);
            assert_eq!(
                kind.is_stub(),
                expected_is_stub,
                "is_stub disagreed for {kind:?}",
            );
            assert_eq!(
                kind.stub_message().is_some(),
                expected_is_stub,
                "stub_message disagreed for {kind:?}",
            );
        }
    }

    /// Pin the exact stub strings so a rename of the operator-facing
    /// "not yet implemented" message lands at one site (here) instead
    /// of three parallel inline strings in the reconciler.
    #[test]
    fn condition_kind_stub_messages_are_pinned() {
        assert_eq!(
            ConditionKind::PromQL.stub_message(),
            Some("PromQL evaluator not yet implemented"),
        );
        assert_eq!(
            ConditionKind::Cel.stub_message(),
            Some("CEL evaluator not yet implemented"),
        );
        assert_eq!(
            ConditionKind::NixEval.stub_message(),
            Some("NixEval evaluator not yet implemented"),
        );
    }

    // ── (ConditionKind → FluxResource) typed projection contracts ────

    /// The two Flux-fetching kinds project to their canonical
    /// [`FluxResource`] variants. A future ConditionKind rename or
    /// FluxResource variant rename that skewed the projection at ONE
    /// arm surfaces here.
    #[test]
    fn kustomization_healthy_projects_to_flux_resource_kustomization() {
        assert_eq!(
            ConditionKind::KustomizationHealthy.flux_resource(),
            Some(FluxResource::Kustomization),
        );
    }

    #[test]
    fn helm_release_released_projects_to_flux_resource_helm_release() {
        assert_eq!(
            ConditionKind::HelmReleaseReleased.flux_resource(),
            Some(FluxResource::HelmRelease),
        );
    }

    /// The six non-Flux-fetching kinds project to `None`. Sweeps
    /// `ConditionKind::ALL` filtering by `flux_resource().is_none()`
    /// so a new variant added without a `flux_resource` arm surfaces
    /// at rustc's non-exhaustive-match gate BEFORE this test even
    /// runs; a new variant added with a hand-coded `Some(...)` arm
    /// that shouldn't fetch Flux surfaces here.
    #[test]
    fn non_flux_fetching_kinds_project_to_none() {
        use ConditionKind::*;
        let non_flux: Vec<_> = ConditionKind::ALL
            .iter()
            .copied()
            .filter(|k| k.flux_resource().is_none())
            .collect();
        assert_eq!(
            non_flux,
            vec![
                ProcessPhase,
                PromQL,
                Cel,
                NixEval,
                JobAttested,
                ClosedLoopAuth
            ],
        );
    }

    /// Every variant of [`ConditionKind`] whose `flux_resource()` is
    /// `Some` uniquely names its FluxResource variant (no two
    /// ConditionKind arms may fetch the SAME FluxResource — that
    /// would signal a redundant closed-set entry). Peers the
    /// `every_variants_api_version_and_kind_are_distinct_across_the_closed_set`
    /// pin on the sibling [`FluxResource`] closed set.
    #[test]
    fn flux_resource_projection_is_injective_on_the_some_arms() {
        let mut seen = std::collections::HashSet::new();
        for k in ConditionKind::ALL {
            if let Some(fr) = k.flux_resource() {
                assert!(
                    seen.insert(fr),
                    "duplicate FluxResource projection at {k:?}: {fr:?}",
                );
            }
        }
    }

    /// `flux_resource` is `const fn` — the projection is reachable
    /// at compile time. A regression that dropped the `const`
    /// qualifier would fail-loudly here rather than as a wrong-slot
    /// runtime dispatch at every consumer callsite.
    #[test]
    fn flux_resource_projection_is_const_fn_reachable() {
        const K: Option<FluxResource> = ConditionKind::KustomizationHealthy.flux_resource();
        const H: Option<FluxResource> = ConditionKind::HelmReleaseReleased.flux_resource();
        const P: Option<FluxResource> = ConditionKind::ProcessPhase.flux_resource();
        assert_eq!(K, Some(FluxResource::Kustomization));
        assert_eq!(H, Some(FluxResource::HelmRelease));
        assert_eq!(P, None);
    }

    // ── Boundary::has_condition_kind substrate pins ──────────────────
    //
    // Fail-before-pass-after granularity: `Boundary::has_condition_kind`
    // did not exist before this commit — the (preconditions +
    // postconditions .iter().any(|c| c.kind == K)) union-probe shape
    // lived hand-authored inline at the ephemeral require-tag surface
    // (`spec.postconditions.iter().any(|c| matches!(c.kind, K))`, sans
    // the pre-condition side). The lift places the closed-set-driven
    // presence probe on ONE substrate site so the point-domain
    // `condition-<kind>` prefix family in `tatara-check` composes it
    // through `strip_and_classify_prefixed_kind` byte-for-byte
    // symmetrical with `intent-<kind>` (via `Intent::has`) +
    // `lifetime-<kind>` (via `Lifetime::has`) — third instance in the
    // workspace closed-set-driven presence-probe algebra.

    fn condition_with(kind: ConditionKind) -> Condition {
        Condition {
            kind,
            params: json!({}),
        }
    }

    /// EMPTY-BOUNDARY pin — a default [`Boundary`] (no preconditions,
    /// no postconditions) returns `false` for EVERY [`ConditionKind`].
    /// Sweep `ConditionKind::ALL` so a new variant added without a
    /// matching arm in the presence probe surfaces at rustc's
    /// exhaustiveness gate on the ALL literal (arity forced by
    /// `[Self; 8]`) rather than as a silent false-positive at every
    /// downstream `condition-<kind>` require-tag callsite.
    #[test]
    fn has_condition_kind_returns_false_on_empty_boundary_for_every_kind() {
        let b = Boundary::default();
        for kind in ConditionKind::ALL {
            assert!(
                !b.has_condition_kind(kind),
                "default boundary must return false for {kind:?}",
            );
        }
    }

    /// POSTCONDITION-only pin — a boundary that carries the kind on
    /// ONLY postconditions returns `true` for that kind, `false` for
    /// every other variant. Sweep the ALL × ALL cross so a regression
    /// that (a) hard-coded the arm to a single kind (silently
    /// returning true for every populated boundary regardless of
    /// which kind was queried), (b) skipped the postcondition side of
    /// the union (silently returning false when the kind lived
    /// post-only), or (c) matched on Condition::params instead of
    /// Condition::kind fails HERE at the substrate primitive.
    #[test]
    fn has_condition_kind_reads_postconditions_per_kind() {
        for populated in ConditionKind::ALL {
            let mut b = Boundary::default();
            b.postconditions.push(condition_with(populated));
            for query in ConditionKind::ALL {
                let expected = query == populated;
                assert_eq!(
                    b.has_condition_kind(query),
                    expected,
                    "postcondition populated={populated:?}: query {query:?} drifted",
                );
            }
        }
    }

    /// PRECONDITION-only pin — mirrors the postcondition sweep on the
    /// other half of the union. Locks the union semantics on both
    /// halves separately so a regression that dropped the
    /// pre-condition side of the OR fails here even though the
    /// postcondition-side pin above passes.
    #[test]
    fn has_condition_kind_reads_preconditions_per_kind() {
        for populated in ConditionKind::ALL {
            let mut b = Boundary::default();
            b.preconditions.push(condition_with(populated));
            for query in ConditionKind::ALL {
                let expected = query == populated;
                assert_eq!(
                    b.has_condition_kind(query),
                    expected,
                    "precondition populated={populated:?}: query {query:?} drifted",
                );
            }
        }
    }

    /// UNION pin — a kind that appears on preconditions returns
    /// `true` even when postconditions carries a DIFFERENT kind, and
    /// vice versa. Pins the OR-composition of the two halves so a
    /// regression that collapsed the union to an intersection (AND)
    /// silently reclassifies pre-only or post-only kinds as absent.
    #[test]
    fn has_condition_kind_unions_pre_and_post_condition_arms() {
        let mut b = Boundary::default();
        b.preconditions
            .push(condition_with(ConditionKind::KustomizationHealthy));
        b.postconditions
            .push(condition_with(ConditionKind::ClosedLoopAuth));
        assert!(
            b.has_condition_kind(ConditionKind::KustomizationHealthy),
            "pre-only kind must resolve through the union",
        );
        assert!(
            b.has_condition_kind(ConditionKind::ClosedLoopAuth),
            "post-only kind must resolve through the union",
        );
        assert!(
            !b.has_condition_kind(ConditionKind::PromQL),
            "an absent kind must return false even with populated halves",
        );
    }

    // ── ConditionSliceExt::has_kind substrate pins ────────────────────
    //
    // Fail-before-pass-after granularity: `ConditionSliceExt::has_kind`
    // did not exist before this commit — the `(&[Condition],
    // ConditionKind) -> bool` walk shape lived hand-authored inline at
    // THREE production sites (twice inside `Boundary::has_condition_kind`
    // on `preconditions` ∪ `postconditions`, once at the ephemeral
    // require-tag classifier's `closed-loop-auth` arm on
    // `spec.postconditions` in `tatara-reconciler::bin::tatara-check`,
    // with `matches!` sugar instead of `==` but the same predicate).
    // The lift places the per-slice presence probe on ONE substrate site
    // so the two-half union at `Boundary` and the one-half probe at the
    // ephemeral surface compose against the SAME primitive rather than
    // restating the `.iter().any(|c| c.kind == K)` closure body.

    /// EMPTY-SLICE pin — an empty `&[Condition]` returns `false` for
    /// EVERY [`ConditionKind`]. Sweep `ConditionKind::ALL` so a new
    /// variant added without a matching arm in the primitive surfaces
    /// at rustc's exhaustiveness gate on the ALL literal (arity forced
    /// by `[Self; 8]`) rather than as a silent false-positive at every
    /// downstream callsite composing this primitive.
    #[test]
    fn condition_slice_has_kind_returns_false_on_empty_slice_for_every_kind() {
        let empty: &[Condition] = &[];
        for kind in ConditionKind::ALL {
            assert!(
                !empty.has_kind(kind),
                "empty slice must return false for {kind:?}",
            );
        }
    }

    /// PER-VARIANT pin — a single-element slice returns `true` for
    /// exactly the kind it carries, `false` for every other variant.
    /// Sweep the ALL × ALL cross so a regression that (a) hard-coded
    /// the arm to a single kind (silently returning true for every
    /// populated slice regardless of query kind), or (b) matched on
    /// [`Condition::params`] instead of [`Condition::kind`] fails HERE
    /// at the substrate primitive.
    #[test]
    fn condition_slice_has_kind_reads_kind_field_per_variant() {
        for populated in ConditionKind::ALL {
            let slice = [condition_with(populated)];
            for query in ConditionKind::ALL {
                let expected = query == populated;
                assert_eq!(
                    slice.has_kind(query),
                    expected,
                    "populated={populated:?}: query {query:?} drifted",
                );
            }
        }
    }

    /// MULTI-ENTRY pin — a slice with multiple entries returns `true`
    /// for every kind that appears at any position (existential
    /// quantifier over the slice), `false` for kinds that appear at
    /// no position. Locks the `any` semantics so a regression that
    /// collapsed to a `first`-only probe (`slice.first().map_or(false,
    /// |c| c.kind == kind)`) fails here even though the single-element
    /// per-variant pin above passes.
    #[test]
    fn condition_slice_has_kind_scans_beyond_the_first_position() {
        let slice = [
            condition_with(ConditionKind::KustomizationHealthy),
            condition_with(ConditionKind::ClosedLoopAuth),
            condition_with(ConditionKind::JobAttested),
        ];
        for present in [
            ConditionKind::KustomizationHealthy,
            ConditionKind::ClosedLoopAuth,
            ConditionKind::JobAttested,
        ] {
            assert!(
                slice.has_kind(present),
                "kind at any position must resolve true: {present:?}",
            );
        }
        for absent in [
            ConditionKind::ProcessPhase,
            ConditionKind::HelmReleaseReleased,
            ConditionKind::PromQL,
            ConditionKind::Cel,
            ConditionKind::NixEval,
        ] {
            assert!(
                !slice.has_kind(absent),
                "kind absent from the slice must resolve false: {absent:?}",
            );
        }
    }

    /// COMPOSITION pin — [`Boundary::has_condition_kind`] equals the OR
    /// of the two half-slice probes at EVERY (populated arrangement,
    /// query) pair on `ConditionKind::ALL`. Locks the (union-probe =
    /// pre.has_kind ∨ post.has_kind) composition contract at ONE test
    /// so a regression that (a) dropped the `||` (silently narrowing
    /// the union to an intersection, or to one side only), or
    /// (b) hand-authored the union with a divergent walk shape (e.g.
    /// summing counts, comparing lengths) surfaces HERE at the
    /// composition boundary rather than as silent classifier drift at
    /// every downstream `condition-<kind>` require-tag callsite.
    #[test]
    fn boundary_has_condition_kind_equals_or_of_half_slice_probes() {
        for pre_kind in ConditionKind::ALL {
            for post_kind in ConditionKind::ALL {
                let mut b = Boundary::default();
                b.preconditions.push(condition_with(pre_kind));
                b.postconditions.push(condition_with(post_kind));
                for query in ConditionKind::ALL {
                    let expected =
                        b.preconditions.has_kind(query) || b.postconditions.has_kind(query);
                    assert_eq!(
                        b.has_condition_kind(query),
                        expected,
                        "union drifted: pre={pre_kind:?} post={post_kind:?} query={query:?}",
                    );
                }
            }
        }
    }

    // ── Boundary::has_(pre|post)condition_kind substrate pins ────────
    //
    // Fail-before-pass-after granularity: the two half-slice arms did
    // not exist before this commit — the point-domain `precondition-
    // <kind>` and `postcondition-<kind>` require-tag classifiers in
    // `tatara-reconciler::bin::tatara-check` reached the two condition
    // slices through direct field access
    // (`spec.boundary.preconditions.has_kind(k)`), bypassing the named
    // [`Boundary`] primitive surface that the union-probe
    // [`Boundary::has_condition_kind`] already routed through. The
    // lift closes the (precondition, postcondition, union) triad on
    // ONE typed algebra surface so a future normalization at the
    // presence-probe shape lands at ONE site for all three arms.

    /// EMPTY-BOUNDARY pin (precondition arm) — a default [`Boundary`]
    /// returns `false` for EVERY [`ConditionKind`] on the precondition
    /// side. Sweep `ConditionKind::ALL` so a new variant added without
    /// a matching arm on the probe surfaces at rustc's exhaustiveness
    /// gate on the ALL literal (arity forced by `[Self; 8]`) rather
    /// than as a silent false-positive at every downstream
    /// `precondition-<kind>` require-tag callsite.
    #[test]
    fn has_precondition_kind_returns_false_on_empty_boundary_for_every_kind() {
        let b = Boundary::default();
        for kind in ConditionKind::ALL {
            assert!(
                !b.has_precondition_kind(kind),
                "default boundary must return false on precondition arm for {kind:?}",
            );
        }
    }

    /// EMPTY-BOUNDARY pin (postcondition arm) — sibling of the
    /// precondition-arm empty pin above on the other half of the
    /// (precondition, postcondition) partition. Locks the empty-slice
    /// arm return on the postcondition side so a regression that
    /// wired the postcondition arm to the precondition slice surfaces
    /// HERE at fail-before-pass-after granularity.
    #[test]
    fn has_postcondition_kind_returns_false_on_empty_boundary_for_every_kind() {
        let b = Boundary::default();
        for kind in ConditionKind::ALL {
            assert!(
                !b.has_postcondition_kind(kind),
                "default boundary must return false on postcondition arm for {kind:?}",
            );
        }
    }

    /// SLICE-SELECTIVITY pin (precondition arm) — a boundary with a
    /// kind on the precondition side ONLY resolves `true` at
    /// `has_precondition_kind` and `false` at `has_postcondition_kind`.
    /// Locks the (side-select, kind-select) partition so a regression
    /// that pointed the precondition arm at `self.postconditions` (a
    /// copy-paste from the sibling arm) surfaces HERE rather than as
    /// silent classifier drift at every downstream
    /// `precondition-<kind>` require-tag callsite.
    #[test]
    fn has_precondition_kind_reads_preconditions_slice_only() {
        for populated in ConditionKind::ALL {
            let mut b = Boundary::default();
            b.preconditions.push(condition_with(populated));
            for query in ConditionKind::ALL {
                let expected_pre = query == populated;
                assert_eq!(
                    b.has_precondition_kind(query),
                    expected_pre,
                    "precondition-only populated={populated:?}: query {query:?} drifted \
                     on precondition arm",
                );
                assert!(
                    !b.has_postcondition_kind(query),
                    "precondition-only populated={populated:?}: query {query:?} must \
                     return false on postcondition arm (postconditions is empty)",
                );
            }
        }
    }

    /// SLICE-SELECTIVITY pin (postcondition arm) — mirror of the
    /// precondition-only sweep on the other half. Locks the sibling
    /// arm's binding to `self.postconditions` so a regression that
    /// pointed the postcondition arm at `self.preconditions` fails
    /// HERE even though the precondition-arm pin above passes.
    #[test]
    fn has_postcondition_kind_reads_postconditions_slice_only() {
        for populated in ConditionKind::ALL {
            let mut b = Boundary::default();
            b.postconditions.push(condition_with(populated));
            for query in ConditionKind::ALL {
                let expected_post = query == populated;
                assert_eq!(
                    b.has_postcondition_kind(query),
                    expected_post,
                    "postcondition-only populated={populated:?}: query {query:?} \
                     drifted on postcondition arm",
                );
                assert!(
                    !b.has_precondition_kind(query),
                    "postcondition-only populated={populated:?}: query {query:?} must \
                     return false on precondition arm (preconditions is empty)",
                );
            }
        }
    }

    /// COMPOSITION-LAW pin — [`Boundary::has_condition_kind`] equals
    /// `has_precondition_kind(k) || has_postcondition_kind(k)` at
    /// EVERY (pre-populated, post-populated, query) triple on
    /// `ConditionKind::ALL`. This is the load-bearing invariant that
    /// makes the (precondition, postcondition, union) triad on
    /// [`Boundary`] a first-class typed algebra rather than a
    /// per-caller discipline: the two half-slice arms + the union arm
    /// compose exactly as `union == pre ∨ post`, and every downstream
    /// `condition-<K> = precondition-<K> ∨ postcondition-<K>` classifier
    /// invariant on `tatara-reconciler::bin::tatara-check` inherits it
    /// mechanically. A regression that (a) dropped the composition (by
    /// re-inlining `.has_kind(kind)` bodies on the union arm), or
    /// (b) drifted ONE of the two half-slice arms without updating the
    /// other, surfaces HERE rather than as silent per-side classifier
    /// drift at the require-tag surfaces.
    #[test]
    fn boundary_has_condition_kind_composes_precondition_and_postcondition_arms() {
        for pre_kind in ConditionKind::ALL {
            for post_kind in ConditionKind::ALL {
                let mut b = Boundary::default();
                b.preconditions.push(condition_with(pre_kind));
                b.postconditions.push(condition_with(post_kind));
                for query in ConditionKind::ALL {
                    let via_arms =
                        b.has_precondition_kind(query) || b.has_postcondition_kind(query);
                    assert_eq!(
                        b.has_condition_kind(query),
                        via_arms,
                        "union arm drifted from OR of half-slice arms: \
                         pre={pre_kind:?} post={post_kind:?} query={query:?}",
                    );
                }
            }
        }
    }

    /// SUBSTRATE-DELEGATION pin — the two half-slice arms delegate
    /// verbatim to [`ConditionSliceExt::has_kind`] on the underlying
    /// [`Vec<Condition>`] slice, no inline reimplementation. Sweep the
    /// full `ConditionKind::ALL` × `ConditionKind::ALL` cross so a
    /// regression that inlined a divergent walk (`.iter().find(_).
    /// is_some()`, an `.any(|c| matches!(c.kind, K))` that missed a
    /// variant) at either arm surfaces HERE at the substrate
    /// boundary rather than as silent skew between the struct-level
    /// arm and the slice-level primitive downstream consumers reach
    /// through.
    #[test]
    fn has_precondition_and_postcondition_kind_delegate_to_slice_has_kind() {
        for populated in ConditionKind::ALL {
            let mut b = Boundary::default();
            b.preconditions.push(condition_with(populated));
            b.postconditions.push(condition_with(populated));
            for query in ConditionKind::ALL {
                assert_eq!(
                    b.has_precondition_kind(query),
                    b.preconditions.has_kind(query),
                    "precondition arm must delegate to preconditions.has_kind: \
                     populated={populated:?} query={query:?}",
                );
                assert_eq!(
                    b.has_postcondition_kind(query),
                    b.postconditions.has_kind(query),
                    "postcondition arm must delegate to postconditions.has_kind: \
                     populated={populated:?} query={query:?}",
                );
            }
        }
    }

    // ── ConditionSliceExt::find_kind substrate pins + widened triad ──
    //
    // Fail-before-pass-after granularity: `ConditionSliceExt::find_kind`
    // + its three struct-level peers (`Boundary::find_(pre|post)?
    // condition_kind`) did not exist before this commit — the existing
    // `has_*_kind` triad collapses the return to `bool`, losing the
    // matching `&Condition` a future diagnostic consumer (an operator-
    // facing "found on {pre|post}conditions at param.probeImage=X"
    // message, a coherence check verifying "every ClosedLoopAuth
    // postcondition carries a non-empty probeImage", an editor
    // completion listing params-keys per present kind) needs. The lift
    // widens the primitive to `Option<&Condition>` and re-anchors
    // `has_kind` as a default composed from it, so the two refinements
    // share ONE walk semantics by construction.

    /// EMPTY-SLICE pin — an empty `&[Condition]` returns `None` from
    /// `find_kind` for EVERY [`ConditionKind`]. Sweep
    /// `ConditionKind::ALL` so a new variant added without a matching
    /// arm in the primitive surfaces at rustc's exhaustiveness gate on
    /// the ALL literal (arity forced by `[Self; 8]`) rather than as a
    /// silent false-`Some` at every downstream widened callsite.
    #[test]
    fn condition_slice_find_kind_returns_none_on_empty_slice_for_every_kind() {
        let empty: &[Condition] = &[];
        for kind in ConditionKind::ALL {
            assert!(
                empty.find_kind(kind).is_none(),
                "empty slice must return None for {kind:?}",
            );
        }
    }

    /// PER-VARIANT pin — a single-element slice returns `Some` with
    /// the matching kind for exactly the kind it carries, `None` for
    /// every other variant. Sweep the ALL × ALL cross so a regression
    /// that (a) hard-coded the arm to a single kind (silently returning
    /// `Some` for every populated slice regardless of query kind), or
    /// (b) matched on [`Condition::params`] instead of [`Condition::kind`]
    /// fails HERE at the substrate primitive.
    #[test]
    fn condition_slice_find_kind_reads_kind_field_per_variant() {
        for populated in ConditionKind::ALL {
            let slice = [condition_with(populated)];
            for query in ConditionKind::ALL {
                let hit = slice.find_kind(query);
                if query == populated {
                    assert_eq!(
                        hit.map(|c| c.kind),
                        Some(populated),
                        "populated={populated:?}: query {query:?} must return Some",
                    );
                } else {
                    assert!(
                        hit.is_none(),
                        "populated={populated:?}: query {query:?} must return None",
                    );
                }
            }
        }
    }

    /// FIRST-MATCH pin — a slice with the same kind at MULTIPLE
    /// positions returns the earliest by position. Locks the `.iter().
    /// find(...)` semantics so a regression that collapsed to a
    /// `.last()` walk (returning the trailing match) or a `.rev().
    /// find(...)` walk (returning the last-inserted match) surfaces
    /// HERE, since diagnostic consumers reading `find_kind(K).unwrap().
    /// params` expect the FIRST occurrence's params-payload not the
    /// last.
    #[test]
    fn condition_slice_find_kind_returns_first_position_on_duplicate_kinds() {
        // Two ClosedLoopAuth entries with distinct params — a first-
        // match walk resolves to the leading entry's params-payload.
        let first = Condition {
            kind: ConditionKind::ClosedLoopAuth,
            params: json!({ "probeImage": "first" }),
        };
        let second = Condition {
            kind: ConditionKind::ClosedLoopAuth,
            params: json!({ "probeImage": "second" }),
        };
        let slice = [first, second];
        let hit = slice
            .find_kind(ConditionKind::ClosedLoopAuth)
            .expect("populated slice must resolve Some on the matching kind");
        assert_eq!(
            hit.params
                .get("probeImage")
                .and_then(serde_json::Value::as_str),
            Some("first"),
            "find_kind must return the FIRST position's Condition on duplicate kinds",
        );
    }

    /// SLICE-LEVEL DELEGATION pin (has ↔ find) — [`ConditionSliceExt::has_kind`]
    /// equals `find_kind(k).is_some()` at EVERY (populated arrangement,
    /// query) pair on `ConditionKind::ALL`. Turns the trait doc's
    /// "compounding" note ("the closed-set discriminator case becomes
    /// `has_kind(k) == self.find_kind(k).is_some()` by construction")
    /// into a first-class typed test invariant: a future consumer
    /// that overrode the default `has_kind` body with a divergent walk
    /// shape (a `.iter().any(...)` that missed a variant, a `.count() >
    /// 0` predicate on a filtered clone) surfaces HERE at the substrate
    /// boundary rather than as silent skew between the two refinements
    /// downstream consumers reach through.
    #[test]
    fn condition_slice_has_kind_equals_find_kind_is_some() {
        for pre_kind in ConditionKind::ALL {
            for post_kind in ConditionKind::ALL {
                let slice = [condition_with(pre_kind), condition_with(post_kind)];
                for query in ConditionKind::ALL {
                    assert_eq!(
                        slice.has_kind(query),
                        slice.find_kind(query).is_some(),
                        "slice-level has/find refinement bridge drifted: \
                         pre={pre_kind:?} post={post_kind:?} query={query:?}",
                    );
                }
            }
        }
    }

    /// SUBSTRATE-DELEGATION pin (find-triad) — the three widened
    /// `find_*_kind` methods on [`Boundary`] delegate verbatim to
    /// [`ConditionSliceExt::find_kind`] on the underlying
    /// [`Vec<Condition>`] slices, no inline reimplementation. The
    /// `find_condition_kind` union walks preconditions first then
    /// postconditions via `Option::or_else`. Sweep
    /// `ConditionKind::ALL × ConditionKind::ALL × ConditionKind::ALL`
    /// so a regression that (a) inlined a divergent walk at either
    /// half-slice arm, (b) reversed the union walk order (postcondition
    /// first), or (c) collapsed `or_else` to `and_then` (silently
    /// narrowing the union to an intersection) surfaces HERE at the
    /// substrate boundary rather than as silent skew between the
    /// struct-level widened arms and the slice-level primitive.
    #[test]
    fn find_condition_kind_triad_delegates_to_slice_find_kind() {
        for pre_kind in ConditionKind::ALL {
            for post_kind in ConditionKind::ALL {
                let mut b = Boundary::default();
                b.preconditions.push(condition_with(pre_kind));
                b.postconditions.push(condition_with(post_kind));
                for query in ConditionKind::ALL {
                    let via_pre = b.preconditions.find_kind(query);
                    let via_post = b.postconditions.find_kind(query);
                    assert_eq!(
                        b.find_precondition_kind(query).map(|c| c.kind),
                        via_pre.map(|c| c.kind),
                        "precondition find arm must delegate to preconditions.find_kind: \
                         pre={pre_kind:?} post={post_kind:?} query={query:?}",
                    );
                    assert_eq!(
                        b.find_postcondition_kind(query).map(|c| c.kind),
                        via_post.map(|c| c.kind),
                        "postcondition find arm must delegate to postconditions.find_kind: \
                         pre={pre_kind:?} post={post_kind:?} query={query:?}",
                    );
                    let expected_union = via_pre.or(via_post).map(|c| c.kind);
                    assert_eq!(
                        b.find_condition_kind(query).map(|c| c.kind),
                        expected_union,
                        "union find arm must equal precondition.or_else(postcondition): \
                         pre={pre_kind:?} post={post_kind:?} query={query:?}",
                    );
                }
            }
        }
    }

    /// PRECONDITION-PRECEDENCE pin — a kind authored on BOTH sides
    /// returns the precondition-side [`Condition`] from
    /// `find_condition_kind`. Uses two params-distinguishable
    /// [`Condition`]s so a regression that reversed the walk order
    /// (postcondition first) surfaces at the returned params payload
    /// rather than silently at the presence bit (which is `true` on
    /// both walk orders).
    #[test]
    fn find_condition_kind_returns_precondition_side_on_dual_populated() {
        let mut b = Boundary::default();
        b.preconditions.push(Condition {
            kind: ConditionKind::ClosedLoopAuth,
            params: json!({ "side": "pre" }),
        });
        b.postconditions.push(Condition {
            kind: ConditionKind::ClosedLoopAuth,
            params: json!({ "side": "post" }),
        });
        let hit = b
            .find_condition_kind(ConditionKind::ClosedLoopAuth)
            .expect("dual-populated boundary must resolve Some");
        assert_eq!(
            hit.params.get("side").and_then(serde_json::Value::as_str),
            Some("pre"),
            "find_condition_kind must walk preconditions first: dual-populated kind \
             returned postcondition-side Condition rather than precondition-side",
        );
    }

    /// STRUCT-LEVEL DELEGATION pin (has ↔ find) — the three
    /// [`Boundary`] `has_*_kind` arms equal their widened peers'
    /// `.is_some()` projection at EVERY (pre-populated, post-populated,
    /// query) triple on `ConditionKind::ALL`. The three widened
    /// `find_*_kind` arms are the load-bearing primitives; the three
    /// `has_*_kind` arms are their bool projections. Byte-for-byte
    /// re-anchors the composition-law pin
    /// `boundary_has_condition_kind_composes_precondition_and_postcondition_arms`
    /// through the widened axis so a future consumer that reads
    /// `has_condition_kind` as sugar for `find_condition_kind(k).
    /// is_some()` (rather than as `has_precondition_kind ||
    /// has_postcondition_kind`) stays typed against the SAME truth
    /// table.
    #[test]
    fn boundary_has_triad_equals_find_triad_is_some_projection() {
        for pre_kind in ConditionKind::ALL {
            for post_kind in ConditionKind::ALL {
                let mut b = Boundary::default();
                b.preconditions.push(condition_with(pre_kind));
                b.postconditions.push(condition_with(post_kind));
                for query in ConditionKind::ALL {
                    assert_eq!(
                        b.has_precondition_kind(query),
                        b.find_precondition_kind(query).is_some(),
                        "precondition has/find bridge drifted: \
                         pre={pre_kind:?} post={post_kind:?} query={query:?}",
                    );
                    assert_eq!(
                        b.has_postcondition_kind(query),
                        b.find_postcondition_kind(query).is_some(),
                        "postcondition has/find bridge drifted: \
                         pre={pre_kind:?} post={post_kind:?} query={query:?}",
                    );
                    assert_eq!(
                        b.has_condition_kind(query),
                        b.find_condition_kind(query).is_some(),
                        "union has/find bridge drifted: \
                         pre={pre_kind:?} post={post_kind:?} query={query:?}",
                    );
                }
            }
        }
    }

    // ── ConditionSliceExt::iter_kind substrate pins + widened triad ──
    //
    // Fail-before-pass-after granularity: `ConditionSliceExt::iter_kind`
    // + its three struct-level peers (`Boundary::iter_(pre|post|)?
    // condition_kind`) did not exist before this commit — the existing
    // `find_*_kind` triad collapses the return to `Option<&Condition>`
    // (yielding only the FIRST match), losing the full match stream a
    // future coherence check ("each ConditionKind appears at most
    // once per side" — `iter_kind(k).nth(1).is_none()`) or diagnostic
    // consumer ("N ClosedLoopAuth postconditions matched, listing
    // every param.probeImage" — `iter_kind(k).collect()`) needs. The
    // lift widens the primitive to `KindMatches<'_>` (a named
    // Iterator<Item = &Condition>) and re-anchors `find_kind` as a
    // default composed from it (`self.iter_kind(kind).next()`), so
    // the three refinements share ONE walk semantics by construction.

    /// EMPTY-SLICE pin (iter) — an empty `&[Condition]` yields
    /// nothing from `iter_kind` for EVERY [`ConditionKind`]. Sweep
    /// `ConditionKind::ALL` so a new variant added without a matching
    /// arm in the primitive surfaces at rustc's exhaustiveness gate
    /// on the ALL literal rather than as a silent phantom-yield at
    /// every downstream widened callsite.
    #[test]
    fn condition_slice_iter_kind_yields_nothing_on_empty_slice_for_every_kind() {
        let empty: &[Condition] = &[];
        for kind in ConditionKind::ALL {
            assert_eq!(
                empty.iter_kind(kind).count(),
                0,
                "empty slice must yield nothing on iter_kind for {kind:?}",
            );
        }
    }

    /// PER-VARIANT pin (iter) — a single-element slice yields exactly
    /// that element on the matching kind and nothing on every other
    /// kind. Sweep the ALL × ALL cross so a regression that (a)
    /// hard-coded the filter predicate to a single kind (silently
    /// yielding on every populated slice regardless of query kind),
    /// or (b) matched on [`Condition::params`] instead of
    /// [`Condition::kind`] fails HERE at the substrate primitive.
    #[test]
    fn condition_slice_iter_kind_reads_kind_field_per_variant() {
        for populated in ConditionKind::ALL {
            let slice = [condition_with(populated)];
            for query in ConditionKind::ALL {
                let collected: Vec<_> = slice.iter_kind(query).map(|c| c.kind).collect();
                if query == populated {
                    assert_eq!(
                        collected,
                        vec![populated],
                        "populated={populated:?}: query {query:?} must yield [populated]",
                    );
                } else {
                    assert!(
                        collected.is_empty(),
                        "populated={populated:?}: query {query:?} must yield nothing",
                    );
                }
            }
        }
    }

    /// ALL-MATCHES pin — a slice with the same kind at MULTIPLE
    /// positions yields EVERY match in slice order (not just the
    /// first). Uses params-distinguishable [`Condition`]s so a
    /// regression that (a) collapsed to a single-match walk
    /// (`.iter().find(...)` yielding only the earliest and
    /// terminating), (b) reversed the yield order (`.rev().filter`
    /// yielding trailing-first), or (c) de-duplicated by kind (an
    /// erroneous `HashSet::insert`-gated walk) surfaces HERE at the
    /// params payload rather than silently at a downstream
    /// count-based coherence check.
    #[test]
    fn condition_slice_iter_kind_yields_every_match_in_slice_order_on_duplicates() {
        let first = Condition {
            kind: ConditionKind::ClosedLoopAuth,
            params: json!({ "probeImage": "first" }),
        };
        let middle = Condition {
            kind: ConditionKind::PromQL,
            params: json!({ "query": "up" }),
        };
        let second_cla = Condition {
            kind: ConditionKind::ClosedLoopAuth,
            params: json!({ "probeImage": "second" }),
        };
        let slice = [first, middle, second_cla];
        let hits: Vec<_> = slice
            .iter_kind(ConditionKind::ClosedLoopAuth)
            .map(|c| {
                c.params
                    .get("probeImage")
                    .and_then(serde_json::Value::as_str)
                    .unwrap_or_default()
                    .to_owned()
            })
            .collect();
        assert_eq!(
            hits,
            vec!["first".to_owned(), "second".to_owned()],
            "iter_kind must yield every match in slice order (not just the first)",
        );
        // The interleaved non-matching kind is skipped: two hits, not three.
        assert_eq!(
            slice.iter_kind(ConditionKind::ClosedLoopAuth).count(),
            2,
            "iter_kind must skip non-matching kinds, not include them in the stream",
        );
    }

    /// SLICE-LEVEL DELEGATION pin (find ↔ iter) — the trait's default
    /// `find_kind` body equals `iter_kind(k).next()` at EVERY
    /// (populated arrangement, query) pair on `ConditionKind::ALL`.
    /// Turns the trait doc's composition-law note
    /// ("`find_kind(k) == iter_kind(k).next()` by construction")
    /// into a first-class typed test invariant: a future implementor
    /// that overrode the default `find_kind` body with a divergent
    /// walk shape (a `.iter().rev().find(...)` returning trailing-
    /// first, a hand-rolled loop that walked past the first match)
    /// surfaces HERE at the substrate boundary rather than as silent
    /// skew between the two refinements downstream consumers reach
    /// through.
    #[test]
    fn condition_slice_find_kind_equals_iter_kind_next() {
        for pre_kind in ConditionKind::ALL {
            for post_kind in ConditionKind::ALL {
                let slice = [condition_with(pre_kind), condition_with(post_kind)];
                for query in ConditionKind::ALL {
                    assert_eq!(
                        slice.find_kind(query).map(|c| c.kind),
                        slice.iter_kind(query).next().map(|c| c.kind),
                        "slice-level find/iter refinement bridge drifted: \
                         pre={pre_kind:?} post={post_kind:?} query={query:?}",
                    );
                }
            }
        }
    }

    /// SUBSTRATE-DELEGATION pin (Boundary iter-triad) — the three
    /// widened `iter_*_kind` methods on [`Boundary`] delegate verbatim
    /// to [`ConditionSliceExt::iter_kind`] on the underlying
    /// [`Vec<Condition>`] slices, no inline reimplementation. The
    /// `iter_condition_kind` union chains preconditions first then
    /// postconditions via [`Iterator::chain`]. Sweep
    /// `ConditionKind::ALL × ConditionKind::ALL × ConditionKind::ALL`
    /// so a regression that (a) inlined a divergent walk at either
    /// half-slice arm, (b) reversed the chain order (postcondition
    /// first — walk-order regression on the union), or (c) collapsed
    /// the chain to a `.zip(...)` (silently narrowing the union to
    /// an intersection-by-position) surfaces HERE at the substrate
    /// boundary rather than as silent skew between the struct-level
    /// widened arms and the slice-level primitive.
    #[test]
    fn iter_condition_kind_triad_delegates_to_slice_iter_kind() {
        for pre_kind in ConditionKind::ALL {
            for post_kind in ConditionKind::ALL {
                let mut b = Boundary::default();
                b.preconditions.push(condition_with(pre_kind));
                b.postconditions.push(condition_with(post_kind));
                for query in ConditionKind::ALL {
                    let via_pre: Vec<_> =
                        b.preconditions.iter_kind(query).map(|c| c.kind).collect();
                    let via_post: Vec<_> =
                        b.postconditions.iter_kind(query).map(|c| c.kind).collect();
                    assert_eq!(
                        b.iter_precondition_kind(query)
                            .map(|c| c.kind)
                            .collect::<Vec<_>>(),
                        via_pre,
                        "precondition iter arm must delegate to preconditions.iter_kind: \
                         pre={pre_kind:?} post={post_kind:?} query={query:?}",
                    );
                    assert_eq!(
                        b.iter_postcondition_kind(query)
                            .map(|c| c.kind)
                            .collect::<Vec<_>>(),
                        via_post,
                        "postcondition iter arm must delegate to postconditions.iter_kind: \
                         pre={pre_kind:?} post={post_kind:?} query={query:?}",
                    );
                    let mut expected_union = via_pre.clone();
                    expected_union.extend(via_post.iter().copied());
                    assert_eq!(
                        b.iter_condition_kind(query)
                            .map(|c| c.kind)
                            .collect::<Vec<_>>(),
                        expected_union,
                        "union iter arm must chain precondition ⨟ postcondition: \
                         pre={pre_kind:?} post={post_kind:?} query={query:?}",
                    );
                }
            }
        }
    }

    /// STRUCT-LEVEL DELEGATION pin (find ↔ iter on Boundary) — the
    /// three [`Boundary`] `find_*_kind` arms equal their widened
    /// peers' `.next()` projection at EVERY (pre-populated,
    /// post-populated, query) triple on `ConditionKind::ALL`. Byte-
    /// for-byte re-anchors the composition-law pin
    /// `find_condition_kind == iter_condition_kind.next()` through
    /// the widened axis on the parent surface — a future consumer
    /// that reads `find_condition_kind(k)` as sugar for
    /// `iter_condition_kind(k).next()` stays typed against the SAME
    /// truth table on both the slice-level and struct-level layers.
    #[test]
    fn boundary_find_triad_equals_iter_triad_next_projection() {
        for pre_kind in ConditionKind::ALL {
            for post_kind in ConditionKind::ALL {
                let mut b = Boundary::default();
                b.preconditions.push(condition_with(pre_kind));
                b.postconditions.push(condition_with(post_kind));
                for query in ConditionKind::ALL {
                    assert_eq!(
                        b.find_precondition_kind(query).map(|c| c.kind),
                        b.iter_precondition_kind(query).next().map(|c| c.kind),
                        "precondition find/iter bridge drifted: \
                         pre={pre_kind:?} post={post_kind:?} query={query:?}",
                    );
                    assert_eq!(
                        b.find_postcondition_kind(query).map(|c| c.kind),
                        b.iter_postcondition_kind(query).next().map(|c| c.kind),
                        "postcondition find/iter bridge drifted: \
                         pre={pre_kind:?} post={post_kind:?} query={query:?}",
                    );
                    assert_eq!(
                        b.find_condition_kind(query).map(|c| c.kind),
                        b.iter_condition_kind(query).next().map(|c| c.kind),
                        "union find/iter bridge drifted: \
                         pre={pre_kind:?} post={post_kind:?} query={query:?}",
                    );
                }
            }
        }
    }

    /// PRECONDITION-PRECEDENCE pin (iter) — a kind authored on BOTH
    /// sides yields precondition-side matches FIRST in the union
    /// chain. Uses params-distinguishable [`Condition`]s so a
    /// regression that (a) reversed the chain order on the widened
    /// axis (postcondition first), (b) interleaved the two sides,
    /// or (c) collapsed the chain to a `.zip(...)` fails at the
    /// returned params-payload sequence rather than silently at the
    /// count.
    #[test]
    fn iter_condition_kind_yields_preconditions_before_postconditions_on_dual_populated() {
        let mut b = Boundary::default();
        b.preconditions.push(Condition {
            kind: ConditionKind::ClosedLoopAuth,
            params: json!({ "side": "pre-1" }),
        });
        b.preconditions.push(Condition {
            kind: ConditionKind::ClosedLoopAuth,
            params: json!({ "side": "pre-2" }),
        });
        b.postconditions.push(Condition {
            kind: ConditionKind::ClosedLoopAuth,
            params: json!({ "side": "post-1" }),
        });
        let sides: Vec<_> = b
            .iter_condition_kind(ConditionKind::ClosedLoopAuth)
            .map(|c| {
                c.params
                    .get("side")
                    .and_then(serde_json::Value::as_str)
                    .unwrap_or_default()
                    .to_owned()
            })
            .collect();
        assert_eq!(
            sides,
            vec!["pre-1".to_owned(), "pre-2".to_owned(), "post-1".to_owned(),],
            "iter_condition_kind must yield every precondition-side match before any \
             postcondition-side match (chain order pinned by two-surface parity contract)",
        );
    }

    // ----- count_kind — scalar cardinality refinement --------------------
    //
    // The `count_kind` fourth refinement collapses the widened
    // `iter_kind` stream to its cardinality without materializing an
    // intermediate `Vec` or `Option`. Distinct composition law from the
    // three prior refinements: `count_condition_kind` SUMS pre + post
    // (rather than OR-ing them via `has`, or_else-ing them via `find`,
    // or Chain-ing them via `iter`). The tests below pin (a) the default
    // trait body against the primitive `iter_kind(k).count()`, (b) the
    // slice-level composition laws `has_kind(k) == (count_kind(k) > 0)`
    // and `find_kind(k).is_some() == (count_kind(k) > 0)`, (c) the
    // struct-level SUM composition on both `Boundary` half-slice arms,
    // and (d) the two-surface parity contract with
    // `EphemeralSpec::count_(pre|post|)condition_kind` (in ephemeral.rs).

    /// EMPTY-SLICE pin (count) — an empty `&[Condition]` returns `0`
    /// from `count_kind` for EVERY [`ConditionKind`]. Sweep
    /// `ConditionKind::ALL` so a new variant added without a matching
    /// arm surfaces at rustc's exhaustiveness gate on the ALL literal
    /// rather than as silent phantom-cardinality at every downstream
    /// count callsite.
    #[test]
    fn condition_slice_count_kind_returns_zero_on_empty_slice_for_every_kind() {
        let empty: &[Condition] = &[];
        for kind in ConditionKind::ALL {
            assert_eq!(
                empty.count_kind(kind),
                0,
                "empty slice must count 0 for {kind:?}",
            );
        }
    }

    /// PER-VARIANT pin (count) — a single-element slice returns `1`
    /// on the matching kind and `0` on every other kind. Sweep ALL ×
    /// ALL so a regression that (a) hard-coded the filter predicate
    /// to a single kind (silently counting every populated slice
    /// regardless of query), or (b) matched on [`Condition::params`]
    /// instead of [`Condition::kind`] fails HERE at the substrate
    /// primitive.
    #[test]
    fn condition_slice_count_kind_reads_kind_field_per_variant() {
        for populated in ConditionKind::ALL {
            let slice = [condition_with(populated)];
            for query in ConditionKind::ALL {
                let expected = if query == populated { 1 } else { 0 };
                assert_eq!(
                    slice.count_kind(query),
                    expected,
                    "populated={populated:?} query={query:?} \
                     must count {expected}",
                );
            }
        }
    }

    /// DUPLICATES pin (count) — a slice with the same kind at
    /// MULTIPLE positions returns the exact match count (not `1`, not
    /// a de-duplicated `1`). A regression that (a) short-circuited on
    /// the first match (an `.iter().find(...)` yielding `0`/`1` sugar
    /// on the count arm), or (b) de-duplicated by kind (an erroneous
    /// `HashSet::insert`-gated walk that swallowed repeats) surfaces
    /// HERE at the cardinality boundary rather than silently at a
    /// downstream count-based coherence check.
    #[test]
    fn condition_slice_count_kind_counts_every_match_on_duplicates() {
        let slice = [
            Condition {
                kind: ConditionKind::ClosedLoopAuth,
                params: json!({ "probeImage": "first" }),
            },
            Condition {
                kind: ConditionKind::PromQL,
                params: json!({ "query": "up" }),
            },
            Condition {
                kind: ConditionKind::ClosedLoopAuth,
                params: json!({ "probeImage": "second" }),
            },
        ];
        assert_eq!(slice.count_kind(ConditionKind::ClosedLoopAuth), 2);
        assert_eq!(slice.count_kind(ConditionKind::PromQL), 1);
        for kind in ConditionKind::ALL {
            if matches!(kind, ConditionKind::ClosedLoopAuth | ConditionKind::PromQL) {
                continue;
            }
            assert_eq!(
                slice.count_kind(kind),
                0,
                "non-populated kind {kind:?} must count 0",
            );
        }
    }

    /// SLICE-LEVEL DELEGATION pin (count ↔ iter) — the trait's
    /// default `count_kind` body equals `iter_kind(k).count()` at
    /// EVERY (populated arrangement, query) pair on
    /// `ConditionKind::ALL`. Turns the trait doc's composition-law
    /// note (`count_kind(k) == iter_kind(k).count()` by construction)
    /// into a first-class typed invariant: a future implementor that
    /// overrode the default `count_kind` body with a divergent walk
    /// shape (a stored-length cache that drifted, a `.step_by(2)`
    /// artefact from a copy-paste of `iter_kind`) surfaces HERE.
    #[test]
    fn condition_slice_count_kind_equals_iter_kind_count() {
        for pre_kind in ConditionKind::ALL {
            for post_kind in ConditionKind::ALL {
                let slice = [condition_with(pre_kind), condition_with(post_kind)];
                for query in ConditionKind::ALL {
                    assert_eq!(
                        slice.count_kind(query),
                        slice.iter_kind(query).count(),
                        "count/iter bridge drifted: pre={pre_kind:?} \
                         post={post_kind:?} query={query:?}",
                    );
                }
            }
        }
    }

    /// SLICE-LEVEL DELEGATION pin (count ↔ has ↔ find) — the two
    /// composition laws
    /// `has_kind(k) == (count_kind(k) > 0)` and
    /// `find_kind(k).is_some() == (count_kind(k) > 0)`
    /// hold at every (populated, populated, query) triple on
    /// `ConditionKind::ALL`. Sweeps both refinement bridges at ONE
    /// site so a regression at the count primitive that drifted from
    /// the presence bit or the first-match probe surfaces HERE.
    #[test]
    fn condition_slice_has_and_find_equal_count_greater_than_zero() {
        for pre_kind in ConditionKind::ALL {
            for post_kind in ConditionKind::ALL {
                let slice = [condition_with(pre_kind), condition_with(post_kind)];
                for query in ConditionKind::ALL {
                    let count = slice.count_kind(query);
                    assert_eq!(
                        slice.has_kind(query),
                        count > 0,
                        "has/count bridge drifted: pre={pre_kind:?} \
                         post={post_kind:?} query={query:?}",
                    );
                    assert_eq!(
                        slice.find_kind(query).is_some(),
                        count > 0,
                        "find/count bridge drifted: pre={pre_kind:?} \
                         post={post_kind:?} query={query:?}",
                    );
                }
            }
        }
    }

    /// SUBSTRATE-DELEGATION pin (Boundary count-triad) — the three
    /// widened `count_*_kind` methods on [`Boundary`] delegate
    /// verbatim to [`ConditionSliceExt::count_kind`] on the
    /// underlying [`Vec<Condition>`] slices. The
    /// `count_condition_kind` union SUMS preconditions and
    /// postconditions (distinct from the `iter_condition_kind`
    /// [`Chain`](std::iter::Chain), `find_condition_kind`
    /// [`Option::or_else`], and `has_condition_kind` `||`
    /// compositions on the same axis). Sweep `ConditionKind::ALL ×
    /// ConditionKind::ALL × ConditionKind::ALL` so a regression that
    /// (a) inlined a divergent count at either half-slice arm, (b)
    /// subtracted rather than summed, or (c) collapsed the sum to
    /// [`std::cmp::max`] (silently narrowing the union to a max-per-
    /// side probe) surfaces HERE at the substrate boundary.
    #[test]
    fn boundary_count_condition_kind_triad_delegates_and_sums_slice_count_kind() {
        for pre_kind in ConditionKind::ALL {
            for post_kind in ConditionKind::ALL {
                let mut b = Boundary::default();
                b.preconditions.push(condition_with(pre_kind));
                b.postconditions.push(condition_with(post_kind));
                for query in ConditionKind::ALL {
                    let via_pre = b.preconditions.count_kind(query);
                    let via_post = b.postconditions.count_kind(query);
                    assert_eq!(
                        b.count_precondition_kind(query),
                        via_pre,
                        "boundary precondition count arm must delegate: \
                         pre={pre_kind:?} post={post_kind:?} query={query:?}",
                    );
                    assert_eq!(
                        b.count_postcondition_kind(query),
                        via_post,
                        "boundary postcondition count arm must delegate: \
                         pre={pre_kind:?} post={post_kind:?} query={query:?}",
                    );
                    assert_eq!(
                        b.count_condition_kind(query),
                        via_pre + via_post,
                        "boundary union count arm must SUM pre + post: \
                         pre={pre_kind:?} post={post_kind:?} query={query:?}",
                    );
                }
            }
        }
    }

    /// STRUCT-LEVEL DELEGATION pin (count ↔ iter on Boundary) — the
    /// three [`Boundary`] `count_*_kind` arms equal their widened
    /// peers' `.count()` projection at EVERY (pre-populated, post-
    /// populated, query) triple on `ConditionKind::ALL`. Re-anchors
    /// the composition-law pin
    /// `count_condition_kind == iter_condition_kind.count()` through
    /// the cardinality axis on the parent surface — a future consumer
    /// that reads `count_condition_kind(k)` as sugar for
    /// `iter_condition_kind(k).count()` stays typed against the SAME
    /// truth table on both the slice-level and struct-level layers.
    /// Also pins the sum-composition round-trip through the widened
    /// stream: the union arm's SUM equals the chained stream's count.
    #[test]
    fn boundary_count_triad_equals_iter_triad_count_projection() {
        for pre_kind in ConditionKind::ALL {
            for post_kind in ConditionKind::ALL {
                let mut b = Boundary::default();
                b.preconditions.push(condition_with(pre_kind));
                b.preconditions.push(condition_with(pre_kind));
                b.postconditions.push(condition_with(post_kind));
                for query in ConditionKind::ALL {
                    assert_eq!(
                        b.count_precondition_kind(query),
                        b.iter_precondition_kind(query).count(),
                        "precondition count/iter bridge drifted: \
                         pre={pre_kind:?} post={post_kind:?} query={query:?}",
                    );
                    assert_eq!(
                        b.count_postcondition_kind(query),
                        b.iter_postcondition_kind(query).count(),
                        "postcondition count/iter bridge drifted: \
                         pre={pre_kind:?} post={post_kind:?} query={query:?}",
                    );
                    assert_eq!(
                        b.count_condition_kind(query),
                        b.iter_condition_kind(query).count(),
                        "union count/iter bridge drifted: \
                         pre={pre_kind:?} post={post_kind:?} query={query:?}",
                    );
                }
            }
        }
    }

    // ── ConditionSliceExt::distinct_kinds — closed-set-inversion axis ──
    //
    // The fifth refinement on the slice-level presence-probe algebra
    // inverts the axis: the four point-probe refinements (has, find,
    // iter, count) fix a [`ConditionKind`] and vary the return type;
    // `distinct_kinds` fixes the slice and varies over
    // [`ConditionKind::ALL`], returning the SET of present kinds
    // projected in [`ConditionKind::ALL`] order with no duplicates.
    // The composition-law arms in `assert_slice_refinement_composition_laws`
    // pin the fifth refinement against `has_kind` per variant AND
    // against the canonical ALL-order equality; the four dedicated
    // behavior tests below pin the returned VALUE per authored
    // arrangement (empty, single-element populated, dual-populated,
    // duplicate-populated).

    /// EMPTY-SLICE pin — an empty slice returns an empty `Vec` on
    /// `distinct_kinds`, distinct from every populated arrangement.
    /// Locks the zero-element identity so a regression that (a)
    /// returned `ConditionKind::ALL.to_vec()` (the wrong direction of
    /// the closed-set walk), (b) returned a placeholder `[ProcessPhase]`
    /// vec (a copy-paste of the first-variant default in a `impl
    /// Default` for a hypothetical `KindSet` wrapper) surfaces HERE.
    #[test]
    fn condition_slice_distinct_kinds_returns_empty_vec_on_empty_slice() {
        let empty: &[Condition] = &[];
        assert_eq!(
            empty.distinct_kinds(),
            Vec::<ConditionKind>::new(),
            "empty slice must return empty distinct-kinds vec",
        );
    }

    /// PER-VARIANT pin — a slice with EXACTLY ONE `Condition` carrying
    /// the addressed kind returns `[kind]` — a single-element vec
    /// containing exactly that kind. Sweep `ConditionKind::ALL` so a
    /// new variant added without a matching arm in the closed-set walk
    /// surfaces at rustc's exhaustiveness gate on the ALL literal
    /// (arity forced by `[Self; 8]`) rather than as a silent false-
    /// negative at every downstream `distinct_condition_kinds`
    /// callsite. Locks the closed-set-inversion probe body against a
    /// regression that (a) always returned `[ProcessPhase]` regardless
    /// of the actual kind, (b) collapsed `distinct_kinds` to
    /// `iter_kind(<first ALL variant>).map(|c| c.kind).collect()`
    /// (silently filtering to only ProcessPhase matches).
    #[test]
    fn condition_slice_distinct_kinds_returns_single_element_vec_per_variant() {
        for populated in ConditionKind::ALL {
            let slice = [condition_with(populated)];
            assert_eq!(
                slice.distinct_kinds(),
                vec![populated],
                "single-populated slice must return exactly [{populated:?}] on distinct_kinds",
            );
        }
    }

    /// DEDUP pin — a slice with the SAME kind at multiple positions
    /// (three interleaved with distinct kinds) returns a distinct-set
    /// containing that kind exactly ONCE. The closed-set-inversion
    /// projection collapses multiplicity — a caller that needs the
    /// per-kind cardinality reaches for `count_kind`; this refinement
    /// returns the PRESENCE set. A regression that (a) omitted the
    /// dedup and returned `[ClosedLoopAuth, PromQL, ClosedLoopAuth,
    /// PromQL, ClosedLoopAuth]` (byte-identical to
    /// `slice.iter().map(|c| c.kind).collect()` — the wrong closed-
    /// set walk direction), (b) counted every duplicate as a distinct
    /// entry via a `.collect::<HashSet<_>>()` without canonicalizing
    /// order surfaces HERE.
    #[test]
    fn condition_slice_distinct_kinds_deduplicates_and_yields_canonical_all_order() {
        let interleaved = [
            Condition {
                kind: ConditionKind::ClosedLoopAuth,
                params: json!({ "probeImage": "first" }),
            },
            Condition {
                kind: ConditionKind::PromQL,
                params: json!({ "query": "up" }),
            },
            Condition {
                kind: ConditionKind::ClosedLoopAuth,
                params: json!({ "probeImage": "second" }),
            },
            Condition {
                kind: ConditionKind::PromQL,
                params: json!({ "query": "healthy" }),
            },
            Condition {
                kind: ConditionKind::ClosedLoopAuth,
                params: json!({ "probeImage": "third" }),
            },
        ];
        // Canonical ConditionKind::ALL order: PromQL is at position 3,
        // ClosedLoopAuth at position 7 in the ALL array. So PromQL comes
        // FIRST in the distinct-set even though ClosedLoopAuth appears
        // FIRST in the slice — the closed-set-inversion walk is
        // ordered by ConditionKind::ALL, not by slice-encounter order.
        assert_eq!(
            interleaved.distinct_kinds(),
            vec![ConditionKind::PromQL, ConditionKind::ClosedLoopAuth],
            "interleaved-duplicate slice must dedup AND order by ConditionKind::ALL, not by slice-encounter order",
        );
    }

    /// FULL-COVERAGE pin — a slice that carries every [`ConditionKind`]
    /// variant returns `ConditionKind::ALL.to_vec()` on `distinct_kinds`.
    /// The closed-set-inversion probe covers the full closed set at ONE
    /// call site — a regression that missed one variant in the walk
    /// (skipping the FIRST or LAST `ALL` entry via a `[1..]` or
    /// `[..ALL.len() - 1]` slice bug in the closed-set walk) surfaces
    /// HERE.
    #[test]
    fn condition_slice_distinct_kinds_covers_full_closed_set_on_saturated_slice() {
        let saturated: Vec<Condition> =
            ConditionKind::ALL.into_iter().map(condition_with).collect();
        assert_eq!(
            saturated.as_slice().distinct_kinds(),
            ConditionKind::ALL.to_vec(),
            "slice containing every ConditionKind must return ConditionKind::ALL as its distinct-set",
        );
    }

    // ── distinct_kind_count — slice-level scalar-cardinality pins ──────
    //
    // The trait-level scalar-cardinality projection of the closed-set-
    // inversion widened primitive: `distinct_kind_count()` collapses
    // `distinct_kinds()` to its cardinality without materializing the
    // intermediate `Vec<ConditionKind>`. Composition law
    // `distinct_kind_count() == distinct_kinds().len()` pinned as the
    // sixth arm of the substrate testkit primitive
    // [`assert_slice_refinement_composition_laws`].

    /// ZERO-ELEMENT pin — an empty slice returns `0` on
    /// `distinct_kind_count`, byte-for-byte with `distinct_kinds().len()`
    /// on the same slice. Locks the zero-element identity so a
    /// regression that (a) returned `ConditionKind::ALL.len()` (the
    /// wrong direction of the closed-set walk — every kind counted
    /// regardless of presence), (b) returned a placeholder `1` (a
    /// copy-paste of a single-slot factory's cardinality), or (c) drifted
    /// off `distinct_kinds().len()` surfaces HERE.
    #[test]
    fn condition_slice_distinct_kind_count_returns_zero_on_empty_slice() {
        let empty: &[Condition] = &[];
        assert_eq!(
            empty.distinct_kind_count(),
            0,
            "empty slice must return 0 on distinct_kind_count",
        );
        assert_eq!(
            empty.distinct_kind_count(),
            empty.distinct_kinds().len(),
            "empty slice distinct_kind_count must equal distinct_kinds().len()",
        );
    }

    /// PER-VARIANT pin — a slice with EXACTLY ONE `Condition` carrying
    /// the addressed kind returns `1` on `distinct_kind_count` — the
    /// single-slot diagonal cardinality. Sweep [`ConditionKind::ALL`]
    /// so a regression that (a) always returned `0` regardless of the
    /// actual kind, (b) always returned `ConditionKind::ALL.len()`
    /// (missed the `filter` step), or (c) collapsed the walk to a
    /// single fixed variant surfaces HERE.
    #[test]
    fn condition_slice_distinct_kind_count_returns_one_per_variant() {
        for populated in ConditionKind::ALL {
            let slice = [condition_with(populated)];
            assert_eq!(
                slice.distinct_kind_count(),
                1,
                "single-populated slice must return 1 on distinct_kind_count for {populated:?}",
            );
            assert_eq!(
                slice.distinct_kind_count(),
                slice.distinct_kinds().len(),
                "single-populated distinct_kind_count must equal distinct_kinds().len() for {populated:?}",
            );
        }
    }

    /// DEDUP pin — a slice with the SAME kind at multiple positions
    /// (three interleaved with distinct kinds — two `PromQL`, three
    /// `ClosedLoopAuth`) returns `2` on `distinct_kind_count` (the
    /// scalar cardinality of the DISTINCT presence set, byte-for-byte
    /// with `distinct_kinds().len()` on the same slice). Locks the
    /// closed-set projection against a regression that (a) counted
    /// every occurrence (returning `5` — byte-identical to
    /// `slice.len()`), (b) omitted the dedup and returned `5` via
    /// `.iter().map(|c| c.kind).count()`.
    #[test]
    fn condition_slice_distinct_kind_count_dedups_across_duplicates() {
        let interleaved = [
            Condition {
                kind: ConditionKind::ClosedLoopAuth,
                params: json!({ "probeImage": "first" }),
            },
            Condition {
                kind: ConditionKind::PromQL,
                params: json!({ "query": "up" }),
            },
            Condition {
                kind: ConditionKind::ClosedLoopAuth,
                params: json!({ "probeImage": "second" }),
            },
            Condition {
                kind: ConditionKind::PromQL,
                params: json!({ "query": "healthy" }),
            },
            Condition {
                kind: ConditionKind::ClosedLoopAuth,
                params: json!({ "probeImage": "third" }),
            },
        ];
        assert_eq!(
            interleaved.distinct_kind_count(),
            2,
            "interleaved-duplicate slice must return 2 on distinct_kind_count (PromQL + ClosedLoopAuth)",
        );
        assert_eq!(
            interleaved.distinct_kind_count(),
            interleaved.distinct_kinds().len(),
            "interleaved-duplicate distinct_kind_count must equal distinct_kinds().len()",
        );
    }

    /// FULL-COVERAGE pin — a slice that carries every [`ConditionKind`]
    /// variant returns `ConditionKind::ALL.len()` on `distinct_kind_count`.
    /// The scalar cardinality projection covers the full closed set at
    /// ONE call site — a regression that missed one variant in the walk
    /// (skipping the FIRST or LAST `ALL` entry via a `[1..]` or
    /// `[..ALL.len() - 1]` slice bug in the closed-set walk) surfaces
    /// HERE.
    #[test]
    fn condition_slice_distinct_kind_count_covers_full_closed_set_on_saturated_slice() {
        let saturated: Vec<Condition> =
            ConditionKind::ALL.into_iter().map(condition_with).collect();
        assert_eq!(
            saturated.as_slice().distinct_kind_count(),
            ConditionKind::ALL.len(),
            "slice containing every ConditionKind must return ConditionKind::ALL.len() on distinct_kind_count",
        );
        assert_eq!(
            saturated.as_slice().distinct_kind_count(),
            saturated.as_slice().distinct_kinds().len(),
            "saturated distinct_kind_count must equal distinct_kinds().len()",
        );
    }

    // ── ConditionSliceExt::missing_kinds — closed-set-complement axis ──
    //
    // The complement peer of `distinct_kinds` on the closed-set-
    // inversion axis: `missing_kinds` returns the SET of kinds that
    // do NOT appear in the slice, in canonical [`ConditionKind::ALL`]
    // order. The four tests below pin each authored arrangement's
    // returned VALUE (empty, single-populated, saturated, interleaved-
    // duplicate); the composition-law arms in
    // `assert_slice_refinement_composition_laws` pin the closed-set-
    // partition invariants against `distinct_kinds` and `has_kind`.

    /// EMPTY-SLICE pin — an empty slice returns
    /// `ConditionKind::ALL.to_vec()` on `missing_kinds` (every kind is
    /// missing). Locks the maximum-cardinality identity on the
    /// complement side, byte-for-byte dual to the empty-slice arm of
    /// `distinct_kinds` (which returns an empty vec). A regression that
    /// returned an empty vec (forgot the negation) or a placeholder
    /// `[ProcessPhase]` (a copy-paste of the first-variant default)
    /// surfaces HERE.
    #[test]
    fn condition_slice_missing_kinds_returns_full_closed_set_on_empty_slice() {
        let empty: &[Condition] = &[];
        assert_eq!(
            empty.missing_kinds(),
            ConditionKind::ALL.to_vec(),
            "empty slice must return ConditionKind::ALL on missing_kinds (every kind is missing)",
        );
    }

    /// PER-VARIANT pin — a slice with EXACTLY ONE `Condition` carrying
    /// the addressed kind returns `ConditionKind::ALL` MINUS that kind
    /// on `missing_kinds`. Sweep [`ConditionKind::ALL`] so a regression
    /// that (a) returned an empty vec regardless of the kind, (b)
    /// returned the full ALL vec (forgot to filter), or (c) inverted
    /// the negation and returned only the addressed kind surfaces HERE.
    #[test]
    fn condition_slice_missing_kinds_returns_all_minus_populated_kind() {
        for populated in ConditionKind::ALL {
            let slice = [condition_with(populated)];
            let expected: Vec<_> = ConditionKind::ALL
                .into_iter()
                .filter(|k| *k != populated)
                .collect();
            assert_eq!(
                slice.missing_kinds(),
                expected,
                "single-populated slice must return ConditionKind::ALL minus {populated:?} on missing_kinds",
            );
        }
    }

    /// FULL-COVERAGE pin — a slice that carries every [`ConditionKind`]
    /// variant returns an empty vec on `missing_kinds` (no kind is
    /// missing). Dual of the empty-slice arm above; a regression that
    /// returned the full ALL vec regardless of population or inverted
    /// the presence direction surfaces HERE.
    #[test]
    fn condition_slice_missing_kinds_returns_empty_vec_on_saturated_slice() {
        let saturated: Vec<Condition> =
            ConditionKind::ALL.into_iter().map(condition_with).collect();
        assert_eq!(
            saturated.as_slice().missing_kinds(),
            Vec::<ConditionKind>::new(),
            "slice containing every ConditionKind must return empty vec on missing_kinds",
        );
    }

    /// DEDUP pin — a slice with the SAME kind at multiple positions
    /// (three ClosedLoopAuth, two PromQL, none of the other six)
    /// returns those SIX absent kinds on `missing_kinds`, in canonical
    /// [`ConditionKind::ALL`] order — multiplicity on the present side
    /// is irrelevant to the complement. A regression that (a) counted
    /// duplicates as decreasing the missing set (a `saturating_sub`
    /// bug in a cardinality-tracking override), (b) yielded the
    /// missing set in slice-encounter order (which is undefined when
    /// no positions carry the missing kind — a subtle failure mode
    /// that must yield the ALL-ordered subsequence regardless)
    /// surfaces HERE.
    #[test]
    fn condition_slice_missing_kinds_yields_canonical_all_order_on_duplicates() {
        let interleaved = [
            Condition {
                kind: ConditionKind::ClosedLoopAuth,
                params: json!({ "probeImage": "first" }),
            },
            Condition {
                kind: ConditionKind::PromQL,
                params: json!({ "query": "up" }),
            },
            Condition {
                kind: ConditionKind::ClosedLoopAuth,
                params: json!({ "probeImage": "second" }),
            },
            Condition {
                kind: ConditionKind::PromQL,
                params: json!({ "query": "healthy" }),
            },
            Condition {
                kind: ConditionKind::ClosedLoopAuth,
                params: json!({ "probeImage": "third" }),
            },
        ];
        let expected: Vec<_> = ConditionKind::ALL
            .into_iter()
            .filter(|k| *k != ConditionKind::PromQL && *k != ConditionKind::ClosedLoopAuth)
            .collect();
        assert_eq!(
            interleaved.missing_kinds(),
            expected,
            "interleaved-duplicate slice must return canonical ALL-ordered complement of {{PromQL, ClosedLoopAuth}}",
        );
    }

    // ── ConditionSliceExt::missing_kind_count — scalar cardinality pins ─
    //
    // Scalar-cardinality peer of the closed-set-complement widened
    // primitive `missing_kinds`: `missing_kind_count()` collapses the
    // set to its cardinality without allocating. The composition law
    // `missing_kind_count() == missing_kinds().len()` is pinned as the
    // scalar-cardinality-complement arm of
    // `assert_slice_refinement_composition_laws`. The three tests below
    // pin each authored arrangement's returned VALUE (empty, single-
    // populated, saturated) directly against `missing_kinds().len()`.

    /// EMPTY-SLICE pin — an empty slice returns
    /// `ConditionKind::ALL.len()` on `missing_kind_count`, byte-for-byte
    /// with `missing_kinds().len()`. Locks the maximum-cardinality
    /// identity on the complement side; dual of the empty-slice arm on
    /// `distinct_kind_count` which returns `0`. A regression that
    /// forgot the negation, returned `0` (the distinct-kind-count
    /// identity on empty), or returned the wrong constant surfaces
    /// HERE.
    #[test]
    fn condition_slice_missing_kind_count_returns_full_closed_set_on_empty_slice() {
        let empty: &[Condition] = &[];
        assert_eq!(
            empty.missing_kind_count(),
            ConditionKind::ALL.len(),
            "empty slice must return ConditionKind::ALL.len() on missing_kind_count",
        );
        assert_eq!(
            empty.missing_kind_count(),
            empty.missing_kinds().len(),
            "empty slice missing_kind_count must equal missing_kinds().len()",
        );
    }

    /// PER-VARIANT pin — a slice with EXACTLY ONE `Condition` carrying
    /// the addressed kind returns `ConditionKind::ALL.len() - 1` on
    /// `missing_kind_count` (every OTHER kind is missing). Sweep
    /// [`ConditionKind::ALL`] so a regression that returned `0` (forgot
    /// to negate), `ConditionKind::ALL.len()` (forgot the populated
    /// kind), or a per-kind constant surfaces HERE.
    #[test]
    fn condition_slice_missing_kind_count_returns_all_minus_one_per_variant() {
        for populated in ConditionKind::ALL {
            let slice = [condition_with(populated)];
            assert_eq!(
                slice.missing_kind_count(),
                ConditionKind::ALL.len() - 1,
                "single-populated slice must return ConditionKind::ALL.len() - 1 on missing_kind_count for {populated:?}",
            );
            assert_eq!(
                slice.missing_kind_count(),
                slice.missing_kinds().len(),
                "single-populated missing_kind_count must equal missing_kinds().len() for {populated:?}",
            );
        }
    }

    /// FULL-COVERAGE pin — a slice that carries every [`ConditionKind`]
    /// variant returns `0` on `missing_kind_count` (no kind is missing).
    /// Dual of the empty-slice arm above; a regression that returned
    /// `ConditionKind::ALL.len()` regardless of population or inverted
    /// the presence direction surfaces HERE.
    #[test]
    fn condition_slice_missing_kind_count_returns_zero_on_saturated_slice() {
        let saturated: Vec<Condition> =
            ConditionKind::ALL.into_iter().map(condition_with).collect();
        assert_eq!(
            saturated.as_slice().missing_kind_count(),
            0,
            "slice containing every ConditionKind must return 0 on missing_kind_count",
        );
        assert_eq!(
            saturated.as_slice().missing_kind_count(),
            saturated.as_slice().missing_kinds().len(),
            "saturated missing_kind_count must equal missing_kinds().len()",
        );
    }

    // ── ConditionSliceExt::is_kind_saturated — Boolean saturation pins ─
    //
    // Short-circuiting Boolean saturation-endpoint peer of the closed-set-
    // complement widened + scalar primitives: `is_kind_saturated()`
    // returns `true` iff every ConditionKind::ALL variant appears at
    // least once in the slice, WITHOUT allocating `missing_kinds` or
    // walking every entry to build `missing_kind_count`. The composition
    // laws `is_kind_saturated() == (missing_kind_count() == 0)` and
    // `is_kind_saturated() == missing_kinds().is_empty()` are pinned as
    // the saturation-endpoint arm of
    // `assert_slice_refinement_composition_laws`. Byte-for-byte peer of
    // `crate::tagged_union::TaggedUnion::is_saturated` one struct-layer
    // up under the SAME `<CLOSED_SET>::ALL.iter().all(has)` short-
    // circuit walk shape.

    /// EMPTY-SLICE pin — an empty slice returns `false` on
    /// `is_kind_saturated` (every kind is missing).
    #[test]
    fn condition_slice_is_kind_saturated_returns_false_on_empty_slice() {
        let empty: &[Condition] = &[];
        assert!(
            !empty.is_kind_saturated(),
            "empty slice must return false on is_kind_saturated",
        );
        assert_eq!(
            empty.is_kind_saturated(),
            empty.missing_kind_count() == 0,
            "empty is_kind_saturated must equal (missing_kind_count() == 0)",
        );
    }

    /// SINGLE-KIND pin — a slice populating exactly one variant returns
    /// `false` on any [`ConditionKind::ALL`] closed set with `N ≥ 2`
    /// (the other `N - 1` variants are missing).
    #[test]
    fn condition_slice_is_kind_saturated_returns_false_on_single_kind_slice() {
        assert!(
            ConditionKind::ALL.len() >= 2,
            "test assumes ConditionKind::ALL has ≥ 2 variants",
        );
        for populated in ConditionKind::ALL {
            let slice = [condition_with(populated)];
            assert!(
                !slice.is_kind_saturated(),
                "single-populated slice with {populated:?} must return false on is_kind_saturated",
            );
            assert_eq!(
                slice.is_kind_saturated(),
                slice.missing_kind_count() == 0,
                "single-populated is_kind_saturated must equal (missing_kind_count() == 0) for {populated:?}",
            );
        }
    }

    /// FULL-COVERAGE pin — a slice that carries every [`ConditionKind`]
    /// variant returns `true` on `is_kind_saturated` — the SOLE arm
    /// where the primitive returns `true`.
    #[test]
    fn condition_slice_is_kind_saturated_returns_true_on_saturated_slice() {
        let saturated: Vec<Condition> =
            ConditionKind::ALL.into_iter().map(condition_with).collect();
        assert!(
            saturated.as_slice().is_kind_saturated(),
            "slice containing every ConditionKind must return true on is_kind_saturated",
        );
        assert_eq!(
            saturated.as_slice().is_kind_saturated(),
            saturated.as_slice().missing_kind_count() == 0,
            "saturated is_kind_saturated must equal (missing_kind_count() == 0)",
        );
        assert_eq!(
            saturated.as_slice().is_kind_saturated(),
            saturated.as_slice().missing_kinds().is_empty(),
            "saturated is_kind_saturated must equal missing_kinds().is_empty()",
        );
    }

    /// DUPLICATE-COVERAGE pin — a slice that carries every
    /// [`ConditionKind`] variant multiple times still returns `true`
    /// (multiplicity is irrelevant to the saturation predicate on the
    /// closed-set-inversion axis).
    #[test]
    fn condition_slice_is_kind_saturated_ignores_multiplicity() {
        let mut doubled: Vec<Condition> = Vec::new();
        for k in ConditionKind::ALL {
            doubled.push(condition_with(k));
            doubled.push(condition_with(k));
        }
        assert!(
            doubled.as_slice().is_kind_saturated(),
            "slice carrying every ConditionKind twice must return true on is_kind_saturated",
        );
    }

    // ── ConditionSliceExt::has_any_distinct_kind — at-least-one halfspace pins ──
    //
    // Boolean at-least-one halfspace peer of `has_any_missing_kind` on
    // the closed-set-inversion axis: `has_any_distinct_kind()` returns
    // `true` iff AT LEAST ONE `ConditionKind::ALL` variant appears at
    // least once in the slice, via a SHORT-CIRCUITING closed-set walk
    // `ConditionKind::ALL.iter().copied().any(|k| self.has_kind(k))`
    // that returns `true` at the FIRST populated kind. The composition
    // laws `has_any_distinct_kind() == (distinct_kind_count() > 0)`,
    // `has_any_distinct_kind() == !distinct_kinds().is_empty()`, and
    // `has_any_distinct_kind() == first_distinct_kind().is_some()` are
    // pinned as the at-least-one halfspace arm of
    // `assert_slice_refinement_composition_laws` on the closed-set-
    // inversion axis. Byte-for-byte peer of
    // `crate::tagged_union::TaggedUnion::has_any_populated_kind` one
    // struct-layer up under the SAME `any(has)` short-circuit shape.

    /// EMPTY-SLICE pin — an empty slice returns `false` on
    /// `has_any_distinct_kind` (no kind is present) — the SOLE arm
    /// where the primitive returns `false`. Dual of the empty-slice
    /// arm on `has_any_missing_kind` (which returns `true`).
    #[test]
    fn condition_slice_has_any_distinct_kind_returns_false_on_empty_slice() {
        let empty: &[Condition] = &[];
        assert!(
            !empty.has_any_distinct_kind(),
            "empty slice must return false on has_any_distinct_kind",
        );
        assert_eq!(
            empty.has_any_distinct_kind(),
            empty.distinct_kind_count() > 0,
            "empty has_any_distinct_kind must equal (distinct_kind_count() > 0)",
        );
        assert_eq!(
            empty.has_any_distinct_kind(),
            !empty.distinct_kinds().is_empty(),
            "empty has_any_distinct_kind must equal !distinct_kinds().is_empty()",
        );
        assert_eq!(
            empty.has_any_distinct_kind(),
            empty.first_distinct_kind().is_some(),
            "empty has_any_distinct_kind must equal first_distinct_kind().is_some()",
        );
    }

    /// SINGLE-KIND pin — a slice populating exactly one variant
    /// returns `true` on `has_any_distinct_kind` for every
    /// [`ConditionKind`] (a single element contributes one distinct
    /// kind, ≥ 1). Also pins the composition law
    /// `has_any_distinct_kind() == (distinct_kind_count() > 0)` at
    /// the single-populated arm.
    #[test]
    fn condition_slice_has_any_distinct_kind_returns_true_on_single_kind_slice() {
        for populated in ConditionKind::ALL {
            let slice = [condition_with(populated)];
            assert!(
                slice.has_any_distinct_kind(),
                "single-populated slice with {populated:?} must return true on has_any_distinct_kind",
            );
            assert_eq!(
                slice.has_any_distinct_kind(),
                slice.distinct_kind_count() > 0,
                "single-populated has_any_distinct_kind must equal (distinct_kind_count() > 0) for {populated:?}",
            );
        }
    }

    /// FULL-COVERAGE pin — a slice that carries every
    /// [`ConditionKind`] variant returns `true` on
    /// `has_any_distinct_kind`. Dual of the FULL-COVERAGE arm on
    /// `has_any_missing_kind` (which returns `false`) — the two
    /// Booleans DISAGREE on the saturated arm.
    #[test]
    fn condition_slice_has_any_distinct_kind_returns_true_on_saturated_slice() {
        let saturated: Vec<Condition> =
            ConditionKind::ALL.into_iter().map(condition_with).collect();
        assert!(
            saturated.as_slice().has_any_distinct_kind(),
            "slice containing every ConditionKind must return true on has_any_distinct_kind",
        );
        assert_eq!(
            saturated.as_slice().has_any_distinct_kind(),
            !saturated.as_slice().distinct_kinds().is_empty(),
            "saturated has_any_distinct_kind must equal !distinct_kinds().is_empty()",
        );
    }

    /// DUPLICATE-COVERAGE pin — a slice that carries the SAME
    /// [`ConditionKind`] multiple times still returns `true`
    /// (multiplicity is irrelevant to the at-least-one halfspace
    /// predicate on the closed-set-inversion axis, byte-for-byte peer
    /// of the closed-set-complement halfspace arm).
    #[test]
    fn condition_slice_has_any_distinct_kind_ignores_multiplicity() {
        for k in ConditionKind::ALL {
            let doubled: Vec<Condition> = vec![condition_with(k), condition_with(k)];
            assert!(
                doubled.as_slice().has_any_distinct_kind(),
                "slice carrying {k:?} twice must return true on has_any_distinct_kind",
            );
        }
    }

    // ── ConditionSliceExt::has_unique_distinct_kind — cardinality-mid-endpoint pins ──
    //
    // Boolean cardinality-mid-endpoint peer of `has_any_distinct_kind`
    // on the closed-set-inversion axis: returns `true` iff EXACTLY
    // ONE `ConditionKind::ALL` variant appears at least once in the
    // slice. Body folds through the load-bearing
    // `iter_distinct_kinds` iterator under a two-step short-circuit;
    // strictly cheaper than `distinct_kind_count() == 1` (which walks
    // every slot) and `distinct_kinds().len() == 1` (which allocates
    // the Vec) on every arm with ≥ 2 distinct kinds. The composition
    // laws `has_unique_distinct_kind() == (distinct_kind_count() == 1)`
    // and `has_unique_distinct_kind() == (distinct_kinds().len() == 1)`
    // are pinned as the cardinality-mid-endpoint arm of
    // `assert_slice_refinement_composition_laws`. Byte-for-byte peer
    // of `crate::tagged_union::TaggedUnion::has_unique_populated_kind`
    // one struct-layer up under the SAME two-step short-circuit walk
    // shape.

    /// EMPTY-SLICE pin — an empty slice returns `false` on
    /// `has_unique_distinct_kind` (zero distinct, not exactly 1).
    /// Also pins the composition law `has_unique_distinct_kind() ==
    /// (distinct_kind_count() == 1)` at zero-distinct.
    #[test]
    fn condition_slice_has_unique_distinct_kind_returns_false_on_empty_slice() {
        let empty: &[Condition] = &[];
        assert!(
            !empty.has_unique_distinct_kind(),
            "empty slice must return false on has_unique_distinct_kind (0 distinct, not exactly 1)",
        );
        assert_eq!(
            empty.has_unique_distinct_kind(),
            empty.distinct_kind_count() == 1,
            "empty has_unique_distinct_kind must equal (distinct_kind_count() == 1)",
        );
    }

    /// SINGLE-KIND pin — a slice populating exactly one variant
    /// returns `true` on `has_unique_distinct_kind` for every
    /// [`ConditionKind`] — the SOLE arrangement where the primitive
    /// returns `true` on any `N ≥ 2` closed set (the singleton-
    /// coverage arm). Also pins the widened composition law
    /// `has_unique_distinct_kind() == (distinct_kinds().len() == 1)`.
    #[test]
    fn condition_slice_has_unique_distinct_kind_returns_true_on_single_kind_slice() {
        for populated in ConditionKind::ALL {
            let slice = [condition_with(populated)];
            assert!(
                slice.has_unique_distinct_kind(),
                "single-populated slice with {populated:?} must return true on has_unique_distinct_kind",
            );
            assert_eq!(
                slice.has_unique_distinct_kind(),
                slice.distinct_kind_count() == 1,
                "single-populated has_unique_distinct_kind must equal (distinct_kind_count() == 1) for {populated:?}",
            );
            assert_eq!(
                slice.has_unique_distinct_kind(),
                slice.distinct_kinds().len() == 1,
                "single-populated has_unique_distinct_kind must equal (distinct_kinds().len() == 1) for {populated:?}",
            );
            assert_eq!(
                slice.first_distinct_kind(),
                Some(populated),
                "single-populated first_distinct_kind must name the SOLE covered kind for {populated:?}",
            );
        }
    }

    /// SATURATED pin — a slice carrying every [`ConditionKind`]
    /// returns `false` on `has_unique_distinct_kind` on any `N ≥ 2`
    /// closed set (`N` distinct, not exactly 1). Dual of the
    /// SATURATED arm on `has_any_distinct_kind` which returns `true`
    /// — the two Booleans DISAGREE on the saturated arm.
    #[test]
    fn condition_slice_has_unique_distinct_kind_returns_false_on_saturated_slice() {
        assert!(
            ConditionKind::ALL.len() >= 2,
            "test assumes ConditionKind::ALL has ≥ 2 variants",
        );
        let saturated: Vec<Condition> =
            ConditionKind::ALL.into_iter().map(condition_with).collect();
        assert!(
            !saturated.as_slice().has_unique_distinct_kind(),
            "saturated slice must return false on has_unique_distinct_kind ({} distinct, not exactly 1)",
            ConditionKind::ALL.len(),
        );
        assert_eq!(
            saturated.as_slice().has_unique_distinct_kind(),
            saturated.as_slice().distinct_kind_count() == 1,
            "saturated has_unique_distinct_kind must equal (distinct_kind_count() == 1)",
        );
    }

    /// TWO-POPULATED pin — a slice carrying exactly two distinct
    /// [`ConditionKind`] variants returns `false` on
    /// `has_unique_distinct_kind` (2 distinct, not exactly 1). Pins
    /// the SECOND-slot short-circuit boundary — a regression that
    /// dropped the second-slot check (returning `true` on any
    /// at-least-one arm) surfaces HERE. Only meaningful on `N ≥ 2`
    /// closed sets.
    #[test]
    fn condition_slice_has_unique_distinct_kind_returns_false_on_two_populated_slice() {
        assert!(
            ConditionKind::ALL.len() >= 2,
            "test assumes ConditionKind::ALL has ≥ 2 variants",
        );
        for i in 0..ConditionKind::ALL.len() {
            for j in (i + 1)..ConditionKind::ALL.len() {
                let two_populated: Vec<Condition> = vec![
                    condition_with(ConditionKind::ALL[i]),
                    condition_with(ConditionKind::ALL[j]),
                ];
                let slice = two_populated.as_slice();
                assert!(
                    !slice.has_unique_distinct_kind(),
                    "two-populated slice (kinds at index {i} and {j}) must return false on has_unique_distinct_kind (2 distinct, not exactly 1)",
                );
                assert_eq!(
                    slice.has_unique_distinct_kind(),
                    slice.distinct_kind_count() == 1,
                    "two-populated has_unique_distinct_kind must equal (distinct_kind_count() == 1) for kinds=({i}, {j})",
                );
            }
        }
    }

    /// MULTIPLICITY pin — a slice carrying the SAME [`ConditionKind`]
    /// multiple times still returns `true` (multiplicity is
    /// irrelevant to the cardinality-mid-endpoint projection on the
    /// closed-set-inversion axis — one distinct kind regardless of
    /// repetition count, byte-for-byte peer of the at-least-one
    /// halfspace arm's multiplicity pin).
    #[test]
    fn condition_slice_has_unique_distinct_kind_ignores_multiplicity() {
        for k in ConditionKind::ALL {
            let doubled: Vec<Condition> = vec![condition_with(k), condition_with(k)];
            assert!(
                doubled.as_slice().has_unique_distinct_kind(),
                "slice carrying {k:?} twice must return true on has_unique_distinct_kind (still 1 distinct)",
            );
            let tripled: Vec<Condition> =
                vec![condition_with(k), condition_with(k), condition_with(k)];
            assert!(
                tripled.as_slice().has_unique_distinct_kind(),
                "slice carrying {k:?} three times must return true on has_unique_distinct_kind (still 1 distinct)",
            );
        }
    }

    // ── ConditionSliceExt::has_multiple_distinct_kinds — cardinality-many-arm pins ──
    //
    // Boolean cardinality many-arm peer of `has_unique_distinct_kind`
    // on the closed-set-inversion axis: `has_multiple_distinct_kinds()`
    // returns `true` iff AT LEAST TWO `ConditionKind::ALL` variants
    // appear at least once in the slice, byte-for-byte with a two-step-
    // short-circuit walk over `iter_distinct_kinds`. The composition
    // laws `has_multiple_distinct_kinds() == (distinct_kind_count() >= 2)`
    // and `has_multiple_distinct_kinds() == (distinct_kinds().len() >= 2)`
    // are pinned as the cardinality-many-arm arm of
    // `assert_slice_refinement_composition_laws`. Byte-for-byte peer of
    // `crate::tagged_union::TaggedUnion::has_multiple_populated_kinds`
    // one struct-layer up under the SAME two-step short-circuit walk
    // shape.

    /// EMPTY-SLICE pin — an empty slice returns `false` on
    /// `has_multiple_distinct_kinds` (0 distinct, not ≥ 2). Dual of
    /// the empty-slice arm on `has_multiple_missing_kinds` which
    /// returns `true`. Also pins the composition law
    /// `has_multiple_distinct_kinds() == (distinct_kind_count() >= 2)`
    /// at zero-distinct.
    #[test]
    fn condition_slice_has_multiple_distinct_kinds_returns_false_on_empty_slice() {
        let empty: &[Condition] = &[];
        assert!(
            !empty.has_multiple_distinct_kinds(),
            "empty slice must return false on has_multiple_distinct_kinds (0 distinct, not ≥ 2)",
        );
        assert_eq!(
            empty.has_multiple_distinct_kinds(),
            empty.distinct_kind_count() >= 2,
            "empty has_multiple_distinct_kinds must equal (distinct_kind_count() >= 2)",
        );
    }

    /// SINGLE-KIND pin — a slice populating exactly one variant
    /// returns `false` on `has_multiple_distinct_kinds` (1 distinct,
    /// not ≥ 2). The SOLE-populated arrangement where the many-arm
    /// primitive returns `false` alongside the empty-endpoint — the
    /// definitional boundary between the =1 mid-endpoint and the ≥ 2
    /// many-arm on the distinct axis. Also pins the widened
    /// composition law
    /// `has_multiple_distinct_kinds() == (distinct_kinds().len() >= 2)`.
    #[test]
    fn condition_slice_has_multiple_distinct_kinds_returns_false_on_single_kind_slice() {
        for populated in ConditionKind::ALL {
            let slice = [condition_with(populated)];
            assert!(
                !slice.has_multiple_distinct_kinds(),
                "single-populated slice with {populated:?} must return false on has_multiple_distinct_kinds (1 distinct, not ≥ 2)",
            );
            assert_eq!(
                slice.has_multiple_distinct_kinds(),
                slice.distinct_kind_count() >= 2,
                "single-populated has_multiple_distinct_kinds must equal (distinct_kind_count() >= 2) for {populated:?}",
            );
            assert_eq!(
                slice.has_multiple_distinct_kinds(),
                slice.distinct_kinds().len() >= 2,
                "single-populated has_multiple_distinct_kinds must equal (distinct_kinds().len() >= 2) for {populated:?}",
            );
        }
    }

    /// SATURATED pin — a slice carrying every [`ConditionKind`]
    /// variant returns `true` on `has_multiple_distinct_kinds` on any
    /// `N ≥ 2` closed set (`N` distinct, ≥ 2). Dual of the SATURATED
    /// arm on `has_unique_distinct_kind` which returns `false` on
    /// `N ≥ 2`.
    #[test]
    fn condition_slice_has_multiple_distinct_kinds_returns_true_on_saturated_slice() {
        assert!(
            ConditionKind::ALL.len() >= 2,
            "test assumes ConditionKind::ALL has ≥ 2 variants",
        );
        let saturated: Vec<Condition> =
            ConditionKind::ALL.into_iter().map(condition_with).collect();
        assert!(
            saturated.as_slice().has_multiple_distinct_kinds(),
            "saturated slice must return true on has_multiple_distinct_kinds ({} distinct, ≥ 2)",
            ConditionKind::ALL.len(),
        );
        assert_eq!(
            saturated.as_slice().has_multiple_distinct_kinds(),
            saturated.as_slice().distinct_kind_count() >= 2,
            "saturated has_multiple_distinct_kinds must equal (distinct_kind_count() >= 2)",
        );
    }

    /// TWO-POPULATED pin — a slice carrying exactly two distinct
    /// [`ConditionKind`] variants returns `true` on
    /// `has_multiple_distinct_kinds` (2 distinct, ≥ 2). Pins the
    /// SECOND-slot boundary of the ≥ 2 arm — a regression that
    /// dropped the second-slot short-circuit (conflating with the
    /// at-least-one halfspace, returning `true` on any partial
    /// arrangement) would still pass here; complemented by the
    /// SINGLE-KIND pin which distinguishes the =1 arm from the ≥ 2
    /// arm. Only meaningful on `N ≥ 2` closed sets.
    #[test]
    fn condition_slice_has_multiple_distinct_kinds_returns_true_on_two_populated_slice() {
        assert!(
            ConditionKind::ALL.len() >= 2,
            "test assumes ConditionKind::ALL has ≥ 2 variants",
        );
        for i in 0..ConditionKind::ALL.len() {
            for j in (i + 1)..ConditionKind::ALL.len() {
                let two_populated: Vec<Condition> = vec![
                    condition_with(ConditionKind::ALL[i]),
                    condition_with(ConditionKind::ALL[j]),
                ];
                let slice = two_populated.as_slice();
                assert!(
                    slice.has_multiple_distinct_kinds(),
                    "two-populated slice (kinds at index {i} and {j}) must return true on has_multiple_distinct_kinds (2 distinct, ≥ 2)",
                );
                assert_eq!(
                    slice.has_multiple_distinct_kinds(),
                    slice.distinct_kind_count() >= 2,
                    "two-populated has_multiple_distinct_kinds must equal (distinct_kind_count() >= 2) for kinds=({i}, {j})",
                );
            }
        }
    }

    /// MULTIPLICITY pin — a slice carrying the SAME [`ConditionKind`]
    /// multiple times still returns `false` on
    /// `has_multiple_distinct_kinds` (multiplicity is irrelevant to
    /// the cardinality-many-arm projection on the closed-set-inversion
    /// axis — one distinct kind regardless of repetition count).
    #[test]
    fn condition_slice_has_multiple_distinct_kinds_ignores_multiplicity() {
        for k in ConditionKind::ALL {
            let doubled: Vec<Condition> = vec![condition_with(k), condition_with(k)];
            assert!(
                !doubled.as_slice().has_multiple_distinct_kinds(),
                "slice carrying {k:?} twice must return false on has_multiple_distinct_kinds (still 1 distinct)",
            );
            let tripled: Vec<Condition> =
                vec![condition_with(k), condition_with(k), condition_with(k)];
            assert!(
                !tripled.as_slice().has_multiple_distinct_kinds(),
                "slice carrying {k:?} three times must return false on has_multiple_distinct_kinds (still 1 distinct)",
            );
        }
    }

    // ── ConditionSliceExt::has_multiple_of_kind — per-kind "≥ 2" pins ─
    //
    // Boolean cardinality "≥ 2" many-arm peer of `has_kind` (≥ 1) and
    // `lacks_kind` (= 0) on the per-kind count axis:
    // `has_multiple_of_kind(k)` returns `true` iff AT LEAST TWO
    // `Condition` values with kind `k` appear in the slice. Composes
    // through a two-step short-circuit walk over `iter_kind(k)` —
    // byte-for-byte peer of `has_multiple_distinct_kinds` one axis
    // over (whole-slice distinct kinds vs per-kind matches). The
    // composition laws `has_multiple_of_kind(k) == (count_kind(k) >= 2)`,
    // `has_multiple_of_kind(k) == (iter_kind(k).count() >= 2)`, and
    // `has_multiple_of_kind(k) == { iter_kind(k) two-step short-circuit }`
    // are pinned as the per-kind many-arm of
    // `assert_slice_refinement_composition_laws`. Detects duplicate
    // conditions of a specific kind — the substrate primitive that a
    // future boundary-well-formedness coherence check (reject a
    // Process whose preconditions carry duplicate `ProcessPhase`
    // entries) or `has-multiple-of-<kind>` require-tag classifier
    // arm reaches through with no allocation.

    /// EMPTY-SLICE pin — an empty slice returns `false` on
    /// `has_multiple_of_kind` for EVERY kind (0 matches, not ≥ 2).
    /// Also pins the composition law
    /// `has_multiple_of_kind(k) == (count_kind(k) >= 2)` at zero-count
    /// for every kind.
    #[test]
    fn condition_slice_has_multiple_of_kind_returns_false_on_empty_slice() {
        let empty: &[Condition] = &[];
        for k in ConditionKind::ALL {
            assert!(
                !empty.has_multiple_of_kind(k),
                "empty slice must return false on has_multiple_of_kind({k:?}) (0 matches, not ≥ 2)",
            );
            assert_eq!(
                empty.has_multiple_of_kind(k),
                empty.count_kind(k) >= 2,
                "empty has_multiple_of_kind({k:?}) must equal (count_kind({k:?}) >= 2)",
            );
        }
    }

    /// COUNT-AXIS pin — sweeps a range of per-kind multiplicities
    /// (0, 1, 2, 3) and asserts the primitive equals
    /// `count_kind(k) >= 2` at each arm. Pins the transition from
    /// the =1 (single-match) arm where the primitive returns
    /// `false` to the =2 (duplicate) arm where it returns `true`.
    /// Also pins per-kind independence: multiplicity of OTHER kinds
    /// is irrelevant.
    #[test]
    fn condition_slice_has_multiple_of_kind_tracks_count_kind_ge_two() {
        for target in ConditionKind::ALL {
            for target_multiplicity in [0usize, 1, 2, 3] {
                // Build a slice with `target` repeated
                // `target_multiplicity` times, plus one instance of
                // every OTHER kind. `has_multiple_of_kind(target)`
                // must depend only on `target_multiplicity`.
                let mut slice: Vec<Condition> = Vec::new();
                for _ in 0..target_multiplicity {
                    slice.push(condition_with(target));
                }
                for other in ConditionKind::ALL {
                    if other != target {
                        slice.push(condition_with(other));
                    }
                }
                let s = slice.as_slice();

                assert_eq!(
                    s.has_multiple_of_kind(target),
                    target_multiplicity >= 2,
                    "has_multiple_of_kind({target:?}) with multiplicity {target_multiplicity} \
                     must equal ({target_multiplicity} >= 2)",
                );
                assert_eq!(
                    s.has_multiple_of_kind(target),
                    s.count_kind(target) >= 2,
                    "has_multiple_of_kind({target:?}) drifted from (count_kind >= 2) at \
                     multiplicity {target_multiplicity}",
                );
                assert_eq!(
                    s.has_multiple_of_kind(target),
                    s.iter_kind(target).count() >= 2,
                    "has_multiple_of_kind({target:?}) drifted from (iter_kind.count() >= 2) \
                     at multiplicity {target_multiplicity}",
                );

                // OTHER kinds appear exactly once; their many-arm
                // stays `false` regardless of `target`'s multiplicity.
                for other in ConditionKind::ALL {
                    if other != target {
                        assert!(
                            !s.has_multiple_of_kind(other),
                            "other kind {other:?} present once must return false on \
                             has_multiple_of_kind (target={target:?} mult={target_multiplicity})",
                        );
                    }
                }
            }
        }
    }

    // ── ConditionSliceExt::has_unique_of_kind — per-kind "= 1" pins ─
    //
    // Boolean cardinality "= 1" mid-endpoint peer of `lacks_kind`
    // (= 0) and `has_multiple_of_kind` (≥ 2) on the per-kind count
    // axis: `has_unique_of_kind(k)` returns `true` iff EXACTLY ONE
    // `Condition` value with kind `k` appears in the slice. Composes
    // through a two-step short-circuit walk over `iter_kind(k)` —
    // byte-for-byte peer of `has_multiple_of_kind` under the
    // (= 1, ≥ 2) count-axis duality (both walk the same iterator,
    // differing only in the second-hit predicate: `is_none` here vs
    // `is_some` on the many-arm peer). Closes the {= 0, = 1, ≥ 2}
    // per-kind cardinality Boolean trichotomy at the slice level:
    // EXACTLY ONE of {lacks_kind, has_unique_of_kind,
    // has_multiple_of_kind} fires on any `(slice, kind)` pair, pinned
    // as the per-kind trichotomy partition arm of
    // `assert_slice_refinement_composition_laws` alongside the per-
    // kind mid-endpoint composition-law arms
    // `has_unique_of_kind(k) == (count_kind(k) == 1)`,
    // `has_unique_of_kind(k) == (iter_kind(k).count() == 1)`, and
    // `has_unique_of_kind(k) == { iter_kind(k) two-step short-circuit }`.
    // Detects singleton conditions of a specific kind — the substrate
    // primitive that a future boundary-well-formedness coherence
    // check (enforce a Process's preconditions carry EXACTLY ONE
    // `ProcessPhase` entry) or `has-unique-of-<kind>` require-tag
    // classifier arm reaches through with no allocation.

    /// EMPTY-SLICE pin — an empty slice returns `false` on
    /// `has_unique_of_kind` for EVERY kind (0 matches, not = 1).
    /// Also pins the composition law
    /// `has_unique_of_kind(k) == (count_kind(k) == 1)` at zero-count
    /// for every kind.
    #[test]
    fn condition_slice_has_unique_of_kind_returns_false_on_empty_slice() {
        let empty: &[Condition] = &[];
        for k in ConditionKind::ALL {
            assert!(
                !empty.has_unique_of_kind(k),
                "empty slice must return false on has_unique_of_kind({k:?}) (0 matches, not = 1)",
            );
            assert_eq!(
                empty.has_unique_of_kind(k),
                empty.count_kind(k) == 1,
                "empty has_unique_of_kind({k:?}) must equal (count_kind({k:?}) == 1)",
            );
        }
    }

    /// COUNT-AXIS pin — sweeps a range of per-kind multiplicities
    /// (0, 1, 2, 3) and asserts the primitive equals
    /// `count_kind(k) == 1` at each arm. Pins the transition from
    /// the =0 (empty) arm where the primitive returns `false`
    /// through the =1 (singleton) arm where it returns `true` back
    /// to the =2 (duplicate) arm where it returns `false`. Also
    /// pins per-kind independence: multiplicity of OTHER kinds
    /// (each present exactly once) leaves the mid-endpoint of every
    /// other kind at `true` regardless of `target`'s multiplicity.
    #[test]
    fn condition_slice_has_unique_of_kind_tracks_count_kind_eq_one() {
        for target in ConditionKind::ALL {
            for target_multiplicity in [0usize, 1, 2, 3] {
                // Build a slice with `target` repeated
                // `target_multiplicity` times, plus one instance of
                // every OTHER kind. `has_unique_of_kind(target)`
                // must depend only on `target_multiplicity`.
                let mut slice: Vec<Condition> = Vec::new();
                for _ in 0..target_multiplicity {
                    slice.push(condition_with(target));
                }
                for other in ConditionKind::ALL {
                    if other != target {
                        slice.push(condition_with(other));
                    }
                }
                let s = slice.as_slice();

                assert_eq!(
                    s.has_unique_of_kind(target),
                    target_multiplicity == 1,
                    "has_unique_of_kind({target:?}) with multiplicity {target_multiplicity} \
                     must equal ({target_multiplicity} == 1)",
                );
                assert_eq!(
                    s.has_unique_of_kind(target),
                    s.count_kind(target) == 1,
                    "has_unique_of_kind({target:?}) drifted from (count_kind == 1) at \
                     multiplicity {target_multiplicity}",
                );
                assert_eq!(
                    s.has_unique_of_kind(target),
                    s.iter_kind(target).count() == 1,
                    "has_unique_of_kind({target:?}) drifted from (iter_kind.count() == 1) \
                     at multiplicity {target_multiplicity}",
                );

                // OTHER kinds appear exactly once; their mid-endpoint
                // stays `true` regardless of `target`'s multiplicity.
                for other in ConditionKind::ALL {
                    if other != target {
                        assert!(
                            s.has_unique_of_kind(other),
                            "other kind {other:?} present once must return true on \
                             has_unique_of_kind (target={target:?} mult={target_multiplicity})",
                        );
                    }
                }

                // Per-kind cardinality Boolean trichotomy pin —
                // EXACTLY ONE of {lacks_kind, has_unique_of_kind,
                // has_multiple_of_kind} fires on `(s, target)`. The
                // slice-level closure of the {=0, =1, ≥2} arms.
                let arms_true = [
                    s.lacks_kind(target),
                    s.has_unique_of_kind(target),
                    s.has_multiple_of_kind(target),
                ]
                .into_iter()
                .filter(|&b| b)
                .count();
                assert_eq!(
                    arms_true, 1,
                    "per-kind trichotomy for target={target:?} at mult={target_multiplicity} \
                     must have EXACTLY one arm true, got {arms_true}",
                );
            }
        }
    }

    // ── ConditionSliceExt::has_at_most_one_of_kind — per-kind "≤ 1" pins ─
    //
    // Boolean cardinality "≤ 1" negation peer of `has_multiple_of_kind`
    // (≥ 2) on the per-kind count axis: `has_at_most_one_of_kind(k)`
    // returns `true` iff AT MOST ONE `Condition` value with kind `k`
    // appears in the slice, byte-for-byte with
    // `!has_multiple_of_kind(k)` via the definitional negation in the
    // trait's default body. Closes the {= 0, = 1, ≥ 1, ≥ 2, ≤ 1}
    // Boolean-cardinality grid on the per-kind axis. The composition
    // laws
    // `has_at_most_one_of_kind(k) == !has_multiple_of_kind(k)`,
    // `has_at_most_one_of_kind(k) == (count_kind(k) <= 1)`,
    // `has_at_most_one_of_kind(k) == (iter_kind(k).count() <= 1)`, and
    // `has_at_most_one_of_kind(k) == lacks_kind(k) || has_unique_of_kind(k)`
    // bind the per-kind "≤ 1" projection to the widened + scalar +
    // trichotomy-union primitives. Axis-parity peer of the distinct-
    // and missing-axis "≤ 1" negations
    // (`has_at_most_one_distinct_kind ↔ !has_multiple_distinct_kinds`,
    // `has_at_most_one_missing_kind ↔ !has_multiple_missing_kinds`)
    // at the same slice-level trait under the SAME definitional
    // negation shape.

    /// EMPTY-SLICE pin — an empty slice returns `true` on
    /// `has_at_most_one_of_kind` for EVERY kind (0 matches, `≤ 1`).
    /// Also pins the composition law
    /// `has_at_most_one_of_kind(k) == !has_multiple_of_kind(k)` at
    /// zero-count for every kind and the trichotomy-union law
    /// `has_at_most_one_of_kind(k) == lacks_kind(k) ||
    /// has_unique_of_kind(k)` (=0 arm, `lacks_kind` fires).
    #[test]
    fn condition_slice_has_at_most_one_of_kind_returns_true_on_empty_slice() {
        let empty: &[Condition] = &[];
        for k in ConditionKind::ALL {
            assert!(
                empty.has_at_most_one_of_kind(k),
                "empty slice must return true on has_at_most_one_of_kind({k:?}) (0 matches, ≤ 1)",
            );
            assert_eq!(
                empty.has_at_most_one_of_kind(k),
                !empty.has_multiple_of_kind(k),
                "empty has_at_most_one_of_kind({k:?}) must equal !has_multiple_of_kind({k:?})",
            );
            assert_eq!(
                empty.has_at_most_one_of_kind(k),
                empty.count_kind(k) <= 1,
                "empty has_at_most_one_of_kind({k:?}) must equal (count_kind({k:?}) <= 1)",
            );
            assert_eq!(
                empty.has_at_most_one_of_kind(k),
                empty.lacks_kind(k) || empty.has_unique_of_kind(k),
                "empty has_at_most_one_of_kind({k:?}) must equal \
                 (lacks_kind({k:?}) || has_unique_of_kind({k:?}))",
            );
        }
    }

    /// COUNT-AXIS pin — sweeps a range of per-kind multiplicities
    /// (0, 1, 2, 3) and asserts the primitive equals
    /// `count_kind(k) <= 1` at each arm. Pins the transition from
    /// the =1 (singleton) arm where the primitive returns `true` to
    /// the =2 (duplicate) arm where it returns `false`, byte-for-byte
    /// with the definitional negation of `has_multiple_of_kind` at
    /// each multiplicity. Also pins per-kind independence: multiplicity
    /// of OTHER kinds (each present exactly once) leaves the "≤ 1"
    /// arm of every other kind at `true` regardless of `target`'s
    /// multiplicity.
    #[test]
    fn condition_slice_has_at_most_one_of_kind_tracks_count_kind_le_one() {
        for target in ConditionKind::ALL {
            for target_multiplicity in [0usize, 1, 2, 3] {
                // Build a slice with `target` repeated
                // `target_multiplicity` times, plus one instance of
                // every OTHER kind. `has_at_most_one_of_kind(target)`
                // must depend only on `target_multiplicity`.
                let mut slice: Vec<Condition> = Vec::new();
                for _ in 0..target_multiplicity {
                    slice.push(condition_with(target));
                }
                for other in ConditionKind::ALL {
                    if other != target {
                        slice.push(condition_with(other));
                    }
                }
                let s = slice.as_slice();

                assert_eq!(
                    s.has_at_most_one_of_kind(target),
                    target_multiplicity <= 1,
                    "has_at_most_one_of_kind({target:?}) with multiplicity {target_multiplicity} \
                     must equal ({target_multiplicity} <= 1)",
                );
                assert_eq!(
                    s.has_at_most_one_of_kind(target),
                    !s.has_multiple_of_kind(target),
                    "has_at_most_one_of_kind({target:?}) drifted from !has_multiple_of_kind at \
                     multiplicity {target_multiplicity}",
                );
                assert_eq!(
                    s.has_at_most_one_of_kind(target),
                    s.count_kind(target) <= 1,
                    "has_at_most_one_of_kind({target:?}) drifted from (count_kind <= 1) at \
                     multiplicity {target_multiplicity}",
                );
                assert_eq!(
                    s.has_at_most_one_of_kind(target),
                    s.iter_kind(target).count() <= 1,
                    "has_at_most_one_of_kind({target:?}) drifted from (iter_kind.count() <= 1) \
                     at multiplicity {target_multiplicity}",
                );
                // Trichotomy-union arm: {= 0} ∪ {= 1} == {≤ 1}.
                assert_eq!(
                    s.has_at_most_one_of_kind(target),
                    s.lacks_kind(target) || s.has_unique_of_kind(target),
                    "has_at_most_one_of_kind({target:?}) drifted from \
                     (lacks_kind || has_unique_of_kind) at multiplicity {target_multiplicity}",
                );

                // OTHER kinds appear exactly once; their "≤ 1" arm
                // stays `true` regardless of `target`'s multiplicity.
                for other in ConditionKind::ALL {
                    if other != target {
                        assert!(
                            s.has_at_most_one_of_kind(other),
                            "other kind {other:?} present once must return true on \
                             has_at_most_one_of_kind (target={target:?} mult={target_multiplicity})",
                        );
                    }
                }

                // Boolean tetrachotomy pin — for a given per-kind
                // multiplicity, {has_at_most_one_of_kind,
                // has_multiple_of_kind} PARTITION the count axis
                // under the definitional negation (EXACTLY ONE fires
                // on any `(s, target)` pair). Also verifies the
                // relationship with the {= 0, = 1, ≥ 2} trichotomy:
                // `has_at_most_one_of_kind` fires iff either
                // `lacks_kind` or `has_unique_of_kind` fires.
                let at_most_one = s.has_at_most_one_of_kind(target);
                let multiple = s.has_multiple_of_kind(target);
                assert_ne!(
                    at_most_one, multiple,
                    "per-kind {{≤1, ≥2}} Boolean-negation partition for target={target:?} at \
                     mult={target_multiplicity} must fire EXACTLY one arm",
                );
            }
        }
    }

    // ── ConditionSliceExt::has_at_most_one_distinct_kind — "≤ 1" pins ─
    //
    // Boolean cardinality "≤ 1" negation peer of
    // `has_multiple_distinct_kinds` on the closed-set-inversion axis:
    // `has_at_most_one_distinct_kind()` returns `true` iff AT MOST ONE
    // `ConditionKind::ALL` variant appears at least once in the slice,
    // byte-for-byte with `!has_multiple_distinct_kinds()` via the
    // definitional negation in the trait's default body. The
    // composition laws
    // `has_at_most_one_distinct_kind() == !has_multiple_distinct_kinds()`,
    // `has_at_most_one_distinct_kind() == (distinct_kind_count() <= 1)`,
    // `has_at_most_one_distinct_kind() == (distinct_kinds().len() <= 1)`,
    // and `has_at_most_one_distinct_kind() == !has_any_distinct_kind() ||
    // has_unique_distinct_kind()` are pinned as the distinct-axis
    // "≤ 1" arm of `assert_slice_refinement_composition_laws`. Byte-
    // for-byte peer of
    // `crate::tagged_union::TaggedUnion::has_at_most_one_populated_kind`
    // one struct-layer up under the SAME `!has_multiple_populated_kinds`
    // definitional negation shape. Axis-parity mirror of the closed-
    // set-complement "≤ 1" negation peer
    // `has_at_most_one_missing_kind ↔ !has_multiple_missing_kinds` at
    // the same slice-level trait.

    /// EMPTY-SLICE pin — an empty slice returns `true` on
    /// `has_at_most_one_distinct_kind` (0 distinct, `≤ 1`). Dual of
    /// the empty-slice arm on `has_at_most_one_missing_kind` which
    /// returns `false` on `N ≥ 2` closed sets (empty means every kind
    /// missing, `N ≥ 2` missing, not `≤ 1`). Also pins the composition
    /// law `has_at_most_one_distinct_kind() == (distinct_kind_count() <= 1)`
    /// at zero-distinct.
    #[test]
    fn condition_slice_has_at_most_one_distinct_kind_returns_true_on_empty_slice() {
        let empty: &[Condition] = &[];
        assert!(
            empty.has_at_most_one_distinct_kind(),
            "empty slice must return true on has_at_most_one_distinct_kind (0 distinct, ≤ 1)",
        );
        assert_eq!(
            empty.has_at_most_one_distinct_kind(),
            empty.distinct_kind_count() <= 1,
            "empty has_at_most_one_distinct_kind must equal (distinct_kind_count() <= 1)",
        );
    }

    /// SINGLE-KIND pin — a slice populating exactly one variant
    /// returns `true` on `has_at_most_one_distinct_kind` (1 distinct,
    /// `≤ 1`). The singleton arm on the distinct-axis "≤ 1" primitive
    /// — the definitional boundary between the =1 mid-endpoint and the
    /// ≥ 2 many-arm on the distinct axis, where the "≤ 1" negation
    /// still fires. Also pins the widened composition law
    /// `has_at_most_one_distinct_kind() == (distinct_kinds().len() <= 1)`
    /// and the trichotomy-union arm
    /// `has_at_most_one_distinct_kind() == !has_any_distinct_kind() ||
    /// has_unique_distinct_kind()`.
    #[test]
    fn condition_slice_has_at_most_one_distinct_kind_returns_true_on_single_kind_slice() {
        for populated in ConditionKind::ALL {
            let slice = [condition_with(populated)];
            assert!(
                slice.has_at_most_one_distinct_kind(),
                "single-populated slice with {populated:?} must return true on has_at_most_one_distinct_kind (1 distinct, ≤ 1)",
            );
            assert_eq!(
                slice.has_at_most_one_distinct_kind(),
                !slice.has_multiple_distinct_kinds(),
                "single-populated has_at_most_one_distinct_kind must equal !has_multiple_distinct_kinds() for {populated:?}",
            );
            assert_eq!(
                slice.has_at_most_one_distinct_kind(),
                slice.distinct_kind_count() <= 1,
                "single-populated has_at_most_one_distinct_kind must equal (distinct_kind_count() <= 1) for {populated:?}",
            );
            assert_eq!(
                slice.has_at_most_one_distinct_kind(),
                slice.distinct_kinds().len() <= 1,
                "single-populated has_at_most_one_distinct_kind must equal (distinct_kinds().len() <= 1) for {populated:?}",
            );
            assert_eq!(
                slice.has_at_most_one_distinct_kind(),
                !slice.has_any_distinct_kind() || slice.has_unique_distinct_kind(),
                "single-populated has_at_most_one_distinct_kind must equal (!has_any_distinct_kind() || has_unique_distinct_kind()) for {populated:?}",
            );
        }
    }

    /// SATURATED pin — a slice carrying every [`ConditionKind`]
    /// variant returns `false` on `has_at_most_one_distinct_kind` on
    /// any `N ≥ 2` closed set (`N` distinct, not `≤ 1`). Dual of the
    /// SATURATED arm on `has_at_most_one_missing_kind` which returns
    /// `true` on `N ≥ 2` (0 missing, `≤ 1`).
    #[test]
    fn condition_slice_has_at_most_one_distinct_kind_returns_false_on_saturated_slice() {
        assert!(
            ConditionKind::ALL.len() >= 2,
            "test assumes ConditionKind::ALL has ≥ 2 variants",
        );
        let saturated: Vec<Condition> =
            ConditionKind::ALL.into_iter().map(condition_with).collect();
        assert!(
            !saturated.as_slice().has_at_most_one_distinct_kind(),
            "saturated slice must return false on has_at_most_one_distinct_kind ({} distinct, not ≤ 1)",
            ConditionKind::ALL.len(),
        );
        assert_eq!(
            saturated.as_slice().has_at_most_one_distinct_kind(),
            saturated.as_slice().distinct_kind_count() <= 1,
            "saturated has_at_most_one_distinct_kind must equal (distinct_kind_count() <= 1)",
        );
        assert_eq!(
            saturated.as_slice().has_at_most_one_distinct_kind(),
            !saturated.as_slice().has_any_distinct_kind()
                || saturated.as_slice().has_unique_distinct_kind(),
            "saturated has_at_most_one_distinct_kind must equal (!has_any_distinct_kind() || has_unique_distinct_kind())",
        );
    }

    /// TWO-POPULATED pin — a slice carrying exactly two distinct
    /// [`ConditionKind`] variants returns `false` on
    /// `has_at_most_one_distinct_kind` (2 distinct, not `≤ 1`). Pins
    /// the SECOND-slot boundary of the negation of the ≥ 2 arm — a
    /// regression that dropped the second-slot short-circuit on the
    /// many-arm primitive (returning `false` on any partial-populated
    /// arrangement, which negates to `true` here) would still pass
    /// here; complemented by the SATURATED pin which distinguishes the
    /// N-distinct arm from the 2-distinct arm. Only meaningful on
    /// `N ≥ 2` closed sets.
    #[test]
    fn condition_slice_has_at_most_one_distinct_kind_returns_false_on_two_populated_slice() {
        assert!(
            ConditionKind::ALL.len() >= 2,
            "test assumes ConditionKind::ALL has ≥ 2 variants",
        );
        for i in 0..ConditionKind::ALL.len() {
            for j in (i + 1)..ConditionKind::ALL.len() {
                let two_populated: Vec<Condition> = vec![
                    condition_with(ConditionKind::ALL[i]),
                    condition_with(ConditionKind::ALL[j]),
                ];
                let slice = two_populated.as_slice();
                assert!(
                    !slice.has_at_most_one_distinct_kind(),
                    "two-populated slice (kinds at index {i} and {j}) must return false on has_at_most_one_distinct_kind (2 distinct, not ≤ 1)",
                );
                assert_eq!(
                    slice.has_at_most_one_distinct_kind(),
                    slice.distinct_kind_count() <= 1,
                    "two-populated has_at_most_one_distinct_kind must equal (distinct_kind_count() <= 1) for kinds=({i}, {j})",
                );
            }
        }
    }

    /// MULTIPLICITY pin — a slice carrying the SAME [`ConditionKind`]
    /// multiple times still returns `true` on
    /// `has_at_most_one_distinct_kind` (multiplicity is irrelevant to
    /// the "≤ 1" projection on the closed-set-inversion axis — one
    /// distinct kind regardless of repetition count, `≤ 1`).
    #[test]
    fn condition_slice_has_at_most_one_distinct_kind_ignores_multiplicity() {
        for k in ConditionKind::ALL {
            let doubled: Vec<Condition> = vec![condition_with(k), condition_with(k)];
            assert!(
                doubled.as_slice().has_at_most_one_distinct_kind(),
                "slice carrying {k:?} twice must return true on has_at_most_one_distinct_kind (still 1 distinct, ≤ 1)",
            );
            let tripled: Vec<Condition> =
                vec![condition_with(k), condition_with(k), condition_with(k)];
            assert!(
                tripled.as_slice().has_at_most_one_distinct_kind(),
                "slice carrying {k:?} three times must return true on has_at_most_one_distinct_kind (still 1 distinct, ≤ 1)",
            );
        }
    }

    // ── ConditionSliceExt::is_kind_empty — zero-endpoint pins ──
    //
    // Boolean cardinality zero-endpoint peer of `is_kind_saturated` on
    // the closed-set-inversion axis: `is_kind_empty()` returns `true`
    // iff NO `ConditionKind::ALL` variant appears in the slice, byte-
    // for-byte with `self.iter_distinct_kinds().next().is_none()` in
    // the trait's default body. The composition laws
    // `is_kind_empty() == !has_any_distinct_kind()`,
    // `is_kind_empty() == (distinct_kind_count() == 0)`,
    // `is_kind_empty() == distinct_kinds().is_empty()`, and
    // `is_kind_empty() == iter_distinct_kinds().next().is_none()` are
    // pinned as the zero-endpoint arm on the distinct axis of
    // `assert_slice_refinement_composition_laws`. Byte-for-byte peer of
    // `crate::tagged_union::TaggedUnion::is_empty` one struct-layer up
    // under the SAME zero-endpoint short-circuit shape. Axis-parity
    // mirror of `is_kind_saturated` on the closed-set-inversion axis
    // at the same slice-level trait.

    /// EMPTY-SLICE pin — an empty slice returns `true` on
    /// `is_kind_empty` (0 distinct, = 0). The SOLE arm on any `N ≥ 1`
    /// closed set where `is_kind_empty` returns `true`, byte-for-byte
    /// peer of the SOLE arm on which `is_kind_saturated` returns `true`
    /// (a slice carrying every variant at least once) — the (empty,
    /// saturated) endpoint pair. Also pins the composition law
    /// `is_kind_empty() == (distinct_kind_count() == 0)` and
    /// `is_kind_empty() == distinct_kinds().is_empty()` at the zero
    /// endpoint.
    #[test]
    fn condition_slice_is_kind_empty_returns_true_on_empty_slice() {
        let empty: &[Condition] = &[];
        assert!(
            empty.is_kind_empty(),
            "empty slice must return true on is_kind_empty (0 distinct, = 0)",
        );
        assert_eq!(
            empty.is_kind_empty(),
            empty.distinct_kind_count() == 0,
            "empty is_kind_empty must equal (distinct_kind_count() == 0)",
        );
        assert_eq!(
            empty.is_kind_empty(),
            empty.distinct_kinds().is_empty(),
            "empty is_kind_empty must equal distinct_kinds().is_empty()",
        );
        assert_eq!(
            empty.is_kind_empty(),
            !empty.has_any_distinct_kind(),
            "empty is_kind_empty must equal !has_any_distinct_kind()",
        );
    }

    /// SINGLE-KIND pin — a slice populating exactly one variant
    /// returns `false` on `is_kind_empty` (1 distinct, not = 0). Dual
    /// of the single-kind arm on `has_any_distinct_kind` which returns
    /// `true` on any single-populated slice, and pinned complement of
    /// the single-kind arm on `has_at_most_one_distinct_kind` which
    /// returns `true` (1 distinct is `≤ 1` but not `= 0`).
    #[test]
    fn condition_slice_is_kind_empty_returns_false_on_single_kind_slice() {
        for populated in ConditionKind::ALL {
            let slice = [condition_with(populated)];
            assert!(
                !slice.is_kind_empty(),
                "single-populated slice with {populated:?} must return false on is_kind_empty (1 distinct, not = 0)",
            );
            assert_eq!(
                slice.is_kind_empty(),
                slice.distinct_kind_count() == 0,
                "single-populated is_kind_empty must equal (distinct_kind_count() == 0) for {populated:?}",
            );
            assert_eq!(
                slice.is_kind_empty(),
                !slice.has_any_distinct_kind(),
                "single-populated is_kind_empty must equal !has_any_distinct_kind() for {populated:?}",
            );
        }
    }

    /// SATURATED pin — a slice carrying every [`ConditionKind`]
    /// variant returns `false` on `is_kind_empty` on any `N ≥ 1`
    /// closed set (`N` distinct, not `= 0`). Dual of the SATURATED
    /// arm on `is_kind_saturated` which returns `true` (0 missing,
    /// `= 0` on the closed-set-complement axis) — the two Booleans
    /// name the two OPPOSITE endpoints of the (distinct, missing)
    /// partition on any non-trivial closed set.
    #[test]
    fn condition_slice_is_kind_empty_returns_false_on_saturated_slice() {
        assert!(
            !ConditionKind::ALL.is_empty(),
            "test assumes ConditionKind::ALL has ≥ 1 variants",
        );
        let saturated: Vec<Condition> =
            ConditionKind::ALL.into_iter().map(condition_with).collect();
        assert!(
            !saturated.as_slice().is_kind_empty(),
            "saturated slice must return false on is_kind_empty ({} distinct, not = 0)",
            ConditionKind::ALL.len(),
        );
        assert_eq!(
            saturated.as_slice().is_kind_empty(),
            saturated.as_slice().distinct_kind_count() == 0,
            "saturated is_kind_empty must equal (distinct_kind_count() == 0)",
        );
        assert!(
            !saturated.as_slice().is_kind_empty() && saturated.as_slice().is_kind_saturated(),
            "saturated slice must return false on is_kind_empty AND true on is_kind_saturated — the (empty, saturated) endpoint pair partitions ALL",
        );
    }

    /// TWO-POPULATED pin — a slice carrying exactly two distinct
    /// [`ConditionKind`] variants returns `false` on `is_kind_empty`
    /// (2 distinct, not `= 0`). Only meaningful on `N ≥ 2` closed
    /// sets.
    #[test]
    fn condition_slice_is_kind_empty_returns_false_on_two_populated_slice() {
        assert!(
            ConditionKind::ALL.len() >= 2,
            "test assumes ConditionKind::ALL has ≥ 2 variants",
        );
        for i in 0..ConditionKind::ALL.len() {
            for j in (i + 1)..ConditionKind::ALL.len() {
                let two_populated: Vec<Condition> = vec![
                    condition_with(ConditionKind::ALL[i]),
                    condition_with(ConditionKind::ALL[j]),
                ];
                let slice = two_populated.as_slice();
                assert!(
                    !slice.is_kind_empty(),
                    "two-populated slice (kinds at index {i} and {j}) must return false on is_kind_empty (2 distinct, not = 0)",
                );
                assert_eq!(
                    slice.is_kind_empty(),
                    slice.distinct_kind_count() == 0,
                    "two-populated is_kind_empty must equal (distinct_kind_count() == 0) for kinds=({i}, {j})",
                );
            }
        }
    }

    /// MULTIPLICITY pin — a slice carrying the SAME [`ConditionKind`]
    /// multiple times still returns `false` on `is_kind_empty` (still
    /// 1 distinct regardless of repetition count, `> 0`). Complement
    /// of the empty-slice arm — the zero-endpoint fires strictly on
    /// zero-distinct slices, never on any non-empty arrangement.
    #[test]
    fn condition_slice_is_kind_empty_returns_false_regardless_of_multiplicity() {
        for k in ConditionKind::ALL {
            let doubled: Vec<Condition> = vec![condition_with(k), condition_with(k)];
            assert!(
                !doubled.as_slice().is_kind_empty(),
                "slice carrying {k:?} twice must return false on is_kind_empty (1 distinct, not = 0)",
            );
            let tripled: Vec<Condition> =
                vec![condition_with(k), condition_with(k), condition_with(k)];
            assert!(
                !tripled.as_slice().is_kind_empty(),
                "slice carrying {k:?} three times must return false on is_kind_empty (1 distinct, not = 0)",
            );
        }
    }

    // ── ConditionSliceExt::is_kind_partially_covered — middle-arm pins ──
    //
    // Boolean cardinality parent-state middle-arm peer of
    // `is_kind_empty` (=0 zero-endpoint on the distinct axis) and
    // `is_kind_saturated` (=0 zero-endpoint on the missing axis):
    // `is_kind_partially_covered()` returns `true` iff AT LEAST ONE
    // `ConditionKind::ALL` variant is PRESENT AND AT LEAST ONE is
    // ABSENT, byte-for-byte with `!is_kind_empty() && !is_kind_saturated()`
    // via the negation-of-both-endpoints composition — but composed
    // through a FUSED short-circuit walk that can exit on the SECOND
    // `ConditionKind::ALL` slot when the two bits close. The
    // composition laws
    // `is_kind_partially_covered() == !is_kind_empty() && !is_kind_saturated()`,
    // `is_kind_partially_covered() == has_any_distinct_kind() && has_any_missing_kind()`,
    // `is_kind_partially_covered() == (distinct_kind_count() > 0 && missing_kind_count() > 0)`,
    // and the trichotomy partition law
    // `is_kind_empty + is_kind_partially_covered + is_kind_saturated == 1`
    // are pinned as the parent-state trichotomy arm of
    // `assert_slice_refinement_composition_laws`. Byte-for-byte peer of
    // `crate::tagged_union::TaggedUnion::is_partially_populated` one
    // struct-layer up under the SAME fused short-circuit walk shape.

    /// EMPTY-SLICE pin — an empty slice returns `false` on
    /// `is_kind_partially_covered` (0 distinct + N missing hits the
    /// `is_kind_empty` arm, not the middle arm). Dual of the empty-
    /// slice arm on `is_kind_empty` which returns `true` — the two
    /// primitives partition the zero-distinct endpoint.
    #[test]
    fn condition_slice_is_kind_partially_covered_returns_false_on_empty_slice() {
        let empty: &[Condition] = &[];
        assert!(
            !empty.is_kind_partially_covered(),
            "empty slice must return false on is_kind_partially_covered (0 distinct hits is_kind_empty)",
        );
        assert_eq!(
            empty.is_kind_partially_covered(),
            !empty.is_kind_empty() && !empty.is_kind_saturated(),
            "empty is_kind_partially_covered must equal (!is_kind_empty() && !is_kind_saturated())",
        );
        assert_eq!(
            empty.is_kind_partially_covered(),
            empty.has_any_distinct_kind() && empty.has_any_missing_kind(),
            "empty is_kind_partially_covered must equal (has_any_distinct_kind() && has_any_missing_kind())",
        );
    }

    /// SATURATED pin — a slice carrying every [`ConditionKind`] variant
    /// returns `false` on `is_kind_partially_covered` on any `N ≥ 1`
    /// closed set (N distinct + 0 missing hits the `is_kind_saturated`
    /// arm, not the middle arm). Dual of the SATURATED arm on
    /// `is_kind_saturated` which returns `true`.
    #[test]
    fn condition_slice_is_kind_partially_covered_returns_false_on_saturated_slice() {
        assert!(
            !ConditionKind::ALL.is_empty(),
            "test assumes ConditionKind::ALL has ≥ 1 variants",
        );
        let saturated: Vec<Condition> =
            ConditionKind::ALL.into_iter().map(condition_with).collect();
        assert!(
            !saturated.as_slice().is_kind_partially_covered(),
            "saturated slice must return false on is_kind_partially_covered (0 missing hits is_kind_saturated)",
        );
        assert_eq!(
            saturated.as_slice().is_kind_partially_covered(),
            !saturated.as_slice().is_kind_empty() && !saturated.as_slice().is_kind_saturated(),
            "saturated is_kind_partially_covered must equal (!is_kind_empty() && !is_kind_saturated())",
        );
    }

    /// SINGLE-KIND pin — a slice populating exactly one variant on any
    /// `N ≥ 2` closed set returns `true` on `is_kind_partially_covered`
    /// (1 distinct + N-1 missing sits in the (open, open) product).
    /// The SOLE arm where the middle predicate FIRST fires on a well-
    /// formed slice one step away from empty.
    #[test]
    fn condition_slice_is_kind_partially_covered_returns_true_on_single_kind_slice() {
        assert!(
            ConditionKind::ALL.len() >= 2,
            "test assumes ConditionKind::ALL has ≥ 2 variants",
        );
        for populated in ConditionKind::ALL {
            let slice = [condition_with(populated)];
            assert!(
                slice.is_kind_partially_covered(),
                "single-populated slice with {populated:?} must return true on is_kind_partially_covered (1 distinct + N-1 missing)",
            );
            assert_eq!(
                slice.is_kind_partially_covered(),
                slice.has_any_distinct_kind() && slice.has_any_missing_kind(),
                "single-populated is_kind_partially_covered must equal (has_any_distinct_kind() && has_any_missing_kind()) for {populated:?}",
            );
            assert_eq!(
                slice.is_kind_partially_covered(),
                slice.distinct_kind_count() > 0 && slice.missing_kind_count() > 0,
                "single-populated is_kind_partially_covered must equal (distinct_kind_count() > 0 && missing_kind_count() > 0) for {populated:?}",
            );
        }
    }

    /// MULTIPLICITY pin — a slice carrying the SAME [`ConditionKind`]
    /// multiple times still returns `true` on
    /// `is_kind_partially_covered` on any `N ≥ 2` closed set
    /// (multiplicity is irrelevant — one distinct kind + N-1 missing).
    /// Complement of the empty-slice arm — the middle predicate collapses
    /// to non-emptiness of both the distinct SET and the missing SET.
    #[test]
    fn condition_slice_is_kind_partially_covered_ignores_multiplicity() {
        assert!(
            ConditionKind::ALL.len() >= 2,
            "test assumes ConditionKind::ALL has ≥ 2 variants",
        );
        for k in ConditionKind::ALL {
            let doubled: Vec<Condition> = vec![condition_with(k), condition_with(k)];
            assert!(
                doubled.as_slice().is_kind_partially_covered(),
                "slice carrying {k:?} twice must return true on is_kind_partially_covered (still 1 distinct + N-1 missing)",
            );
            let tripled: Vec<Condition> =
                vec![condition_with(k), condition_with(k), condition_with(k)];
            assert!(
                tripled.as_slice().is_kind_partially_covered(),
                "slice carrying {k:?} three times must return true on is_kind_partially_covered (still 1 distinct + N-1 missing)",
            );
        }
    }

    /// TRICHOTOMY PARTITION pin — EXACTLY ONE of `is_kind_empty`,
    /// `is_kind_partially_covered`, and `is_kind_saturated` returns
    /// `true` on any `N ≥ 1` closed set across every representative
    /// arrangement (empty, single-populated, near-saturated,
    /// saturated). Byte-for-byte peer of the tagged-union parent-state
    /// trichotomy `is_empty + is_partially_populated + is_saturated == 1`
    /// one struct-layer up. The most load-bearing composition law on
    /// the closed-set partition — a regression that broke ONE arm
    /// (leaving the other two intact) surfaces HERE at ONE substrate
    /// test rather than as silent skew at the classifier callsite.
    #[test]
    fn condition_slice_partition_trichotomy_holds_on_every_arrangement() {
        assert!(
            ConditionKind::ALL.len() >= 2,
            "test assumes ConditionKind::ALL has ≥ 2 variants",
        );
        // Empty arm.
        let empty: &[Condition] = &[];
        assert_eq!(
            usize::from(empty.is_kind_empty())
                + usize::from(empty.is_kind_partially_covered())
                + usize::from(empty.is_kind_saturated()),
            1,
            "trichotomy partition violated on empty slice",
        );
        // Single-populated arm.
        for k in ConditionKind::ALL {
            let slice = [condition_with(k)];
            assert_eq!(
                usize::from(slice.is_kind_empty())
                    + usize::from(slice.is_kind_partially_covered())
                    + usize::from(slice.is_kind_saturated()),
                1,
                "trichotomy partition violated on single-populated slice with {k:?}",
            );
        }
        // Saturated arm.
        let saturated: Vec<Condition> =
            ConditionKind::ALL.into_iter().map(condition_with).collect();
        assert_eq!(
            usize::from(saturated.as_slice().is_kind_empty())
                + usize::from(saturated.as_slice().is_kind_partially_covered())
                + usize::from(saturated.as_slice().is_kind_saturated()),
            1,
            "trichotomy partition violated on saturated slice",
        );
        // Near-saturated arm (every kind except one) — meaningful on N ≥ 2.
        for omit in ConditionKind::ALL {
            let near_sat: Vec<Condition> = ConditionKind::ALL
                .into_iter()
                .filter(|k| *k != omit)
                .map(condition_with)
                .collect();
            assert_eq!(
                usize::from(near_sat.as_slice().is_kind_empty())
                    + usize::from(near_sat.as_slice().is_kind_partially_covered())
                    + usize::from(near_sat.as_slice().is_kind_saturated()),
                1,
                "trichotomy partition violated on near-saturated slice omitting {omit:?}",
            );
        }
    }

    // ── ConditionSliceExt::has_any_missing_kind — at-least-one halfspace pins ──
    //
    // Boolean at-least-one halfspace peer of `is_kind_saturated`:
    // `has_any_missing_kind()` returns `true` iff AT LEAST ONE
    // `ConditionKind::ALL` variant appears zero times in the slice,
    // byte-for-byte with `!is_kind_saturated()` via the definitional
    // negation in the trait's default body. The composition laws
    // `has_any_missing_kind() == !is_kind_saturated()`,
    // `has_any_missing_kind() == (missing_kind_count() > 0)`, and
    // `has_any_missing_kind() == !missing_kinds().is_empty()` are
    // pinned as the at-least-one halfspace arm of
    // `assert_slice_refinement_composition_laws`. Byte-for-byte peer
    // of `crate::tagged_union::TaggedUnion::has_any_missing_kind` one
    // struct-layer up under the SAME `!is_saturated` definitional
    // negation shape.

    /// EMPTY-SLICE pin — an empty slice returns `true` on
    /// `has_any_missing_kind` (every kind is missing, so at least one
    /// is). Dual of the empty-slice arm on `is_kind_saturated` (which
    /// returns `false`).
    #[test]
    fn condition_slice_has_any_missing_kind_returns_true_on_empty_slice() {
        let empty: &[Condition] = &[];
        assert!(
            empty.has_any_missing_kind(),
            "empty slice must return true on has_any_missing_kind",
        );
        assert_eq!(
            empty.has_any_missing_kind(),
            !empty.is_kind_saturated(),
            "empty has_any_missing_kind must equal !is_kind_saturated()",
        );
        assert_eq!(
            empty.has_any_missing_kind(),
            empty.missing_kind_count() > 0,
            "empty has_any_missing_kind must equal (missing_kind_count() > 0)",
        );
    }

    /// SINGLE-KIND pin — a slice populating exactly one variant
    /// returns `true` on any `ConditionKind::ALL` closed set with
    /// `N ≥ 2` (the other `N - 1` variants are missing).
    #[test]
    fn condition_slice_has_any_missing_kind_returns_true_on_single_kind_slice() {
        assert!(
            ConditionKind::ALL.len() >= 2,
            "test assumes ConditionKind::ALL has ≥ 2 variants",
        );
        for populated in ConditionKind::ALL {
            let slice = [condition_with(populated)];
            assert!(
                slice.has_any_missing_kind(),
                "single-populated slice with {populated:?} must return true on has_any_missing_kind",
            );
            assert_eq!(
                slice.has_any_missing_kind(),
                !slice.is_kind_saturated(),
                "single-populated has_any_missing_kind must equal !is_kind_saturated() for {populated:?}",
            );
        }
    }

    /// FULL-COVERAGE pin — a slice that carries every
    /// [`ConditionKind`] variant returns `false` on
    /// `has_any_missing_kind` — the SOLE arm where the primitive
    /// returns `false`, byte-for-byte peer of the SOLE arm on which
    /// `is_kind_saturated` returns `true`.
    #[test]
    fn condition_slice_has_any_missing_kind_returns_false_on_saturated_slice() {
        let saturated: Vec<Condition> =
            ConditionKind::ALL.into_iter().map(condition_with).collect();
        assert!(
            !saturated.as_slice().has_any_missing_kind(),
            "slice containing every ConditionKind must return false on has_any_missing_kind",
        );
        assert_eq!(
            saturated.as_slice().has_any_missing_kind(),
            !saturated.as_slice().is_kind_saturated(),
            "saturated has_any_missing_kind must equal !is_kind_saturated()",
        );
        assert_eq!(
            saturated.as_slice().has_any_missing_kind(),
            !saturated.as_slice().missing_kinds().is_empty(),
            "saturated has_any_missing_kind must equal !missing_kinds().is_empty()",
        );
    }

    /// DUPLICATE-COVERAGE pin — a slice that carries every
    /// [`ConditionKind`] variant multiple times still returns `false`
    /// (multiplicity is irrelevant to the at-least-one halfspace
    /// predicate on the closed-set-complement axis, byte-for-byte peer
    /// of the saturation-predicate arm).
    #[test]
    fn condition_slice_has_any_missing_kind_ignores_multiplicity() {
        let mut doubled: Vec<Condition> = Vec::new();
        for k in ConditionKind::ALL {
            doubled.push(condition_with(k));
            doubled.push(condition_with(k));
        }
        assert!(
            !doubled.as_slice().has_any_missing_kind(),
            "slice carrying every ConditionKind twice must return false on has_any_missing_kind",
        );
    }

    // ── ConditionSliceExt::has_unique_missing_kind — near-saturation-endpoint pins ─
    //
    // Boolean cardinality-mid-endpoint peer of `has_any_missing_kind`
    // on the closed-set-complement axis: `has_unique_missing_kind()`
    // returns `true` iff EXACTLY ONE ConditionKind::ALL variant
    // appears zero times in the slice. Default body is a two-step-
    // short-circuit walk over ConditionKind::ALL under a negated
    // `has_kind` predicate — pulls up to two hits off the filtered
    // iterator, returns `true` iff the first is Some and the second
    // is None. Short-circuits at the SECOND missing kind — strictly
    // cheaper than `missing_kind_count() == 1` (which walks every
    // slot) and `missing_kinds().len() == 1` (which allocates the
    // Vec) on every arm with ≥ 2 missing kinds. The composition laws
    // `has_unique_missing_kind() == (missing_kind_count() == 1)` and
    // `has_unique_missing_kind() == (missing_kinds().len() == 1)`
    // are pinned as the cardinality-mid-endpoint arm of
    // `assert_slice_refinement_composition_laws`. Byte-for-byte peer
    // of `crate::tagged_union::TaggedUnion::has_unique_missing_kind`
    // one struct-layer up under the SAME two-step short-circuit walk
    // shape.

    /// EMPTY-SLICE pin — an empty slice returns `false` on
    /// `has_unique_missing_kind` on any `N ≥ 2` closed set (every
    /// kind is missing — the fully-missing endpoint, `N` missing not
    /// `1`).
    #[test]
    fn condition_slice_has_unique_missing_kind_returns_false_on_empty_slice() {
        assert!(
            ConditionKind::ALL.len() >= 2,
            "test assumes ConditionKind::ALL has ≥ 2 variants",
        );
        let empty: &[Condition] = &[];
        assert!(
            !empty.has_unique_missing_kind(),
            "empty slice must return false on has_unique_missing_kind (all N kinds missing, not exactly 1)",
        );
        assert_eq!(
            empty.has_unique_missing_kind(),
            empty.missing_kind_count() == 1,
            "empty has_unique_missing_kind must equal (missing_kind_count() == 1)",
        );
    }

    /// SINGLE-KIND pin — a slice populating exactly one variant
    /// returns `false` on any `N ≥ 3` closed set (`N - 1 ≥ 2` kinds
    /// missing). On the degenerate `N == 2` closed set (which no
    /// production `ConditionKind` reaches; this workspace has
    /// `N == 8`) it would return `true`, so the pin gates on
    /// `N ≥ 3`.
    #[test]
    fn condition_slice_has_unique_missing_kind_returns_false_on_single_kind_slice() {
        if ConditionKind::ALL.len() < 3 {
            return;
        }
        for populated in ConditionKind::ALL {
            let slice = [condition_with(populated)];
            assert!(
                !slice.has_unique_missing_kind(),
                "single-populated slice with {populated:?} must return false on has_unique_missing_kind on N ≥ 3 closed sets ({} kinds missing, not exactly 1)",
                ConditionKind::ALL.len() - 1,
            );
            assert_eq!(
                slice.has_unique_missing_kind(),
                slice.missing_kind_count() == 1,
                "single-populated has_unique_missing_kind must equal (missing_kind_count() == 1) for {populated:?}",
            );
        }
    }

    /// NEAR-SATURATION-ENDPOINT pin — a slice carrying every
    /// [`ConditionKind`] EXCEPT exactly one returns `true` on
    /// `has_unique_missing_kind`. Sweeps ConditionKind::ALL; each
    /// arrangement omits one variant and populates the other `N - 1`.
    /// This is the SOLE arrangement where the primitive returns
    /// `true`. Also pins the widened composition law
    /// `has_unique_missing_kind() == (missing_kinds().len() == 1)`.
    #[test]
    fn condition_slice_has_unique_missing_kind_returns_true_on_near_saturation_endpoint() {
        for omitted in ConditionKind::ALL {
            let near_saturated: Vec<Condition> = ConditionKind::ALL
                .into_iter()
                .filter(|k| *k != omitted)
                .map(condition_with)
                .collect();
            let slice = near_saturated.as_slice();
            assert!(
                slice.has_unique_missing_kind(),
                "near-saturation-endpoint slice (omitting {omitted:?}) must return true on has_unique_missing_kind",
            );
            assert_eq!(
                slice.has_unique_missing_kind(),
                slice.missing_kind_count() == 1,
                "near-saturation-endpoint has_unique_missing_kind must equal (missing_kind_count() == 1) for omitted={omitted:?}",
            );
            assert_eq!(
                slice.has_unique_missing_kind(),
                slice.missing_kinds().len() == 1,
                "near-saturation-endpoint has_unique_missing_kind must equal (missing_kinds().len() == 1) for omitted={omitted:?}",
            );
            assert_eq!(
                slice.first_missing_kind(),
                Some(omitted),
                "near-saturation-endpoint first_missing_kind must name the SOLE remaining hole for omitted={omitted:?}",
            );
        }
    }

    /// SATURATED pin — a slice carrying every [`ConditionKind`]
    /// variant returns `false` on `has_unique_missing_kind` (zero
    /// missing, not exactly one). Dual of the SATURATED arm on
    /// `is_kind_saturated` which returns `true`. Also pins the
    /// composition law `has_unique_missing_kind() ==
    /// (missing_kind_count() == 1)` at zero-missing.
    #[test]
    fn condition_slice_has_unique_missing_kind_returns_false_on_saturated_slice() {
        let saturated: Vec<Condition> =
            ConditionKind::ALL.into_iter().map(condition_with).collect();
        assert!(
            !saturated.as_slice().has_unique_missing_kind(),
            "slice containing every ConditionKind must return false on has_unique_missing_kind (0 missing, not exactly 1)",
        );
        assert_eq!(
            saturated.as_slice().has_unique_missing_kind(),
            saturated.as_slice().missing_kind_count() == 1,
            "saturated has_unique_missing_kind must equal (missing_kind_count() == 1)",
        );
    }

    /// TWO-MISSING pin — a slice populating exactly `N - 2` variants
    /// returns `false` on `has_unique_missing_kind` (2 missing, not
    /// exactly 1). Pins the SECOND-slot short-circuit boundary — a
    /// regression that dropped the second-slot check (returning `true`
    /// on any partial-populated arm) surfaces HERE. Only meaningful
    /// on `N ≥ 2` closed sets.
    #[test]
    fn condition_slice_has_unique_missing_kind_returns_false_on_two_missing_slice() {
        assert!(
            ConditionKind::ALL.len() >= 2,
            "test assumes ConditionKind::ALL has ≥ 2 variants",
        );
        for i in 0..ConditionKind::ALL.len() {
            for j in (i + 1)..ConditionKind::ALL.len() {
                let two_missing: Vec<Condition> = ConditionKind::ALL
                    .into_iter()
                    .enumerate()
                    .filter(|(k, _)| *k != i && *k != j)
                    .map(|(_, k)| condition_with(k))
                    .collect();
                let slice = two_missing.as_slice();
                assert!(
                    !slice.has_unique_missing_kind(),
                    "two-missing slice (omitting index {i} and {j}) must return false on has_unique_missing_kind (2 missing, not exactly 1)",
                );
                assert_eq!(
                    slice.has_unique_missing_kind(),
                    slice.missing_kind_count() == 1,
                    "two-missing has_unique_missing_kind must equal (missing_kind_count() == 1) for omitted=({i}, {j})",
                );
            }
        }
    }

    /// MULTIPLICITY pin — a slice at the near-saturation-endpoint
    /// with each populated kind duplicated still returns `true`
    /// (multiplicity is irrelevant to the cardinality-mid-endpoint
    /// projection on the closed-set-complement axis, byte-for-byte
    /// peer of the saturation-predicate arm).
    #[test]
    fn condition_slice_has_unique_missing_kind_ignores_multiplicity() {
        for omitted in ConditionKind::ALL {
            let mut doubled: Vec<Condition> = Vec::new();
            for k in ConditionKind::ALL {
                if k != omitted {
                    doubled.push(condition_with(k));
                    doubled.push(condition_with(k));
                }
            }
            assert!(
                doubled.as_slice().has_unique_missing_kind(),
                "near-saturation-endpoint slice with each populated kind duplicated (omitting {omitted:?}) must return true on has_unique_missing_kind",
            );
        }
    }

    // ── ConditionSliceExt::has_multiple_missing_kinds — many-arm pins ──
    //
    // Boolean cardinality "≥ 2" many-arm peer of
    // `has_unique_missing_kind` on the closed-set-complement axis:
    // `has_multiple_missing_kinds()` returns `true` iff AT LEAST TWO
    // `ConditionKind::ALL` variants appear zero times in the slice.
    // Third and final arm of the {0, 1, ≥2} trichotomy on the missing
    // axis at the slice level (0-arm: `is_kind_saturated`; 1-arm:
    // `has_unique_missing_kind`; ≥ 2-arm: this primitive). Body
    // short-circuits at the second missing kind — strictly cheaper
    // than `missing_kind_count() >= 2` (which walks every slot) and
    // `missing_kinds().len() >= 2` (which allocates the Vec) on every
    // arm with ≥ 2 missing kinds. The composition laws
    // `has_multiple_missing_kinds() == (missing_kind_count() >= 2)`
    // and `has_multiple_missing_kinds() == (missing_kinds().len() >= 2)`
    // are pinned as the cardinality-many-arm arm of
    // `assert_slice_refinement_composition_laws`. Byte-for-byte peer
    // of `crate::tagged_union::TaggedUnion::has_multiple_missing_kinds`
    // one struct-layer up under the SAME two-step short-circuit walk
    // shape.

    /// EMPTY-SLICE pin — an empty slice returns `true` on
    /// `has_multiple_missing_kinds` on any `N ≥ 2` closed set (every
    /// kind is missing — the fully-missing endpoint, `N ≥ 2`
    /// missing).
    #[test]
    fn condition_slice_has_multiple_missing_kinds_returns_true_on_empty_slice() {
        assert!(
            ConditionKind::ALL.len() >= 2,
            "test assumes ConditionKind::ALL has ≥ 2 variants",
        );
        let empty: &[Condition] = &[];
        assert!(
            empty.has_multiple_missing_kinds(),
            "empty slice must return true on has_multiple_missing_kinds (all N ≥ 2 kinds missing)",
        );
        assert_eq!(
            empty.has_multiple_missing_kinds(),
            empty.missing_kind_count() >= 2,
            "empty has_multiple_missing_kinds must equal (missing_kind_count() >= 2)",
        );
    }

    /// SINGLE-KIND pin — a slice populating exactly one variant
    /// returns `true` on any `N ≥ 3` closed set (`N - 1 ≥ 2` kinds
    /// missing). On the degenerate `N == 2` closed set (which no
    /// production `ConditionKind` reaches; this workspace has
    /// `N == 8`) it would return `false`, so the pin gates on
    /// `N ≥ 3`.
    #[test]
    fn condition_slice_has_multiple_missing_kinds_returns_true_on_single_kind_slice() {
        if ConditionKind::ALL.len() < 3 {
            return;
        }
        for populated in ConditionKind::ALL {
            let slice = [condition_with(populated)];
            assert!(
                slice.has_multiple_missing_kinds(),
                "single-populated slice with {populated:?} must return true on has_multiple_missing_kinds on N ≥ 3 closed sets ({} kinds missing, ≥ 2)",
                ConditionKind::ALL.len() - 1,
            );
            assert_eq!(
                slice.has_multiple_missing_kinds(),
                slice.missing_kind_count() >= 2,
                "single-populated has_multiple_missing_kinds must equal (missing_kind_count() >= 2) for {populated:?}",
            );
        }
    }

    /// NEAR-SATURATION-ENDPOINT pin — a slice carrying every
    /// [`ConditionKind`] EXCEPT exactly one returns `false` on
    /// `has_multiple_missing_kinds` (exactly one missing, not ≥ 2).
    /// The SOLE-missing arrangement where the many-arm primitive
    /// returns `false` — the definitional boundary between the
    /// = 1 mid-endpoint and the ≥ 2 many-arm on the missing axis.
    /// Also pins the widened composition law
    /// `has_multiple_missing_kinds() == (missing_kinds().len() >= 2)`.
    #[test]
    fn condition_slice_has_multiple_missing_kinds_returns_false_on_near_saturation_endpoint() {
        for omitted in ConditionKind::ALL {
            let near_saturated: Vec<Condition> = ConditionKind::ALL
                .into_iter()
                .filter(|k| *k != omitted)
                .map(condition_with)
                .collect();
            let slice = near_saturated.as_slice();
            assert!(
                !slice.has_multiple_missing_kinds(),
                "near-saturation-endpoint slice (omitting {omitted:?}) must return false on has_multiple_missing_kinds (1 missing, not ≥ 2)",
            );
            assert_eq!(
                slice.has_multiple_missing_kinds(),
                slice.missing_kind_count() >= 2,
                "near-saturation-endpoint has_multiple_missing_kinds must equal (missing_kind_count() >= 2) for omitted={omitted:?}",
            );
            assert_eq!(
                slice.has_multiple_missing_kinds(),
                slice.missing_kinds().len() >= 2,
                "near-saturation-endpoint has_multiple_missing_kinds must equal (missing_kinds().len() >= 2) for omitted={omitted:?}",
            );
        }
    }

    /// SATURATED pin — a slice carrying every [`ConditionKind`]
    /// variant returns `false` on `has_multiple_missing_kinds` (zero
    /// missing, not ≥ 2). Dual of the SATURATED arm on
    /// `is_kind_saturated` which returns `true`. Also pins the
    /// composition law `has_multiple_missing_kinds() ==
    /// (missing_kind_count() >= 2)` at zero-missing.
    #[test]
    fn condition_slice_has_multiple_missing_kinds_returns_false_on_saturated_slice() {
        let saturated: Vec<Condition> =
            ConditionKind::ALL.into_iter().map(condition_with).collect();
        assert!(
            !saturated.as_slice().has_multiple_missing_kinds(),
            "slice containing every ConditionKind must return false on has_multiple_missing_kinds (0 missing, not ≥ 2)",
        );
        assert_eq!(
            saturated.as_slice().has_multiple_missing_kinds(),
            saturated.as_slice().missing_kind_count() >= 2,
            "saturated has_multiple_missing_kinds must equal (missing_kind_count() >= 2)",
        );
    }

    /// TWO-MISSING pin — a slice populating exactly `N - 2` variants
    /// returns `true` on `has_multiple_missing_kinds` (exactly 2
    /// missing, the SECOND-slot boundary of the ≥ 2 arm). Pins the
    /// second-slot short-circuit — a regression that dropped the
    /// second-slot check (returning `true` on any ≥ 1-missing arm,
    /// conflating with `has_any_missing_kind`) would still pass here,
    /// so this pin is complemented by the NEAR-SATURATION-ENDPOINT
    /// pin which distinguishes the =1 arm from the ≥ 2 arm.
    /// Only meaningful on `N ≥ 2` closed sets.
    #[test]
    fn condition_slice_has_multiple_missing_kinds_returns_true_on_two_missing_slice() {
        assert!(
            ConditionKind::ALL.len() >= 2,
            "test assumes ConditionKind::ALL has ≥ 2 variants",
        );
        for i in 0..ConditionKind::ALL.len() {
            for j in (i + 1)..ConditionKind::ALL.len() {
                let two_missing: Vec<Condition> = ConditionKind::ALL
                    .into_iter()
                    .enumerate()
                    .filter(|(k, _)| *k != i && *k != j)
                    .map(|(_, k)| condition_with(k))
                    .collect();
                let slice = two_missing.as_slice();
                assert!(
                    slice.has_multiple_missing_kinds(),
                    "two-missing slice (omitting index {i} and {j}) must return true on has_multiple_missing_kinds (2 missing, ≥ 2)",
                );
                assert_eq!(
                    slice.has_multiple_missing_kinds(),
                    slice.missing_kind_count() >= 2,
                    "two-missing has_multiple_missing_kinds must equal (missing_kind_count() >= 2) for omitted=({i}, {j})",
                );
            }
        }
    }

    /// MULTIPLICITY pin — a slice at the empty-endpoint duplicated
    /// remains empty (nothing to duplicate), while a slice at a
    /// K-populated arm with each populated kind duplicated still
    /// returns `true` on any `N ≥ K + 2` — multiplicity is
    /// irrelevant to the cardinality many-arm projection on the
    /// closed-set-complement axis, byte-for-byte peer of the
    /// saturation-predicate arm. Sweeps the near-two-missing
    /// arrangement (each pair-omitted arm, doubled populated) on
    /// `N ≥ 2` closed sets.
    #[test]
    fn condition_slice_has_multiple_missing_kinds_ignores_multiplicity() {
        assert!(
            ConditionKind::ALL.len() >= 2,
            "test assumes ConditionKind::ALL has ≥ 2 variants",
        );
        for i in 0..ConditionKind::ALL.len() {
            for j in (i + 1)..ConditionKind::ALL.len() {
                let mut doubled: Vec<Condition> = Vec::new();
                for (idx, kind) in ConditionKind::ALL.into_iter().enumerate() {
                    if idx != i && idx != j {
                        doubled.push(condition_with(kind));
                        doubled.push(condition_with(kind));
                    }
                }
                assert!(
                    doubled.as_slice().has_multiple_missing_kinds(),
                    "two-missing slice (omitting index {i} and {j}) with each populated kind duplicated must return true on has_multiple_missing_kinds",
                );
            }
        }
    }

    // ── ConditionSliceExt::has_at_most_one_missing_kind — "≤ 1" pins ─
    //
    // Boolean cardinality "≤ 1" negation peer of
    // `has_multiple_missing_kinds` on the closed-set-complement axis:
    // `has_at_most_one_missing_kind()` returns `true` iff AT MOST ONE
    // `ConditionKind::ALL` variant appears zero times in the slice.
    // Definitional negation of the many-arm primitive
    // (`!has_multiple_missing_kinds`), and trichotomy-union of the
    // zero-arm + one-arm primitives (`is_kind_saturated ||
    // has_unique_missing_kind`). Body short-circuits transitively
    // through the many-arm walk — strictly cheaper than
    // `missing_kind_count() <= 1` (which walks every slot) and
    // `missing_kinds().len() <= 1` (which allocates the Vec) on every
    // arm. The composition laws
    // `has_at_most_one_missing_kind() == !has_multiple_missing_kinds()`,
    // `has_at_most_one_missing_kind() == (missing_kind_count() <= 1)`,
    // `has_at_most_one_missing_kind() == (missing_kinds().len() <= 1)`,
    // and `has_at_most_one_missing_kind() == is_kind_saturated() ||
    // has_unique_missing_kind()` are pinned as the "≤ 1" arm of
    // `assert_slice_refinement_composition_laws`. Byte-for-byte peer
    // of `crate::tagged_union::TaggedUnion::has_at_most_one_missing_kind`
    // one struct-layer up under the SAME `!has_multiple_missing_kinds`
    // definitional negation shape.

    /// EMPTY-SLICE pin — an empty slice returns `false` on
    /// `has_at_most_one_missing_kind` on any `N ≥ 2` closed set
    /// (every kind is missing — `N ≥ 2` missing, not `≤ 1`). Dual of
    /// the empty-slice arm on `has_multiple_missing_kinds` which
    /// returns `true`.
    #[test]
    fn condition_slice_has_at_most_one_missing_kind_returns_false_on_empty_slice() {
        assert!(
            ConditionKind::ALL.len() >= 2,
            "test assumes ConditionKind::ALL has ≥ 2 variants",
        );
        let empty: &[Condition] = &[];
        assert!(
            !empty.has_at_most_one_missing_kind(),
            "empty slice must return false on has_at_most_one_missing_kind (all N ≥ 2 kinds missing, not ≤ 1)",
        );
        assert_eq!(
            empty.has_at_most_one_missing_kind(),
            empty.missing_kind_count() <= 1,
            "empty has_at_most_one_missing_kind must equal (missing_kind_count() <= 1)",
        );
    }

    /// SINGLE-KIND pin — a slice populating exactly one variant
    /// returns `false` on any `N ≥ 3` closed set (`N - 1 ≥ 2` kinds
    /// missing, not `≤ 1`). On the degenerate `N == 2` closed set it
    /// would return `true` (exactly 1 missing), so the pin gates on
    /// `N ≥ 3` — this workspace has `N == 8`.
    #[test]
    fn condition_slice_has_at_most_one_missing_kind_returns_false_on_single_kind_slice() {
        if ConditionKind::ALL.len() < 3 {
            return;
        }
        for populated in ConditionKind::ALL {
            let slice = [condition_with(populated)];
            assert!(
                !slice.has_at_most_one_missing_kind(),
                "single-populated slice with {populated:?} must return false on has_at_most_one_missing_kind on N ≥ 3 closed sets ({} kinds missing, not ≤ 1)",
                ConditionKind::ALL.len() - 1,
            );
            assert_eq!(
                slice.has_at_most_one_missing_kind(),
                slice.missing_kind_count() <= 1,
                "single-populated has_at_most_one_missing_kind must equal (missing_kind_count() <= 1) for {populated:?}",
            );
        }
    }

    /// NEAR-SATURATION-ENDPOINT pin — a slice carrying every
    /// [`ConditionKind`] EXCEPT exactly one returns `true` on
    /// `has_at_most_one_missing_kind` (exactly 1 missing, `≤ 1`).
    /// The `= 1` mid-endpoint arm of the trichotomy union — one of
    /// the two arrangement classes where the "≤ 1" primitive
    /// returns `true`. Also pins the widened composition laws
    /// `has_at_most_one_missing_kind() == (missing_kinds().len() <= 1)`
    /// and `has_at_most_one_missing_kind() == !has_multiple_missing_kinds()`
    /// and the trichotomy-union composition law
    /// `has_at_most_one_missing_kind() == is_kind_saturated() ||
    /// has_unique_missing_kind()`.
    #[test]
    fn condition_slice_has_at_most_one_missing_kind_returns_true_on_near_saturation_endpoint() {
        for omitted in ConditionKind::ALL {
            let near_saturated: Vec<Condition> = ConditionKind::ALL
                .into_iter()
                .filter(|k| *k != omitted)
                .map(condition_with)
                .collect();
            let slice = near_saturated.as_slice();
            assert!(
                slice.has_at_most_one_missing_kind(),
                "near-saturation-endpoint slice (omitting {omitted:?}) must return true on has_at_most_one_missing_kind (1 missing, ≤ 1)",
            );
            assert_eq!(
                slice.has_at_most_one_missing_kind(),
                !slice.has_multiple_missing_kinds(),
                "near-saturation-endpoint has_at_most_one_missing_kind must equal !has_multiple_missing_kinds() for omitted={omitted:?}",
            );
            assert_eq!(
                slice.has_at_most_one_missing_kind(),
                slice.missing_kind_count() <= 1,
                "near-saturation-endpoint has_at_most_one_missing_kind must equal (missing_kind_count() <= 1) for omitted={omitted:?}",
            );
            assert_eq!(
                slice.has_at_most_one_missing_kind(),
                slice.missing_kinds().len() <= 1,
                "near-saturation-endpoint has_at_most_one_missing_kind must equal (missing_kinds().len() <= 1) for omitted={omitted:?}",
            );
            assert_eq!(
                slice.has_at_most_one_missing_kind(),
                slice.is_kind_saturated() || slice.has_unique_missing_kind(),
                "near-saturation-endpoint has_at_most_one_missing_kind must equal (is_kind_saturated() || has_unique_missing_kind()) for omitted={omitted:?}",
            );
        }
    }

    /// SATURATED pin — a slice carrying every [`ConditionKind`]
    /// variant returns `true` on `has_at_most_one_missing_kind` (0
    /// missing, `≤ 1`). The `= 0` zero-arm of the trichotomy union
    /// — the OTHER arrangement class where the "≤ 1" primitive
    /// returns `true`. Dual of the SATURATED arm on
    /// `has_multiple_missing_kinds` which returns `false`.
    #[test]
    fn condition_slice_has_at_most_one_missing_kind_returns_true_on_saturated_slice() {
        let saturated: Vec<Condition> =
            ConditionKind::ALL.into_iter().map(condition_with).collect();
        assert!(
            saturated.as_slice().has_at_most_one_missing_kind(),
            "slice containing every ConditionKind must return true on has_at_most_one_missing_kind (0 missing, ≤ 1)",
        );
        assert_eq!(
            saturated.as_slice().has_at_most_one_missing_kind(),
            saturated.as_slice().missing_kind_count() <= 1,
            "saturated has_at_most_one_missing_kind must equal (missing_kind_count() <= 1)",
        );
        assert_eq!(
            saturated.as_slice().has_at_most_one_missing_kind(),
            saturated.as_slice().is_kind_saturated()
                || saturated.as_slice().has_unique_missing_kind(),
            "saturated has_at_most_one_missing_kind must equal (is_kind_saturated() || has_unique_missing_kind())",
        );
    }

    /// TWO-MISSING pin — a slice populating exactly `N - 2` variants
    /// returns `false` on `has_at_most_one_missing_kind` (exactly 2
    /// missing, not `≤ 1`). The SECOND-slot boundary between the
    /// "≤ 1" arm and the "≥ 2" arm — a regression that dropped the
    /// negation (returning `has_multiple_missing_kinds` itself),
    /// swapped the wrong side, or drifted the trichotomy union
    /// operator from `||` to `&&` surfaces HERE.
    #[test]
    fn condition_slice_has_at_most_one_missing_kind_returns_false_on_two_missing_slice() {
        assert!(
            ConditionKind::ALL.len() >= 2,
            "test assumes ConditionKind::ALL has ≥ 2 variants",
        );
        for i in 0..ConditionKind::ALL.len() {
            for j in (i + 1)..ConditionKind::ALL.len() {
                let two_missing: Vec<Condition> = ConditionKind::ALL
                    .into_iter()
                    .enumerate()
                    .filter(|(k, _)| *k != i && *k != j)
                    .map(|(_, k)| condition_with(k))
                    .collect();
                let slice = two_missing.as_slice();
                assert!(
                    !slice.has_at_most_one_missing_kind(),
                    "two-missing slice (omitting index {i} and {j}) must return false on has_at_most_one_missing_kind (2 missing, not ≤ 1)",
                );
                assert_eq!(
                    slice.has_at_most_one_missing_kind(),
                    slice.missing_kind_count() <= 1,
                    "two-missing has_at_most_one_missing_kind must equal (missing_kind_count() <= 1) for omitted=({i}, {j})",
                );
            }
        }
    }

    /// MULTIPLICITY pin — a slice at a K-populated arm with each
    /// populated kind duplicated still returns the same "≤ 1"
    /// Boolean as its single-copy peer — multiplicity is irrelevant
    /// to the cardinality "≤ 1" projection on the closed-set-
    /// complement axis, byte-for-byte peer of
    /// `has_multiple_missing_kinds`'s multiplicity behavior.
    #[test]
    fn condition_slice_has_at_most_one_missing_kind_ignores_multiplicity() {
        // Near-saturation arm doubled — every populated kind
        // doubled, exactly one variant omitted; still returns true.
        for omitted in ConditionKind::ALL {
            let mut doubled: Vec<Condition> = Vec::new();
            for k in ConditionKind::ALL {
                if k != omitted {
                    doubled.push(condition_with(k));
                    doubled.push(condition_with(k));
                }
            }
            assert!(
                doubled.as_slice().has_at_most_one_missing_kind(),
                "near-saturation slice (omitting {omitted:?}) with each populated kind duplicated must return true on has_at_most_one_missing_kind",
            );
        }
    }

    // ── ConditionSliceExt::lacks_kind — per-kind complement pins ──────
    //
    // Boolean per-kind closed-set-complement peer of `has_kind`:
    // `lacks_kind(k)` returns `true` iff NO Condition in the slice
    // carries the addressed kind, byte-for-byte with `!has_kind(k)`
    // via the definitional negation in the trait's default body.
    // The composition laws `lacks_kind(k) == !has_kind(k)` and
    // `lacks_kind(k) == missing_kinds().contains(&k)` are pinned as
    // the per-kind-complement arm of
    // `assert_slice_refinement_composition_laws`. Byte-for-byte peer
    // of `crate::tagged_union::TaggedUnion::lacks` one struct-layer up
    // under the SAME `!has(kind)` definitional negation shape.

    /// EMPTY-SLICE pin — an empty slice returns `true` for every
    /// [`ConditionKind`] on `lacks_kind` (no kind appears, so every
    /// kind is lacked). Dual of the empty-slice arm on `has_kind`
    /// (which returns `false` for every kind). Sweeps
    /// [`ConditionKind::ALL`] so a regression that dropped the
    /// negation, returned `false` (the has-kind identity on empty),
    /// or drifted to a per-kind constant surfaces HERE.
    #[test]
    fn condition_slice_lacks_kind_returns_true_on_empty_slice_for_every_kind() {
        let empty: &[Condition] = &[];
        for kind in ConditionKind::ALL {
            assert!(
                empty.lacks_kind(kind),
                "empty slice must return true on lacks_kind for {kind:?}",
            );
            assert_eq!(
                empty.lacks_kind(kind),
                !empty.has_kind(kind),
                "empty lacks_kind must equal !has_kind for {kind:?}",
            );
        }
    }

    /// SINGLE-KIND pin — a slice with EXACTLY ONE `Condition` carrying
    /// the addressed kind returns `false` on `lacks_kind` for the
    /// populated kind and `true` for every OTHER kind. Sweeps
    /// [`ConditionKind::ALL`] × [`ConditionKind::ALL`] so a regression
    /// that swapped the wrong side, drifted the negation, or drifted
    /// the walk from `has_kind` surfaces HERE. Also pins the
    /// composition law `lacks_kind(k) == !has_kind(k)` per-kind.
    #[test]
    fn condition_slice_lacks_kind_returns_true_on_every_missing_kind() {
        for populated in ConditionKind::ALL {
            let slice = [condition_with(populated)];
            for probe in ConditionKind::ALL {
                let expected_lacks = probe != populated;
                assert_eq!(
                    slice.as_slice().lacks_kind(probe),
                    expected_lacks,
                    "single-populated slice with {populated:?} must return {expected_lacks} on lacks_kind({probe:?})",
                );
                assert_eq!(
                    slice.as_slice().lacks_kind(probe),
                    !slice.as_slice().has_kind(probe),
                    "single-populated lacks_kind({probe:?}) must equal !has_kind({probe:?}) for populated={populated:?}",
                );
            }
        }
    }

    /// SATURATED pin — a slice carrying every [`ConditionKind`] variant
    /// returns `false` on `lacks_kind` for every arm (the SOLE
    /// arrangement where the primitive returns `false` for every kind).
    /// Dual of the SATURATED arm on `is_kind_saturated` which returns
    /// `true`. Pins the composition law `lacks_kind(k) ==
    /// missing_kinds().contains(&k)` per-kind against the empty missing
    /// set.
    #[test]
    fn condition_slice_lacks_kind_returns_false_on_saturated_slice_for_every_kind() {
        let saturated: Vec<Condition> =
            ConditionKind::ALL.into_iter().map(condition_with).collect();
        let missing = saturated.as_slice().missing_kinds();
        for kind in ConditionKind::ALL {
            assert!(
                !saturated.as_slice().lacks_kind(kind),
                "saturated slice must return false on lacks_kind for {kind:?}",
            );
            assert_eq!(
                saturated.as_slice().lacks_kind(kind),
                missing.contains(&kind),
                "saturated lacks_kind({kind:?}) must equal missing_kinds().contains(&{kind:?})",
            );
        }
    }

    /// MULTIPLICITY pin — a slice carrying the addressed kind multiple
    /// times still returns `false` on `lacks_kind` for that kind
    /// (multiplicity is irrelevant to the per-kind Boolean-complement
    /// projection on the closed-set-complement axis, byte-for-byte
    /// with `has_kind`'s multiplicity behavior).
    #[test]
    fn condition_slice_lacks_kind_ignores_multiplicity_on_the_populated_side() {
        for populated in ConditionKind::ALL {
            let slice = [
                condition_with(populated),
                condition_with(populated),
                condition_with(populated),
            ];
            assert!(
                !slice.as_slice().lacks_kind(populated),
                "duplicate-populated slice with {populated:?} must return false on lacks_kind for {populated:?}",
            );
        }
    }

    // ── ConditionSliceExt::has_only_kind — kind-scoped strict-refinement pins ─
    //
    // Boolean `(kind, "AND no other kind")` refinement of the closed-
    // set-inversion widened primitive `distinct_kinds`:
    // `has_only_kind(k)` returns `true` iff `k` is the SOLE distinct
    // populated kind AND appears at least once. Fused-walk over
    // `ConditionKind::ALL` under `has_kind` — strictly cheaper than
    // reaching for either `has_kind(k) && distinct_kind_count() == 1`
    // or `distinct_kinds() == vec![k]` composition on every arm where
    // a second kind lives alongside `k`. The composition law
    // `has_only_kind(k) == (distinct_kinds() == vec![k])` is pinned
    // as the kind-scoped strict-refinement arm of
    // `assert_slice_refinement_composition_laws`. Byte-for-byte peer
    // of `crate::tagged_union::TaggedUnion::has_only` one struct-layer
    // up under the SAME fused short-circuit closed-set walk shape.

    /// EMPTY-SLICE pin — an empty slice returns `false` on
    /// `has_only_kind` for every arm (no kind is populated, so no
    /// kind is "only"). Pins the composition law `has_only_kind(k)
    /// == (distinct_kinds() == vec![k])` on the zero-distinct
    /// arrangement's empty distinct-set: `[] != vec![k]` for every k,
    /// so both sides yield `false`.
    #[test]
    fn condition_slice_has_only_kind_returns_false_on_empty_slice() {
        let empty: &[Condition] = &[];
        for kind in ConditionKind::ALL {
            assert!(
                !empty.has_only_kind(kind),
                "empty slice must return false on has_only_kind for {kind:?}",
            );
            assert_eq!(
                empty.has_only_kind(kind),
                empty.distinct_kinds() == vec![kind],
                "empty has_only_kind({kind:?}) must equal (distinct_kinds() == vec![{kind:?}])",
            );
        }
    }

    /// SINGLE-KIND pin — a slice with EXACTLY ONE `Condition` carrying
    /// the addressed kind returns `true` on `has_only_kind` for the
    /// populated kind and `false` for every OTHER kind. Sweeps
    /// [`ConditionKind::ALL`] × [`ConditionKind::ALL`] so a regression
    /// that swapped the wrong side, drifted the fused walk, or
    /// confused the strict-refinement axis with the point-probe axis
    /// (returning `has_kind` — TOO LOOSE) surfaces HERE. Also pins the
    /// composition law `has_only_kind(k) == (distinct_kinds() ==
    /// vec![k])` per-kind against the singleton distinct-set.
    #[test]
    fn condition_slice_has_only_kind_returns_true_on_single_populated_kind() {
        for populated in ConditionKind::ALL {
            let slice = [condition_with(populated)];
            for probe in ConditionKind::ALL {
                let expected = probe == populated;
                assert_eq!(
                    slice.as_slice().has_only_kind(probe),
                    expected,
                    "single-populated slice with {populated:?} must return {expected} on has_only_kind({probe:?})",
                );
                assert_eq!(
                    slice.as_slice().has_only_kind(probe),
                    slice.as_slice().distinct_kinds() == vec![probe],
                    "single-populated has_only_kind({probe:?}) must equal (distinct_kinds() == vec![{probe:?}]) for populated={populated:?}",
                );
            }
        }
    }

    /// MULTIPLICITY pin — a slice carrying the addressed kind multiple
    /// times still returns `true` on `has_only_kind` for that kind
    /// (multiplicity is irrelevant to the kind-scoped strict-
    /// refinement projection on the closed-set-inversion axis, byte-
    /// for-byte with `has_kind`'s multiplicity behavior). Pins that
    /// the fused walk under `has_kind` inherits the multiplicity-blind
    /// semantics without a special-case on the count.
    #[test]
    fn condition_slice_has_only_kind_ignores_multiplicity_on_the_populated_side() {
        for populated in ConditionKind::ALL {
            let slice = [
                condition_with(populated),
                condition_with(populated),
                condition_with(populated),
            ];
            for probe in ConditionKind::ALL {
                let expected = probe == populated;
                assert_eq!(
                    slice.as_slice().has_only_kind(probe),
                    expected,
                    "duplicate-populated slice with {populated:?} must return {expected} on has_only_kind({probe:?})",
                );
            }
        }
    }

    /// TWO-KINDS pin — a slice carrying two DIFFERENT kinds returns
    /// `false` on `has_only_kind` for EVERY arm (the "some other kind
    /// is present" clause fails at the fused walk's earliest step
    /// that hits the second kind, regardless of which kind is
    /// addressed). Sweeps [`ConditionKind::ALL`] × [`ConditionKind::ALL`]
    /// (skipping equal pairs since a two-distinct-kinds slice requires
    /// `p != q`) so a regression that dropped the fused walk's early-
    /// exit surfaces at every off-diagonal (p, q) pair.
    #[test]
    fn condition_slice_has_only_kind_returns_false_on_two_kinds_slice() {
        for p in ConditionKind::ALL {
            for q in ConditionKind::ALL {
                if p == q {
                    continue;
                }
                let slice = [condition_with(p), condition_with(q)];
                for probe in ConditionKind::ALL {
                    assert!(
                        !slice.as_slice().has_only_kind(probe),
                        "two-kinds slice with {{{p:?}, {q:?}}} must return false on has_only_kind for {probe:?}",
                    );
                }
            }
        }
    }

    /// SATURATED pin — a slice carrying every [`ConditionKind`] variant
    /// returns `false` on `has_only_kind` for every arm (N distinct
    /// kinds populate, so no single kind is "only"). Dual of the
    /// SATURATED arm on `is_kind_saturated` which returns `true` for
    /// the SAME arrangement. Pins the composition law `has_only_kind(k)
    /// == (has_kind(k) && distinct_kind_count() == 1)` per-kind against
    /// the saturated `distinct_kind_count() == N`.
    #[test]
    fn condition_slice_has_only_kind_returns_false_on_saturated_slice() {
        let saturated: Vec<Condition> =
            ConditionKind::ALL.into_iter().map(condition_with).collect();
        for kind in ConditionKind::ALL {
            assert!(
                !saturated.as_slice().has_only_kind(kind),
                "saturated slice must return false on has_only_kind for {kind:?}",
            );
            assert_eq!(
                saturated.as_slice().has_only_kind(kind),
                saturated.as_slice().has_kind(kind)
                    && saturated.as_slice().distinct_kind_count() == 1,
                "saturated has_only_kind({kind:?}) must equal (has_kind && distinct_kind_count == 1)",
            );
        }
    }

    // ── ConditionSliceExt::lacks_only_kind — kind-scoped strict-
    // refinement on the closed-set-complement (missing) axis ─
    //
    // Byte-for-byte peer of `has_only_kind` under complement: fused
    // short-circuit walk over `ConditionKind::ALL` under `has_kind`
    // that skips populated slots, returns `false` at the earliest
    // missing slot whose kind is NOT `kind`, and returns `true` iff
    // the sweep completes with `kind` seen as the sole missing slot.
    // The composition laws
    // `lacks_only_kind(k) == (missing_kinds() == vec![k])` and
    // `lacks_only_kind(k) == (lacks_kind(k) && missing_kind_count() == 1)`
    // are pinned as the closed-set-complement kind-scoped strict-
    // refinement arms of `assert_slice_refinement_composition_laws`.

    /// EMPTY-SLICE pin — every kind is missing (missing set == ALL),
    /// so no kind is "only" missing on any `N ≥ 2` closed set. Returns
    /// `false` on every arm.
    #[test]
    fn condition_slice_lacks_only_kind_returns_false_on_empty_slice() {
        let empty: &[Condition] = &[];
        for kind in ConditionKind::ALL {
            assert!(
                !empty.lacks_only_kind(kind),
                "empty slice must return false on lacks_only_kind for {kind:?}",
            );
            assert_eq!(
                empty.lacks_only_kind(kind),
                empty.missing_kinds() == vec![kind],
                "empty lacks_only_kind({kind:?}) must equal (missing_kinds() == vec![{kind:?}])",
            );
        }
    }

    /// NEAR-SATURATION pin — a slice covering every kind except one
    /// returns `true` on `lacks_only_kind(omitted)` and `false` on
    /// every other kind. The sole `true` arm on the well-formed
    /// missing diagonal.
    #[test]
    fn condition_slice_lacks_only_kind_returns_true_on_near_saturation_slice() {
        for omitted in ConditionKind::ALL {
            let slice: Vec<Condition> = ConditionKind::ALL
                .into_iter()
                .filter(|k| *k != omitted)
                .map(condition_with)
                .collect();
            for kind in ConditionKind::ALL {
                let expected = kind == omitted;
                assert_eq!(
                    slice.as_slice().lacks_only_kind(kind),
                    expected,
                    "near-saturation slice omitted={omitted:?} must return {expected} on lacks_only_kind for {kind:?}",
                );
                assert_eq!(
                    slice.as_slice().lacks_only_kind(kind),
                    slice.as_slice().missing_kinds() == vec![kind],
                    "near-saturation lacks_only_kind({kind:?}) must equal (missing_kinds() == vec![{kind:?}]) for omitted={omitted:?}",
                );
            }
        }
    }

    /// MULTIPLICITY pin — a slice carrying every kind except one, with
    /// the populated kinds each duplicated, ignores multiplicity on
    /// the populated side (byte-for-byte with `has_kind`'s multiplicity
    /// behavior). Returns `true` on `lacks_only_kind(omitted)`.
    #[test]
    fn condition_slice_lacks_only_kind_ignores_multiplicity_on_the_populated_side() {
        for omitted in ConditionKind::ALL {
            let mut slice: Vec<Condition> = Vec::new();
            for k in ConditionKind::ALL {
                if k != omitted {
                    slice.push(condition_with(k));
                    slice.push(condition_with(k));
                }
            }
            for kind in ConditionKind::ALL {
                let expected = kind == omitted;
                assert_eq!(
                    slice.as_slice().lacks_only_kind(kind),
                    expected,
                    "duplicate-populated near-saturation slice omitted={omitted:?} must return {expected} on lacks_only_kind for {kind:?}",
                );
            }
        }
    }

    /// TWO-MISSING pin — a slice omitting exactly two kinds returns
    /// `false` on every arm; the strict refinement fails at the
    /// earliest walk step that hits the second missing kind. On
    /// `ConditionKind::ALL` of cardinality `N`, `N ≥ 3` is required
    /// for a two-missing arrangement to exist.
    #[test]
    fn condition_slice_lacks_only_kind_returns_false_on_two_missing_slice() {
        assert!(
            ConditionKind::ALL.len() >= 3,
            "two-missing arrangement requires N ≥ 3",
        );
        // Slice carries every kind except the first two of ALL.
        let slice: Vec<Condition> = ConditionKind::ALL
            .into_iter()
            .skip(2)
            .map(condition_with)
            .collect();
        for kind in ConditionKind::ALL {
            assert!(
                !slice.as_slice().lacks_only_kind(kind),
                "two-missing slice must return false on lacks_only_kind for {kind:?}",
            );
            assert_eq!(
                slice.as_slice().lacks_only_kind(kind),
                slice.as_slice().missing_kinds() == vec![kind],
                "two-missing lacks_only_kind({kind:?}) must equal (missing_kinds() == vec![{kind:?}])",
            );
        }
    }

    /// SATURATED pin — every kind populated, no kind missing, no kind
    /// is "only" missing. Returns `false` on every arm.
    #[test]
    fn condition_slice_lacks_only_kind_returns_false_on_saturated_slice() {
        let saturated: Vec<Condition> =
            ConditionKind::ALL.into_iter().map(condition_with).collect();
        for kind in ConditionKind::ALL {
            assert!(
                !saturated.as_slice().lacks_only_kind(kind),
                "saturated slice must return false on lacks_only_kind for {kind:?}",
            );
            assert_eq!(
                saturated.as_slice().lacks_only_kind(kind),
                saturated.as_slice().lacks_kind(kind)
                    && saturated.as_slice().missing_kind_count() == 1,
                "saturated lacks_only_kind({kind:?}) must equal (lacks_kind && missing_kind_count == 1)",
            );
        }
    }

    // ── ConditionSliceExt::first_distinct_kind — earliest-element pins ─
    //
    // Short-circuiting Option<ConditionKind> peer of the closed-set-
    // inversion widened primitive `distinct_kinds`: `first_distinct_kind()`
    // returns the earliest present kind in canonical ConditionKind::ALL
    // order without materializing the intermediate Vec<ConditionKind>.
    // The composition law `first_distinct_kind() == distinct_kinds()
    // .first().copied()` is pinned as the earliest-element-inversion arm
    // of `assert_slice_refinement_composition_laws`.

    /// EMPTY-SLICE pin — an empty slice returns `None` on
    /// `first_distinct_kind`, byte-for-byte with
    /// `distinct_kinds().first().copied()`.
    #[test]
    fn condition_slice_first_distinct_kind_returns_none_on_empty_slice() {
        let empty: &[Condition] = &[];
        assert_eq!(
            empty.first_distinct_kind(),
            None,
            "empty slice must return None on first_distinct_kind",
        );
        assert_eq!(
            empty.first_distinct_kind(),
            empty.distinct_kinds().first().copied(),
            "empty first_distinct_kind must equal distinct_kinds().first().copied()",
        );
    }

    /// PER-VARIANT pin — a slice with EXACTLY ONE `Condition` carrying
    /// the addressed kind returns `Some(that_kind)` on
    /// `first_distinct_kind`.
    #[test]
    fn condition_slice_first_distinct_kind_returns_populated_variant() {
        for populated in ConditionKind::ALL {
            let slice = [condition_with(populated)];
            assert_eq!(
                slice.first_distinct_kind(),
                Some(populated),
                "single-populated slice must return Some({populated:?}) on first_distinct_kind",
            );
            assert_eq!(
                slice.first_distinct_kind(),
                slice.distinct_kinds().first().copied(),
                "single-populated first_distinct_kind must equal distinct_kinds().first().copied() for {populated:?}",
            );
        }
    }

    /// FULL-COVERAGE pin — a slice that carries every [`ConditionKind`]
    /// variant returns `Some(ConditionKind::ALL[0])` on
    /// `first_distinct_kind` (the first ALL entry hits at the earliest
    /// walk step).
    #[test]
    fn condition_slice_first_distinct_kind_returns_first_all_on_saturated_slice() {
        let saturated: Vec<Condition> =
            ConditionKind::ALL.into_iter().map(condition_with).collect();
        assert_eq!(
            saturated.as_slice().first_distinct_kind(),
            Some(ConditionKind::ALL[0]),
            "saturated slice must return Some(ConditionKind::ALL[0]) on first_distinct_kind",
        );
        assert_eq!(
            saturated.as_slice().first_distinct_kind(),
            saturated.as_slice().distinct_kinds().first().copied(),
            "saturated first_distinct_kind must equal distinct_kinds().first().copied()",
        );
    }

    // ── ConditionSliceExt::first_missing_kind — earliest-element pins ──

    /// EMPTY-SLICE pin — an empty slice returns
    /// `Some(ConditionKind::ALL[0])` on `first_missing_kind` (every
    /// kind missing, first hit is index 0). Dual of the empty-slice arm
    /// on `first_distinct_kind` which returns `None`.
    #[test]
    fn condition_slice_first_missing_kind_returns_first_all_on_empty_slice() {
        let empty: &[Condition] = &[];
        assert_eq!(
            empty.first_missing_kind(),
            Some(ConditionKind::ALL[0]),
            "empty slice must return Some(ConditionKind::ALL[0]) on first_missing_kind",
        );
        assert_eq!(
            empty.first_missing_kind(),
            empty.missing_kinds().first().copied(),
            "empty first_missing_kind must equal missing_kinds().first().copied()",
        );
    }

    /// PER-VARIANT pin — a slice populating exactly `k` returns
    /// `Some(ALL[0])` if `k != ALL[0]`, else `Some(ALL[1])` (the earliest
    /// non-`k` entry).
    #[test]
    fn condition_slice_first_missing_kind_returns_earliest_absent_variant() {
        for populated in ConditionKind::ALL {
            let slice = [condition_with(populated)];
            let expected = ConditionKind::ALL.into_iter().find(|k| *k != populated);
            assert_eq!(
                slice.first_missing_kind(),
                expected,
                "single-populated slice must return earliest ALL entry != {populated:?} on first_missing_kind",
            );
            assert_eq!(
                slice.first_missing_kind(),
                slice.missing_kinds().first().copied(),
                "single-populated first_missing_kind must equal missing_kinds().first().copied() for {populated:?}",
            );
        }
    }

    /// FULL-COVERAGE pin — a slice that carries every [`ConditionKind`]
    /// variant returns `None` on `first_missing_kind` (no kind missing).
    #[test]
    fn condition_slice_first_missing_kind_returns_none_on_saturated_slice() {
        let saturated: Vec<Condition> =
            ConditionKind::ALL.into_iter().map(condition_with).collect();
        assert_eq!(
            saturated.as_slice().first_missing_kind(),
            None,
            "saturated slice must return None on first_missing_kind",
        );
        assert_eq!(
            saturated.as_slice().first_missing_kind(),
            saturated.as_slice().missing_kinds().first().copied(),
            "saturated first_missing_kind must equal missing_kinds().first().copied()",
        );
    }

    // ── ConditionSliceExt::last_distinct_kind — latest-element pins ────
    //
    // Short-circuiting Option<ConditionKind> peer of the closed-set-
    // inversion widened primitive `distinct_kinds` on the LATEST-hit
    // side: `last_distinct_kind()` returns the latest present kind in
    // canonical ConditionKind::ALL order via a REVERSED walk with no
    // intermediate Vec<ConditionKind> allocation. The composition law
    // `last_distinct_kind() == distinct_kinds().last().copied()` is
    // pinned as the latest-element-inversion arm of
    // `assert_slice_refinement_composition_laws`.

    /// EMPTY-SLICE pin — an empty slice returns `None` on
    /// `last_distinct_kind`, byte-for-byte with
    /// `distinct_kinds().last().copied()` (both scalar endpoints agree
    /// on emptiness).
    #[test]
    fn condition_slice_last_distinct_kind_returns_none_on_empty_slice() {
        let empty: &[Condition] = &[];
        assert_eq!(
            empty.last_distinct_kind(),
            None,
            "empty slice must return None on last_distinct_kind",
        );
        assert_eq!(
            empty.last_distinct_kind(),
            empty.distinct_kinds().last().copied(),
            "empty last_distinct_kind must equal distinct_kinds().last().copied()",
        );
    }

    /// PER-VARIANT pin — a slice with EXACTLY ONE `Condition` carrying
    /// the addressed kind returns `Some(that_kind)` on
    /// `last_distinct_kind` (single hit; earliest = latest endpoint).
    #[test]
    fn condition_slice_last_distinct_kind_returns_populated_variant() {
        for populated in ConditionKind::ALL {
            let slice = [condition_with(populated)];
            assert_eq!(
                slice.last_distinct_kind(),
                Some(populated),
                "single-populated slice must return Some({populated:?}) on last_distinct_kind",
            );
            assert_eq!(
                slice.last_distinct_kind(),
                slice.distinct_kinds().last().copied(),
                "single-populated last_distinct_kind must equal distinct_kinds().last().copied() for {populated:?}",
            );
            // On single-populated slice both endpoint projections agree.
            assert_eq!(
                slice.last_distinct_kind(),
                slice.first_distinct_kind(),
                "single-populated last_distinct_kind must equal first_distinct_kind for {populated:?} (single hit ⇒ earliest = latest)",
            );
        }
    }

    /// FULL-COVERAGE pin — a slice that carries every [`ConditionKind`]
    /// variant returns `Some(*ConditionKind::ALL.last().unwrap())` on
    /// `last_distinct_kind` (the last ALL entry hits at the earliest
    /// walk step of the REVERSED walk).
    #[test]
    fn condition_slice_last_distinct_kind_returns_last_all_on_saturated_slice() {
        let saturated: Vec<Condition> =
            ConditionKind::ALL.into_iter().map(condition_with).collect();
        let last_all = ConditionKind::ALL.last().copied();
        assert_eq!(
            saturated.as_slice().last_distinct_kind(),
            last_all,
            "saturated slice must return Some(*ConditionKind::ALL.last().unwrap()) on last_distinct_kind",
        );
        assert_eq!(
            saturated.as_slice().last_distinct_kind(),
            saturated.as_slice().distinct_kinds().last().copied(),
            "saturated last_distinct_kind must equal distinct_kinds().last().copied()",
        );
    }

    // ── ConditionSliceExt::last_missing_kind — latest-element pins ─────

    /// EMPTY-SLICE pin — an empty slice returns
    /// `Some(*ConditionKind::ALL.last().unwrap())` on `last_missing_kind`
    /// (every kind missing, latest hit is the last ALL entry). Dual of
    /// the empty-slice arm on `last_distinct_kind` which returns `None`.
    #[test]
    fn condition_slice_last_missing_kind_returns_last_all_on_empty_slice() {
        let empty: &[Condition] = &[];
        let last_all = ConditionKind::ALL.last().copied();
        assert_eq!(
            empty.last_missing_kind(),
            last_all,
            "empty slice must return Some(*ConditionKind::ALL.last().unwrap()) on last_missing_kind",
        );
        assert_eq!(
            empty.last_missing_kind(),
            empty.missing_kinds().last().copied(),
            "empty last_missing_kind must equal missing_kinds().last().copied()",
        );
    }

    /// PER-VARIANT pin — a slice populating exactly `k` returns
    /// `Some(*ALL.last().unwrap())` if `k != ALL.last().unwrap()`, else
    /// `Some(ALL[ALL.len() - 2])` (the latest ALL entry != `k`).
    #[test]
    fn condition_slice_last_missing_kind_returns_latest_absent_variant() {
        for populated in ConditionKind::ALL {
            let slice = [condition_with(populated)];
            let expected = ConditionKind::ALL
                .into_iter()
                .rev()
                .find(|k| *k != populated);
            assert_eq!(
                slice.last_missing_kind(),
                expected,
                "single-populated slice must return latest ALL entry != {populated:?} on last_missing_kind",
            );
            assert_eq!(
                slice.last_missing_kind(),
                slice.missing_kinds().last().copied(),
                "single-populated last_missing_kind must equal missing_kinds().last().copied() for {populated:?}",
            );
        }
    }

    /// FULL-COVERAGE pin — a slice that carries every [`ConditionKind`]
    /// variant returns `None` on `last_missing_kind` (no kind missing).
    #[test]
    fn condition_slice_last_missing_kind_returns_none_on_saturated_slice() {
        let saturated: Vec<Condition> =
            ConditionKind::ALL.into_iter().map(condition_with).collect();
        assert_eq!(
            saturated.as_slice().last_missing_kind(),
            None,
            "saturated slice must return None on last_missing_kind",
        );
        assert_eq!(
            saturated.as_slice().last_missing_kind(),
            saturated.as_slice().missing_kinds().last().copied(),
            "saturated last_missing_kind must equal missing_kinds().last().copied()",
        );
    }

    // ── Boundary distinct-set triad — substrate-delegation pins ────────
    //
    // The (precondition, postcondition, condition-union) distinct-set
    // triad on [`Boundary`] delegates to the slice-level substrate
    // primitive [`ConditionSliceExt::distinct_kinds`] on each half-slice
    // and composes the union via [`Self::has_condition_kind`] over
    // [`ConditionKind::ALL`]. The dedicated tests below pin each arm's
    // delegation shape; the substrate testkit macro
    // `assert_surface_union_composition_laws` (extended in this commit
    // with the closed-set-inversion arm) pins the union composition law
    // against the two half-slice arms in canonical ALL-order.

    /// SUBSTRATE-DELEGATION pin (Boundary distinct-kind-count triad)
    /// — the three `distinct_*_kind_count` methods on [`Boundary`]
    /// delegate to the slice-level substrate primitive
    /// [`ConditionSliceExt::distinct_kind_count`] over the two
    /// `Vec<Condition>` slots (precondition + postcondition) and
    /// compose the union scalar via
    /// `ConditionKind::ALL.filter(|k| has_condition_kind(*k)).count()`.
    /// Sweep `ConditionKind::ALL × ConditionKind::ALL` so a regression
    /// that (a) inlined a divergent closed-set walk at either half-slice
    /// arm, (b) reversed the union walk order, or (c) narrowed the
    /// union to an intersection surfaces HERE. Also pins the
    /// composition law
    /// `distinct_*_kind_count() == distinct_*_kinds().len()` at each
    /// arm — a regression that overrode the scalar projection to skip a
    /// kind or double-count a slot fails HERE.
    #[test]
    fn distinct_condition_kind_count_triad_delegates_and_matches_distinct_kinds_len() {
        // Empty boundary — every arm returns 0.
        let b = Boundary::default();
        for kind in ConditionKind::ALL {
            assert_eq!(
                b.distinct_precondition_kind_count(),
                0,
                "empty boundary must return 0 on distinct_precondition_kind_count, kind={kind:?}",
            );
            assert_eq!(
                b.distinct_postcondition_kind_count(),
                0,
                "empty boundary must return 0 on distinct_postcondition_kind_count, kind={kind:?}",
            );
            assert_eq!(
                b.distinct_condition_kind_count(),
                0,
                "empty boundary must return 0 on distinct_condition_kind_count, kind={kind:?}",
            );
        }

        for pre_kind in ConditionKind::ALL {
            for post_kind in ConditionKind::ALL {
                let mut b = Boundary::default();
                b.preconditions.push(condition_with(pre_kind));
                b.postconditions.push(condition_with(post_kind));

                assert_eq!(
                    b.distinct_precondition_kind_count(),
                    b.preconditions.distinct_kind_count(),
                    "Boundary::distinct_precondition_kind_count must delegate verbatim to \
                     preconditions.distinct_kind_count() for pre={pre_kind:?} post={post_kind:?}",
                );
                assert_eq!(
                    b.distinct_precondition_kind_count(),
                    b.distinct_precondition_kinds().len(),
                    "Boundary::distinct_precondition_kind_count must equal \
                     distinct_precondition_kinds().len() for pre={pre_kind:?} post={post_kind:?}",
                );
                assert_eq!(
                    b.distinct_postcondition_kind_count(),
                    b.postconditions.distinct_kind_count(),
                    "Boundary::distinct_postcondition_kind_count must delegate verbatim to \
                     postconditions.distinct_kind_count() for pre={pre_kind:?} post={post_kind:?}",
                );
                assert_eq!(
                    b.distinct_postcondition_kind_count(),
                    b.distinct_postcondition_kinds().len(),
                    "Boundary::distinct_postcondition_kind_count must equal \
                     distinct_postcondition_kinds().len() for pre={pre_kind:?} post={post_kind:?}",
                );
                let expected_union_count = if pre_kind == post_kind { 1 } else { 2 };
                assert_eq!(
                    b.distinct_condition_kind_count(),
                    expected_union_count,
                    "Boundary::distinct_condition_kind_count must count distinct union kinds \
                     for pre={pre_kind:?} post={post_kind:?}",
                );
                assert_eq!(
                    b.distinct_condition_kind_count(),
                    b.distinct_condition_kinds().len(),
                    "Boundary::distinct_condition_kind_count must equal \
                     distinct_condition_kinds().len() for pre={pre_kind:?} post={post_kind:?}",
                );
            }
        }
    }

    /// SUBSTRATE-DELEGATION pin (Boundary distinct-set triad) — the
    /// three `distinct_*_kinds` methods on [`Boundary`] delegate to the
    /// slice-level substrate primitive over the two `Vec<Condition>`
    /// slots (precondition + postcondition) and compose the union via
    /// `ConditionKind::ALL.filter(|k| has_condition_kind(*k))`. Sweep
    /// `ConditionKind::ALL × ConditionKind::ALL` so a regression that
    /// (a) inlined a divergent closed-set walk at either half-slice
    /// arm, (b) reversed the union walk order, or (c) narrowed the
    /// union to an intersection surfaces HERE.
    #[test]
    fn distinct_condition_kinds_triad_delegates_to_slice_distinct_kinds() {
        for pre_kind in ConditionKind::ALL {
            for post_kind in ConditionKind::ALL {
                let mut b = Boundary::default();
                b.preconditions.push(condition_with(pre_kind));
                b.postconditions.push(condition_with(post_kind));

                assert_eq!(
                    b.distinct_precondition_kinds(),
                    b.preconditions.distinct_kinds(),
                    "Boundary::distinct_precondition_kinds must delegate verbatim to \
                     preconditions.distinct_kinds() for pre={pre_kind:?} post={post_kind:?}",
                );
                assert_eq!(
                    b.distinct_postcondition_kinds(),
                    b.postconditions.distinct_kinds(),
                    "Boundary::distinct_postcondition_kinds must delegate verbatim to \
                     postconditions.distinct_kinds() for pre={pre_kind:?} post={post_kind:?}",
                );
                let expected_union: Vec<_> = ConditionKind::ALL
                    .into_iter()
                    .filter(|k| pre_kind == *k || post_kind == *k)
                    .collect();
                assert_eq!(
                    b.distinct_condition_kinds(),
                    expected_union,
                    "Boundary::distinct_condition_kinds must equal ConditionKind::ALL-ordered \
                     set-union of the two half-slice distinct-sets for pre={pre_kind:?} post={post_kind:?}",
                );
            }
        }
    }

    /// SUBSTRATE-DELEGATION pin (Boundary distinct-set ITERATOR triad) —
    /// the three `iter_distinct_*_condition_kinds` methods on [`Boundary`]
    /// delegate to the slice-level substrate primitive
    /// [`ConditionSliceExt::iter_distinct_kinds`] over the two
    /// `Vec<Condition>` slots (precondition + postcondition) and compose
    /// the union via `ConditionKind::ALL.iter().copied().filter(|&k|
    /// has_condition_kind(k))`. Byte-for-byte peer of
    /// [`distinct_condition_kinds_triad_delegates_to_slice_distinct_kinds`]
    /// on the iterator side — the two tests share ONE closed-set walk
    /// semantics and pin the composition law
    /// `iter_distinct_*_condition_kinds().collect::<Vec<_>>() ==
    /// distinct_*_condition_kinds()` for every arm across
    /// `ConditionKind::ALL × ConditionKind::ALL`. A regression that
    /// materialized the Vec then re-iterated it (round-trip through the
    /// heap), drifted the yield order, or diverged from the widened
    /// primitive on any arm surfaces HERE.
    #[test]
    fn iter_distinct_condition_kinds_triad_delegates_to_slice_iter_distinct_kinds() {
        for pre_kind in ConditionKind::ALL {
            for post_kind in ConditionKind::ALL {
                let mut b = Boundary::default();
                b.preconditions.push(condition_with(pre_kind));
                b.postconditions.push(condition_with(post_kind));

                let pre_via_iter: Vec<_> = b.iter_distinct_precondition_kinds().collect();
                let pre_via_vec = b.distinct_precondition_kinds();
                assert_eq!(
                    pre_via_iter, pre_via_vec,
                    "Boundary::iter_distinct_precondition_kinds().collect() drifted from \
                     distinct_precondition_kinds() for pre={pre_kind:?} post={post_kind:?}",
                );
                let post_via_iter: Vec<_> = b.iter_distinct_postcondition_kinds().collect();
                let post_via_vec = b.distinct_postcondition_kinds();
                assert_eq!(
                    post_via_iter, post_via_vec,
                    "Boundary::iter_distinct_postcondition_kinds().collect() drifted from \
                     distinct_postcondition_kinds() for pre={pre_kind:?} post={post_kind:?}",
                );
                let union_via_iter: Vec<_> = b.iter_distinct_condition_kinds().collect();
                let union_via_vec = b.distinct_condition_kinds();
                assert_eq!(
                    union_via_iter, union_via_vec,
                    "Boundary::iter_distinct_condition_kinds().collect() drifted from \
                     distinct_condition_kinds() for pre={pre_kind:?} post={post_kind:?}",
                );
            }
        }
    }

    /// SUBSTRATE-DELEGATION pin (Boundary missing-set ITERATOR triad) —
    /// the three `iter_missing_*_condition_kinds` methods on [`Boundary`]
    /// delegate to the slice-level substrate primitive
    /// [`ConditionSliceExt::iter_missing_kinds`] over the two
    /// `Vec<Condition>` slots (precondition + postcondition) and compose
    /// the union via `ConditionKind::ALL.iter().copied().filter(|&k|
    /// !has_condition_kind(k))`. Peer of
    /// [`iter_distinct_condition_kinds_triad_delegates_to_slice_iter_distinct_kinds`]
    /// on the missing side under a NEGATED point-probe.
    #[test]
    fn iter_missing_condition_kinds_triad_delegates_to_slice_iter_missing_kinds() {
        // Empty boundary — every iter arm yields ConditionKind::ALL.
        let b = Boundary::default();
        let all: Vec<_> = ConditionKind::ALL.to_vec();
        assert_eq!(
            b.iter_missing_precondition_kinds().collect::<Vec<_>>(),
            all,
            "empty boundary must yield ConditionKind::ALL on iter_missing_precondition_kinds",
        );
        assert_eq!(
            b.iter_missing_postcondition_kinds().collect::<Vec<_>>(),
            all,
            "empty boundary must yield ConditionKind::ALL on iter_missing_postcondition_kinds",
        );
        assert_eq!(
            b.iter_missing_condition_kinds().collect::<Vec<_>>(),
            all,
            "empty boundary must yield ConditionKind::ALL on iter_missing_condition_kinds",
        );

        for pre_kind in ConditionKind::ALL {
            for post_kind in ConditionKind::ALL {
                let mut b = Boundary::default();
                b.preconditions.push(condition_with(pre_kind));
                b.postconditions.push(condition_with(post_kind));

                let pre_via_iter: Vec<_> = b.iter_missing_precondition_kinds().collect();
                let pre_via_vec = b.missing_precondition_kinds();
                assert_eq!(
                    pre_via_iter, pre_via_vec,
                    "Boundary::iter_missing_precondition_kinds().collect() drifted from \
                     missing_precondition_kinds() for pre={pre_kind:?} post={post_kind:?}",
                );
                let post_via_iter: Vec<_> = b.iter_missing_postcondition_kinds().collect();
                let post_via_vec = b.missing_postcondition_kinds();
                assert_eq!(
                    post_via_iter, post_via_vec,
                    "Boundary::iter_missing_postcondition_kinds().collect() drifted from \
                     missing_postcondition_kinds() for pre={pre_kind:?} post={post_kind:?}",
                );
                let union_via_iter: Vec<_> = b.iter_missing_condition_kinds().collect();
                let union_via_vec = b.missing_condition_kinds();
                assert_eq!(
                    union_via_iter, union_via_vec,
                    "Boundary::iter_missing_condition_kinds().collect() drifted from \
                     missing_condition_kinds() for pre={pre_kind:?} post={post_kind:?}",
                );
            }
        }
    }

    /// SUBSTRATE-DELEGATION pin (Boundary missing-set triad) — the
    /// three `missing_*_kinds` methods on [`Boundary`] delegate to the
    /// slice-level substrate primitive
    /// [`ConditionSliceExt::missing_kinds`] over the two
    /// `Vec<Condition>` slots (precondition + postcondition) and
    /// compose the union via
    /// `ConditionKind::ALL.filter(|k| !has_condition_kind(*k))`. Sweep
    /// `ConditionKind::ALL × ConditionKind::ALL` so a regression that
    /// (a) inlined a divergent closed-set walk at either half-slice
    /// arm, (b) reversed the union walk order, (c) widened the union
    /// intersection to a union (a `||` inlined where `&&` is required
    /// on the missing side), or (d) forgot the negation surfaces HERE.
    /// Also pins the empty-boundary edge case: every arm returns
    /// `ConditionKind::ALL.to_vec()` on an empty boundary.
    #[test]
    fn missing_condition_kinds_triad_delegates_to_slice_missing_kinds() {
        // Empty boundary — every arm returns ConditionKind::ALL (nothing
        // is populated, so every kind is missing on all three slots).
        let b = Boundary::default();
        let all_kinds = ConditionKind::ALL.to_vec();
        assert_eq!(
            b.missing_precondition_kinds(),
            all_kinds,
            "empty boundary must return ConditionKind::ALL on missing_precondition_kinds",
        );
        assert_eq!(
            b.missing_postcondition_kinds(),
            all_kinds,
            "empty boundary must return ConditionKind::ALL on missing_postcondition_kinds",
        );
        assert_eq!(
            b.missing_condition_kinds(),
            all_kinds,
            "empty boundary must return ConditionKind::ALL on missing_condition_kinds",
        );

        for pre_kind in ConditionKind::ALL {
            for post_kind in ConditionKind::ALL {
                let mut b = Boundary::default();
                b.preconditions.push(condition_with(pre_kind));
                b.postconditions.push(condition_with(post_kind));

                assert_eq!(
                    b.missing_precondition_kinds(),
                    b.preconditions.missing_kinds(),
                    "Boundary::missing_precondition_kinds must delegate verbatim to \
                     preconditions.missing_kinds() for pre={pre_kind:?} post={post_kind:?}",
                );
                assert_eq!(
                    b.missing_postcondition_kinds(),
                    b.postconditions.missing_kinds(),
                    "Boundary::missing_postcondition_kinds must delegate verbatim to \
                     postconditions.missing_kinds() for pre={pre_kind:?} post={post_kind:?}",
                );
                // Union: a kind is missing from the union iff it is
                // missing from BOTH half-slices (SET-INTERSECTION).
                let expected_union: Vec<_> = ConditionKind::ALL
                    .into_iter()
                    .filter(|k| pre_kind != *k && post_kind != *k)
                    .collect();
                assert_eq!(
                    b.missing_condition_kinds(),
                    expected_union,
                    "Boundary::missing_condition_kinds must equal ConditionKind::ALL-ordered \
                     set-INTERSECTION of the two half-slice missing-sets for pre={pre_kind:?} post={post_kind:?}",
                );
                // Partition invariant: distinct ∪ missing == ALL, disjoint.
                let distinct = b.distinct_condition_kinds();
                let missing = b.missing_condition_kinds();
                for kind in ConditionKind::ALL {
                    assert!(
                        distinct.contains(&kind) ^ missing.contains(&kind),
                        "(distinct, missing) partition violated on {kind:?} for pre={pre_kind:?} post={post_kind:?}",
                    );
                }
                assert_eq!(
                    distinct.len() + missing.len(),
                    ConditionKind::ALL.len(),
                    "Boundary (distinct, missing) cardinality partition drift for pre={pre_kind:?} post={post_kind:?}",
                );
            }
        }
    }

    /// SUBSTRATE-DELEGATION pin (Boundary missing-kind-count triad) —
    /// the three `missing_*_kind_count` methods on [`Boundary`] delegate
    /// to the slice-level substrate primitive
    /// [`ConditionSliceExt::missing_kind_count`] over the two
    /// `Vec<Condition>` slots (precondition + postcondition) and
    /// compose the union via
    /// `ConditionKind::ALL.iter().filter(|k|
    /// !self.has_condition_kind(**k)).count()`. Sweep
    /// `ConditionKind::ALL × ConditionKind::ALL` so a regression that
    /// (a) inlined a divergent negated closed-set walk at either half-
    /// slice arm, (b) dropped the negation on the union arm, or (c)
    /// drifted from the widened-primitive length surfaces HERE. Also
    /// pins the scalar-partition invariant
    /// `distinct_kind_count + missing_kind_count == ConditionKind::ALL.len()`
    /// per arrangement.
    #[test]
    fn missing_condition_kind_count_triad_delegates_to_slice_missing_kind_count() {
        // Empty boundary — every arm returns ConditionKind::ALL.len()
        // (nothing is populated, so every kind is missing on all three
        // slots).
        let b = Boundary::default();
        let total = ConditionKind::ALL.len();
        assert_eq!(
            b.missing_precondition_kind_count(),
            total,
            "empty boundary must return ConditionKind::ALL.len() on missing_precondition_kind_count",
        );
        assert_eq!(
            b.missing_postcondition_kind_count(),
            total,
            "empty boundary must return ConditionKind::ALL.len() on missing_postcondition_kind_count",
        );
        assert_eq!(
            b.missing_condition_kind_count(),
            total,
            "empty boundary must return ConditionKind::ALL.len() on missing_condition_kind_count",
        );

        for pre_kind in ConditionKind::ALL {
            for post_kind in ConditionKind::ALL {
                let mut b = Boundary::default();
                b.preconditions.push(condition_with(pre_kind));
                b.postconditions.push(condition_with(post_kind));

                // Half-slice arms delegate byte-for-byte to the slice
                // substrate primitive.
                assert_eq!(
                    b.missing_precondition_kind_count(),
                    b.preconditions.missing_kind_count(),
                    "Boundary::missing_precondition_kind_count must delegate verbatim to \
                     preconditions.missing_kind_count() for pre={pre_kind:?} post={post_kind:?}",
                );
                assert_eq!(
                    b.missing_postcondition_kind_count(),
                    b.postconditions.missing_kind_count(),
                    "Boundary::missing_postcondition_kind_count must delegate verbatim to \
                     postconditions.missing_kind_count() for pre={pre_kind:?} post={post_kind:?}",
                );
                // Union arm equals missing_condition_kinds().len() — the
                // scalar cardinality of the two-slice intersection.
                assert_eq!(
                    b.missing_condition_kind_count(),
                    b.missing_condition_kinds().len(),
                    "Boundary::missing_condition_kind_count must equal missing_condition_kinds().len() \
                     for pre={pre_kind:?} post={post_kind:?}",
                );
                // Scalar-partition invariant: distinct + missing == ALL.
                assert_eq!(
                    b.distinct_condition_kind_count() + b.missing_condition_kind_count(),
                    ConditionKind::ALL.len(),
                    "Boundary (distinct, missing) scalar partition drift for pre={pre_kind:?} post={post_kind:?}",
                );
            }
        }
    }

    /// SUBSTRATE-DELEGATION pin (Boundary first-distinct-kind triad) —
    /// the three `first_distinct_*_kind` methods on [`Boundary`]
    /// delegate to the slice-level substrate primitive
    /// [`ConditionSliceExt::first_distinct_kind`] over the two
    /// `Vec<Condition>` slots (precondition + postcondition) and
    /// compose the union via `ConditionKind::ALL.iter().copied()
    /// .find(|k| has_condition_kind(*k))`. Sweep
    /// `ConditionKind::ALL × ConditionKind::ALL` so a regression that
    /// inlined a divergent short-circuit walk at either half-slice arm,
    /// reversed the walk order, or dropped the short-circuit surfaces
    /// HERE. Also pins the composition law `first_distinct_*_kind() ==
    /// distinct_*_kinds().first().copied()` at each arm.
    #[test]
    fn first_distinct_condition_kind_triad_delegates_to_slice_first_distinct_kind() {
        // Empty boundary — every arm returns None.
        let b = Boundary::default();
        assert_eq!(
            b.first_distinct_precondition_kind(),
            None,
            "empty boundary must return None on first_distinct_precondition_kind",
        );
        assert_eq!(
            b.first_distinct_postcondition_kind(),
            None,
            "empty boundary must return None on first_distinct_postcondition_kind",
        );
        assert_eq!(
            b.first_distinct_condition_kind(),
            None,
            "empty boundary must return None on first_distinct_condition_kind",
        );

        for pre_kind in ConditionKind::ALL {
            for post_kind in ConditionKind::ALL {
                let mut b = Boundary::default();
                b.preconditions.push(condition_with(pre_kind));
                b.postconditions.push(condition_with(post_kind));

                assert_eq!(
                    b.first_distinct_precondition_kind(),
                    b.preconditions.first_distinct_kind(),
                    "Boundary::first_distinct_precondition_kind must delegate verbatim to \
                     preconditions.first_distinct_kind() for pre={pre_kind:?} post={post_kind:?}",
                );
                assert_eq!(
                    b.first_distinct_precondition_kind(),
                    b.distinct_precondition_kinds().first().copied(),
                    "Boundary::first_distinct_precondition_kind must equal \
                     distinct_precondition_kinds().first().copied() for pre={pre_kind:?} post={post_kind:?}",
                );
                assert_eq!(
                    b.first_distinct_postcondition_kind(),
                    b.postconditions.first_distinct_kind(),
                    "Boundary::first_distinct_postcondition_kind must delegate verbatim to \
                     postconditions.first_distinct_kind() for pre={pre_kind:?} post={post_kind:?}",
                );
                assert_eq!(
                    b.first_distinct_postcondition_kind(),
                    b.distinct_postcondition_kinds().first().copied(),
                    "Boundary::first_distinct_postcondition_kind must equal \
                     distinct_postcondition_kinds().first().copied() for pre={pre_kind:?} post={post_kind:?}",
                );
                let expected_union = ConditionKind::ALL
                    .into_iter()
                    .find(|k| pre_kind == *k || post_kind == *k);
                assert_eq!(
                    b.first_distinct_condition_kind(),
                    expected_union,
                    "Boundary::first_distinct_condition_kind must equal earliest ALL entry \
                     populated by either half-slice for pre={pre_kind:?} post={post_kind:?}",
                );
                assert_eq!(
                    b.first_distinct_condition_kind(),
                    b.distinct_condition_kinds().first().copied(),
                    "Boundary::first_distinct_condition_kind must equal \
                     distinct_condition_kinds().first().copied() for pre={pre_kind:?} post={post_kind:?}",
                );
            }
        }
    }

    /// SUBSTRATE-DELEGATION pin (Boundary first-missing-kind triad) —
    /// the three `first_missing_*_kind` methods on [`Boundary`]
    /// delegate to the slice-level substrate primitive
    /// [`ConditionSliceExt::first_missing_kind`] over the two
    /// `Vec<Condition>` slots (precondition + postcondition) and
    /// compose the union via `ConditionKind::ALL.iter().copied()
    /// .find(|k| !has_condition_kind(*k))`. Sweep
    /// `ConditionKind::ALL × ConditionKind::ALL` so a regression that
    /// dropped the negation or drifted the short-circuit walk surfaces
    /// HERE. Also pins the composition law `first_missing_*_kind() ==
    /// missing_*_kinds().first().copied()` at each arm.
    #[test]
    fn first_missing_condition_kind_triad_delegates_to_slice_first_missing_kind() {
        // Empty boundary — every arm returns Some(ConditionKind::ALL[0]).
        let b = Boundary::default();
        let first = Some(ConditionKind::ALL[0]);
        assert_eq!(
            b.first_missing_precondition_kind(),
            first,
            "empty boundary must return Some(ConditionKind::ALL[0]) on first_missing_precondition_kind",
        );
        assert_eq!(
            b.first_missing_postcondition_kind(),
            first,
            "empty boundary must return Some(ConditionKind::ALL[0]) on first_missing_postcondition_kind",
        );
        assert_eq!(
            b.first_missing_condition_kind(),
            first,
            "empty boundary must return Some(ConditionKind::ALL[0]) on first_missing_condition_kind",
        );

        for pre_kind in ConditionKind::ALL {
            for post_kind in ConditionKind::ALL {
                let mut b = Boundary::default();
                b.preconditions.push(condition_with(pre_kind));
                b.postconditions.push(condition_with(post_kind));

                assert_eq!(
                    b.first_missing_precondition_kind(),
                    b.preconditions.first_missing_kind(),
                    "Boundary::first_missing_precondition_kind must delegate verbatim to \
                     preconditions.first_missing_kind() for pre={pre_kind:?} post={post_kind:?}",
                );
                assert_eq!(
                    b.first_missing_precondition_kind(),
                    b.missing_precondition_kinds().first().copied(),
                    "Boundary::first_missing_precondition_kind must equal \
                     missing_precondition_kinds().first().copied() for pre={pre_kind:?} post={post_kind:?}",
                );
                assert_eq!(
                    b.first_missing_postcondition_kind(),
                    b.postconditions.first_missing_kind(),
                    "Boundary::first_missing_postcondition_kind must delegate verbatim to \
                     postconditions.first_missing_kind() for pre={pre_kind:?} post={post_kind:?}",
                );
                assert_eq!(
                    b.first_missing_postcondition_kind(),
                    b.missing_postcondition_kinds().first().copied(),
                    "Boundary::first_missing_postcondition_kind must equal \
                     missing_postcondition_kinds().first().copied() for pre={pre_kind:?} post={post_kind:?}",
                );
                let expected_union = ConditionKind::ALL
                    .into_iter()
                    .find(|k| pre_kind != *k && post_kind != *k);
                assert_eq!(
                    b.first_missing_condition_kind(),
                    expected_union,
                    "Boundary::first_missing_condition_kind must equal earliest ALL entry \
                     NOT populated by either half-slice for pre={pre_kind:?} post={post_kind:?}",
                );
                assert_eq!(
                    b.first_missing_condition_kind(),
                    b.missing_condition_kinds().first().copied(),
                    "Boundary::first_missing_condition_kind must equal \
                     missing_condition_kinds().first().copied() for pre={pre_kind:?} post={post_kind:?}",
                );
            }
        }
    }

    /// SUBSTRATE-DELEGATION pin (Boundary last-distinct-kind triad)
    /// — the three `last_distinct_*_kind` methods on [`Boundary`]
    /// delegate to the slice-level substrate primitive
    /// [`ConditionSliceExt::last_distinct_kind`] over the two
    /// `Vec<Condition>` slots (precondition + postcondition) and
    /// compose the union via `ConditionKind::ALL.iter().rev().copied()
    /// .find(|k| has_condition_kind(*k))`. Sweep
    /// `ConditionKind::ALL × ConditionKind::ALL` so a regression that
    /// (a) forgot to reverse the walk (returning `first_distinct_*_kind`),
    /// (b) inlined a divergent closed-set walk at either half-slice
    /// arm, or (c) narrowed the union to an intersection surfaces
    /// HERE. Also pins the composition law `last_distinct_*_kind() ==
    /// distinct_*_kinds().last().copied()` at each arm.
    #[test]
    fn last_distinct_condition_kind_triad_delegates_to_slice_last_distinct_kind() {
        // Empty boundary — every arm returns None.
        let b = Boundary::default();
        assert_eq!(
            b.last_distinct_precondition_kind(),
            None,
            "empty boundary must return None on last_distinct_precondition_kind",
        );
        assert_eq!(
            b.last_distinct_postcondition_kind(),
            None,
            "empty boundary must return None on last_distinct_postcondition_kind",
        );
        assert_eq!(
            b.last_distinct_condition_kind(),
            None,
            "empty boundary must return None on last_distinct_condition_kind",
        );

        for pre_kind in ConditionKind::ALL {
            for post_kind in ConditionKind::ALL {
                let mut b = Boundary::default();
                b.preconditions.push(condition_with(pre_kind));
                b.postconditions.push(condition_with(post_kind));

                assert_eq!(
                    b.last_distinct_precondition_kind(),
                    b.preconditions.last_distinct_kind(),
                    "Boundary::last_distinct_precondition_kind must delegate verbatim to \
                     preconditions.last_distinct_kind() for pre={pre_kind:?} post={post_kind:?}",
                );
                assert_eq!(
                    b.last_distinct_precondition_kind(),
                    b.distinct_precondition_kinds().last().copied(),
                    "Boundary::last_distinct_precondition_kind must equal \
                     distinct_precondition_kinds().last().copied() for pre={pre_kind:?} post={post_kind:?}",
                );
                assert_eq!(
                    b.last_distinct_postcondition_kind(),
                    b.postconditions.last_distinct_kind(),
                    "Boundary::last_distinct_postcondition_kind must delegate verbatim to \
                     postconditions.last_distinct_kind() for pre={pre_kind:?} post={post_kind:?}",
                );
                assert_eq!(
                    b.last_distinct_postcondition_kind(),
                    b.distinct_postcondition_kinds().last().copied(),
                    "Boundary::last_distinct_postcondition_kind must equal \
                     distinct_postcondition_kinds().last().copied() for pre={pre_kind:?} post={post_kind:?}",
                );
                let expected_union = ConditionKind::ALL
                    .into_iter()
                    .rev()
                    .find(|k| pre_kind == *k || post_kind == *k);
                assert_eq!(
                    b.last_distinct_condition_kind(),
                    expected_union,
                    "Boundary::last_distinct_condition_kind must equal latest ALL entry \
                     populated by either half-slice for pre={pre_kind:?} post={post_kind:?}",
                );
                assert_eq!(
                    b.last_distinct_condition_kind(),
                    b.distinct_condition_kinds().last().copied(),
                    "Boundary::last_distinct_condition_kind must equal \
                     distinct_condition_kinds().last().copied() for pre={pre_kind:?} post={post_kind:?}",
                );
            }
        }
    }

    /// SUBSTRATE-DELEGATION pin (Boundary last-missing-kind triad) —
    /// the three `last_missing_*_kind` methods on [`Boundary`]
    /// delegate to the slice-level substrate primitive
    /// [`ConditionSliceExt::last_missing_kind`] over the two
    /// `Vec<Condition>` slots (precondition + postcondition) and
    /// compose the union via `ConditionKind::ALL.iter().rev().copied()
    /// .find(|k| !has_condition_kind(*k))`. Sweep
    /// `ConditionKind::ALL × ConditionKind::ALL` so a regression that
    /// dropped the negation or forgot the reversed short-circuit walk
    /// surfaces HERE. Also pins the composition law `last_missing_*_kind()
    /// == missing_*_kinds().last().copied()` at each arm.
    #[test]
    fn last_missing_condition_kind_triad_delegates_to_slice_last_missing_kind() {
        // Empty boundary — every arm returns Some(*ConditionKind::ALL.last().unwrap()).
        let b = Boundary::default();
        let last = ConditionKind::ALL.last().copied();
        assert_eq!(
            b.last_missing_precondition_kind(),
            last,
            "empty boundary must return Some(*ConditionKind::ALL.last().unwrap()) on last_missing_precondition_kind",
        );
        assert_eq!(
            b.last_missing_postcondition_kind(),
            last,
            "empty boundary must return Some(*ConditionKind::ALL.last().unwrap()) on last_missing_postcondition_kind",
        );
        assert_eq!(
            b.last_missing_condition_kind(),
            last,
            "empty boundary must return Some(*ConditionKind::ALL.last().unwrap()) on last_missing_condition_kind",
        );

        for pre_kind in ConditionKind::ALL {
            for post_kind in ConditionKind::ALL {
                let mut b = Boundary::default();
                b.preconditions.push(condition_with(pre_kind));
                b.postconditions.push(condition_with(post_kind));

                assert_eq!(
                    b.last_missing_precondition_kind(),
                    b.preconditions.last_missing_kind(),
                    "Boundary::last_missing_precondition_kind must delegate verbatim to \
                     preconditions.last_missing_kind() for pre={pre_kind:?} post={post_kind:?}",
                );
                assert_eq!(
                    b.last_missing_precondition_kind(),
                    b.missing_precondition_kinds().last().copied(),
                    "Boundary::last_missing_precondition_kind must equal \
                     missing_precondition_kinds().last().copied() for pre={pre_kind:?} post={post_kind:?}",
                );
                assert_eq!(
                    b.last_missing_postcondition_kind(),
                    b.postconditions.last_missing_kind(),
                    "Boundary::last_missing_postcondition_kind must delegate verbatim to \
                     postconditions.last_missing_kind() for pre={pre_kind:?} post={post_kind:?}",
                );
                assert_eq!(
                    b.last_missing_postcondition_kind(),
                    b.missing_postcondition_kinds().last().copied(),
                    "Boundary::last_missing_postcondition_kind must equal \
                     missing_postcondition_kinds().last().copied() for pre={pre_kind:?} post={post_kind:?}",
                );
                let expected_union = ConditionKind::ALL
                    .into_iter()
                    .rev()
                    .find(|k| pre_kind != *k && post_kind != *k);
                assert_eq!(
                    b.last_missing_condition_kind(),
                    expected_union,
                    "Boundary::last_missing_condition_kind must equal latest ALL entry \
                     NOT populated by either half-slice for pre={pre_kind:?} post={post_kind:?}",
                );
                assert_eq!(
                    b.last_missing_condition_kind(),
                    b.missing_condition_kinds().last().copied(),
                    "Boundary::last_missing_condition_kind must equal \
                     missing_condition_kinds().last().copied() for pre={pre_kind:?} post={post_kind:?}",
                );
            }
        }
    }

    /// SUBSTRATE-DELEGATION pin (Boundary saturation-predicate triad)
    /// — the three `is_*_kind_saturated` methods on [`Boundary`]
    /// delegate to the slice-level substrate primitive
    /// [`ConditionSliceExt::is_kind_saturated`] over the two
    /// `Vec<Condition>` slots (precondition + postcondition) and
    /// compose the union via `ConditionKind::ALL.iter().all(|k|
    /// has_condition_kind(*k))`. Sweeps the empty boundary (every arm
    /// returns `false`), a single-populated-per-side arrangement (both
    /// per-slice arms return `false` on any `N ≥ 2` closed set; the
    /// union returns `false` unless the two kinds are distinct AND
    /// `N == 2`), and the saturated boundary (both slices carry every
    /// [`ConditionKind`], every arm returns `true`). Also pins the
    /// composition law `is_*_kind_saturated() ==
    /// missing_*_kinds().is_empty()` at each arm — a regression that
    /// dropped the `all` short-circuit, drifted the walk from
    /// `ConditionKind::ALL`, or negated the wrong side surfaces HERE.
    #[test]
    fn is_condition_kind_saturated_triad_delegates_to_slice_is_kind_saturated() {
        // Empty boundary — every arm returns false; missing_*_kinds
        // covers the full closed set on every arm.
        let b = Boundary::default();
        assert!(
            !b.is_precondition_kind_saturated(),
            "empty boundary must return false on is_precondition_kind_saturated",
        );
        assert!(
            !b.is_postcondition_kind_saturated(),
            "empty boundary must return false on is_postcondition_kind_saturated",
        );
        assert!(
            !b.is_condition_kind_saturated(),
            "empty boundary must return false on is_condition_kind_saturated",
        );
        assert_eq!(
            b.is_precondition_kind_saturated(),
            b.missing_precondition_kinds().is_empty(),
            "empty is_precondition_kind_saturated must equal missing_precondition_kinds().is_empty()",
        );

        // Single-populated per side — every per-slice arm returns
        // false on any N ≥ 2 closed set; the union returns false too
        // (needs every ALL kind covered).
        for pre_kind in ConditionKind::ALL {
            for post_kind in ConditionKind::ALL {
                let mut b = Boundary::default();
                b.preconditions.push(condition_with(pre_kind));
                b.postconditions.push(condition_with(post_kind));
                assert_eq!(
                    b.is_precondition_kind_saturated(),
                    b.preconditions.is_kind_saturated(),
                    "Boundary::is_precondition_kind_saturated must delegate verbatim to \
                     preconditions.is_kind_saturated() for pre={pre_kind:?} post={post_kind:?}",
                );
                assert_eq!(
                    b.is_postcondition_kind_saturated(),
                    b.postconditions.is_kind_saturated(),
                    "Boundary::is_postcondition_kind_saturated must delegate verbatim to \
                     postconditions.is_kind_saturated() for pre={pre_kind:?} post={post_kind:?}",
                );
                let expected_union = ConditionKind::ALL
                    .iter()
                    .all(|k| pre_kind == *k || post_kind == *k);
                assert_eq!(
                    b.is_condition_kind_saturated(),
                    expected_union,
                    "Boundary::is_condition_kind_saturated must equal all-ALL-covered-by-either-slice \
                     for pre={pre_kind:?} post={post_kind:?}",
                );
                assert_eq!(
                    b.is_condition_kind_saturated(),
                    b.missing_condition_kinds().is_empty(),
                    "Boundary::is_condition_kind_saturated must equal missing_condition_kinds().is_empty() \
                     for pre={pre_kind:?} post={post_kind:?}",
                );
            }
        }

        // Saturated boundary — both slices carry every ConditionKind
        // at least once, every arm returns true.
        let mut b = Boundary::default();
        for k in ConditionKind::ALL {
            b.preconditions.push(condition_with(k));
            b.postconditions.push(condition_with(k));
        }
        assert!(
            b.is_precondition_kind_saturated(),
            "saturated boundary must return true on is_precondition_kind_saturated",
        );
        assert!(
            b.is_postcondition_kind_saturated(),
            "saturated boundary must return true on is_postcondition_kind_saturated",
        );
        assert!(
            b.is_condition_kind_saturated(),
            "saturated boundary must return true on is_condition_kind_saturated",
        );
    }

    /// SUBSTRATE-DELEGATION pin (Boundary at-least-one halfspace
    /// triad) — the three `has_any_missing_*_condition_kind` methods
    /// on [`Boundary`] delegate to the slice-level substrate primitive
    /// [`ConditionSliceExt::has_any_missing_kind`] over the two
    /// `Vec<Condition>` slots (precondition + postcondition) and
    /// compose the union via `!self.is_condition_kind_saturated()`.
    /// Sweeps the empty boundary (every arm returns `true`), a single-
    /// populated-per-side arrangement (both per-slice arms return
    /// `true` on any `N ≥ 2` closed set; the union returns `true`
    /// unless the two kinds together cover every ALL variant), and
    /// the saturated boundary (both slices carry every
    /// [`ConditionKind`], every arm returns `false`). Also pins the
    /// composition law `has_any_missing_*_condition_kind() ==
    /// !is_*_condition_kind_saturated()` at each arm — a regression
    /// that dropped the negation, drifted the underlying saturation
    /// primitive, or negated the wrong side surfaces HERE.
    #[test]
    fn has_any_missing_condition_kind_triad_delegates_to_slice_has_any_missing_kind() {
        // Empty boundary — every arm returns true (every kind is
        // missing from every slice + from the union).
        let b = Boundary::default();
        assert!(
            b.has_any_missing_precondition_kind(),
            "empty boundary must return true on has_any_missing_precondition_kind",
        );
        assert!(
            b.has_any_missing_postcondition_kind(),
            "empty boundary must return true on has_any_missing_postcondition_kind",
        );
        assert!(
            b.has_any_missing_condition_kind(),
            "empty boundary must return true on has_any_missing_condition_kind",
        );
        assert_eq!(
            b.has_any_missing_condition_kind(),
            !b.is_condition_kind_saturated(),
            "empty has_any_missing_condition_kind must equal !is_condition_kind_saturated()",
        );

        // Single-populated per side — sweep ALL × ALL. Every per-slice
        // arm returns true on any N ≥ 2 closed set; the union returns
        // true unless the two kinds together cover every ALL variant.
        for pre_kind in ConditionKind::ALL {
            for post_kind in ConditionKind::ALL {
                let mut b = Boundary::default();
                b.preconditions.push(condition_with(pre_kind));
                b.postconditions.push(condition_with(post_kind));
                assert_eq!(
                    b.has_any_missing_precondition_kind(),
                    b.preconditions.has_any_missing_kind(),
                    "Boundary::has_any_missing_precondition_kind must delegate verbatim to \
                     preconditions.has_any_missing_kind() for pre={pre_kind:?} post={post_kind:?}",
                );
                assert_eq!(
                    b.has_any_missing_postcondition_kind(),
                    b.postconditions.has_any_missing_kind(),
                    "Boundary::has_any_missing_postcondition_kind must delegate verbatim to \
                     postconditions.has_any_missing_kind() for pre={pre_kind:?} post={post_kind:?}",
                );
                let expected_union = !ConditionKind::ALL
                    .iter()
                    .all(|k| pre_kind == *k || post_kind == *k);
                assert_eq!(
                    b.has_any_missing_condition_kind(),
                    expected_union,
                    "Boundary::has_any_missing_condition_kind must equal \
                     !all-ALL-covered-by-either-slice \
                     for pre={pre_kind:?} post={post_kind:?}",
                );
                assert_eq!(
                    b.has_any_missing_condition_kind(),
                    !b.is_condition_kind_saturated(),
                    "Boundary::has_any_missing_condition_kind must equal \
                     !is_condition_kind_saturated() for pre={pre_kind:?} post={post_kind:?}",
                );
            }
        }

        // Saturated boundary — both slices carry every ConditionKind
        // at least once, every arm returns false.
        let mut b = Boundary::default();
        for k in ConditionKind::ALL {
            b.preconditions.push(condition_with(k));
            b.postconditions.push(condition_with(k));
        }
        assert!(
            !b.has_any_missing_precondition_kind(),
            "saturated boundary must return false on has_any_missing_precondition_kind",
        );
        assert!(
            !b.has_any_missing_postcondition_kind(),
            "saturated boundary must return false on has_any_missing_postcondition_kind",
        );
        assert!(
            !b.has_any_missing_condition_kind(),
            "saturated boundary must return false on has_any_missing_condition_kind",
        );
    }

    /// SUBSTRATE-DELEGATION pin (Boundary at-least-one halfspace triad
    /// on the closed-set-inversion axis) — the three
    /// `has_any_distinct_*_condition_kind` methods on [`Boundary`]
    /// delegate to the slice-level substrate primitive
    /// [`ConditionSliceExt::has_any_distinct_kind`] over the two
    /// `Vec<Condition>` slots (precondition + postcondition) and
    /// compose the union via a SHORT-CIRCUITING closed-set walk over
    /// [`ConditionKind::ALL`] under [`Boundary::has_condition_kind`].
    /// Sweeps the empty boundary (every arm returns `false` — no kind
    /// present in either slice), a single-populated-per-side
    /// arrangement (every per-slice arm returns `true`, the union
    /// returns `true`), a single-populated-precondition-only
    /// arrangement (precondition arm `true`, postcondition arm
    /// `false`, union `true`), and the saturated boundary (every arm
    /// returns `true`). Also pins the composition law
    /// `has_any_distinct_*_condition_kind() ==
    /// (distinct_*_condition_kind_count() > 0)` at each arm — a
    /// regression that dropped the short-circuit, drifted the
    /// underlying `has_condition_kind` predicate, or negated the wrong
    /// side surfaces HERE.
    #[test]
    fn has_any_distinct_condition_kind_triad_delegates_to_slice_has_any_distinct_kind() {
        // Empty boundary — every arm returns false (no kind present
        // in either slice; distinct_kind_count == 0 in both).
        let b = Boundary::default();
        assert!(
            !b.has_any_distinct_precondition_kind(),
            "empty boundary must return false on has_any_distinct_precondition_kind",
        );
        assert!(
            !b.has_any_distinct_postcondition_kind(),
            "empty boundary must return false on has_any_distinct_postcondition_kind",
        );
        assert!(
            !b.has_any_distinct_condition_kind(),
            "empty boundary must return false on has_any_distinct_condition_kind",
        );

        // Single-populated per side — sweep ALL × ALL. Every per-slice
        // arm returns true; the union returns true.
        for pre_kind in ConditionKind::ALL {
            for post_kind in ConditionKind::ALL {
                let mut b = Boundary::default();
                b.preconditions.push(condition_with(pre_kind));
                b.postconditions.push(condition_with(post_kind));
                assert_eq!(
                    b.has_any_distinct_precondition_kind(),
                    b.preconditions.has_any_distinct_kind(),
                    "Boundary::has_any_distinct_precondition_kind must delegate verbatim to \
                     preconditions.has_any_distinct_kind() for pre={pre_kind:?} post={post_kind:?}",
                );
                assert_eq!(
                    b.has_any_distinct_postcondition_kind(),
                    b.postconditions.has_any_distinct_kind(),
                    "Boundary::has_any_distinct_postcondition_kind must delegate verbatim to \
                     postconditions.has_any_distinct_kind() for pre={pre_kind:?} post={post_kind:?}",
                );
                assert!(
                    b.has_any_distinct_precondition_kind(),
                    "single-populated preconditions must return true on has_any_distinct_precondition_kind for pre={pre_kind:?}",
                );
                assert!(
                    b.has_any_distinct_postcondition_kind(),
                    "single-populated postconditions must return true on has_any_distinct_postcondition_kind for post={post_kind:?}",
                );
                assert!(
                    b.has_any_distinct_condition_kind(),
                    "single-populated-per-side must return true on has_any_distinct_condition_kind for pre={pre_kind:?} post={post_kind:?}",
                );
            }
        }

        // Single-populated precondition only — precondition arm true,
        // postcondition arm false, union true.
        for pre_kind in ConditionKind::ALL {
            let mut b = Boundary::default();
            b.preconditions.push(condition_with(pre_kind));
            assert!(
                b.has_any_distinct_precondition_kind(),
                "pre-only boundary must return true on has_any_distinct_precondition_kind for pre={pre_kind:?}",
            );
            assert!(
                !b.has_any_distinct_postcondition_kind(),
                "pre-only boundary must return false on has_any_distinct_postcondition_kind for pre={pre_kind:?}",
            );
            assert!(
                b.has_any_distinct_condition_kind(),
                "pre-only boundary must return true on has_any_distinct_condition_kind for pre={pre_kind:?}",
            );
        }

        // Saturated boundary — both slices carry every ConditionKind
        // at least once; every arm returns true.
        let mut b = Boundary::default();
        for k in ConditionKind::ALL {
            b.preconditions.push(condition_with(k));
            b.postconditions.push(condition_with(k));
        }
        assert!(
            b.has_any_distinct_precondition_kind(),
            "saturated boundary must return true on has_any_distinct_precondition_kind",
        );
        assert!(
            b.has_any_distinct_postcondition_kind(),
            "saturated boundary must return true on has_any_distinct_postcondition_kind",
        );
        assert!(
            b.has_any_distinct_condition_kind(),
            "saturated boundary must return true on has_any_distinct_condition_kind",
        );
    }

    /// SUBSTRATE-DELEGATION pin (Boundary singleton-coverage triad on
    /// the closed-set-inversion axis) — the three
    /// `has_unique_distinct_*_condition_kind` methods on [`Boundary`]
    /// delegate to the slice-level substrate primitive
    /// [`ConditionSliceExt::has_unique_distinct_kind`] over the two
    /// `Vec<Condition>` slots (precondition + postcondition) and
    /// compose the union via a two-step-short-circuit walk over
    /// [`ConditionKind::ALL`] under [`Boundary::has_condition_kind`].
    /// Sweeps the empty boundary (every arm returns `false` — 0
    /// distinct, not exactly 1), single-populated-per-side sweeping
    /// ALL × ALL (every per-slice arm returns `true`; the union
    /// returns `true` iff the two kinds coincide OR N == 1), and the
    /// saturated boundary (every arm returns `false` on N ≥ 2 — N
    /// distinct, not exactly 1). Also pins the composition law
    /// `has_unique_distinct_*_condition_kind() ==
    /// (distinct_*_condition_kind_count() == 1)` at each arm — a
    /// regression that dropped the second-slot short-circuit, drifted
    /// the underlying `has_kind` predicate, or conflated with
    /// `has_any_distinct_kind` surfaces HERE.
    #[test]
    fn has_unique_distinct_condition_kind_triad_delegates_to_slice_has_unique_distinct_kind() {
        // Empty boundary — every arm returns false (0 distinct, not
        // exactly 1).
        let b = Boundary::default();
        assert!(
            !b.has_unique_distinct_precondition_kind(),
            "empty boundary must return false on has_unique_distinct_precondition_kind",
        );
        assert!(
            !b.has_unique_distinct_postcondition_kind(),
            "empty boundary must return false on has_unique_distinct_postcondition_kind",
        );
        assert!(
            !b.has_unique_distinct_condition_kind(),
            "empty boundary must return false on has_unique_distinct_condition_kind",
        );
        assert_eq!(
            b.has_unique_distinct_condition_kind(),
            b.distinct_condition_kind_count() == 1,
            "empty has_unique_distinct_condition_kind must equal (distinct_condition_kind_count() == 1)",
        );

        // Single-populated per side — sweep ALL × ALL. Every per-
        // slice arm returns true; the union returns true iff the two
        // populated kinds coincide (union covers 1 kind) OR the
        // closed set is degenerate (N == 1). On this workspace's
        // N == 8 the union returns true iff pre_kind == post_kind.
        for pre_kind in ConditionKind::ALL {
            for post_kind in ConditionKind::ALL {
                let mut b = Boundary::default();
                b.preconditions.push(condition_with(pre_kind));
                b.postconditions.push(condition_with(post_kind));
                assert_eq!(
                    b.has_unique_distinct_precondition_kind(),
                    b.preconditions.has_unique_distinct_kind(),
                    "Boundary::has_unique_distinct_precondition_kind must delegate verbatim to \
                     preconditions.has_unique_distinct_kind() for pre={pre_kind:?} post={post_kind:?}",
                );
                assert_eq!(
                    b.has_unique_distinct_postcondition_kind(),
                    b.postconditions.has_unique_distinct_kind(),
                    "Boundary::has_unique_distinct_postcondition_kind must delegate verbatim to \
                     postconditions.has_unique_distinct_kind() for pre={pre_kind:?} post={post_kind:?}",
                );
                assert!(
                    b.has_unique_distinct_precondition_kind(),
                    "single-populated preconditions must return true on has_unique_distinct_precondition_kind for pre={pre_kind:?}",
                );
                assert!(
                    b.has_unique_distinct_postcondition_kind(),
                    "single-populated postconditions must return true on has_unique_distinct_postcondition_kind for post={post_kind:?}",
                );
                let covered_count = ConditionKind::ALL
                    .into_iter()
                    .filter(|k| *k == pre_kind || *k == post_kind)
                    .count();
                let expected_union = covered_count == 1;
                assert_eq!(
                    b.has_unique_distinct_condition_kind(),
                    expected_union,
                    "Boundary::has_unique_distinct_condition_kind must equal \
                     (covered-ALL-count == 1) for pre={pre_kind:?} post={post_kind:?}",
                );
                assert_eq!(
                    b.has_unique_distinct_condition_kind(),
                    b.distinct_condition_kind_count() == 1,
                    "Boundary::has_unique_distinct_condition_kind must equal \
                     (distinct_condition_kind_count() == 1) for pre={pre_kind:?} post={post_kind:?}",
                );
            }
        }

        // Single-populated precondition only — precondition arm true,
        // postcondition arm false, union true (1 distinct kind).
        for pre_kind in ConditionKind::ALL {
            let mut b = Boundary::default();
            b.preconditions.push(condition_with(pre_kind));
            assert!(
                b.has_unique_distinct_precondition_kind(),
                "pre-only boundary must return true on has_unique_distinct_precondition_kind for pre={pre_kind:?}",
            );
            assert!(
                !b.has_unique_distinct_postcondition_kind(),
                "pre-only boundary must return false on has_unique_distinct_postcondition_kind for pre={pre_kind:?}",
            );
            assert!(
                b.has_unique_distinct_condition_kind(),
                "pre-only boundary must return true on has_unique_distinct_condition_kind for pre={pre_kind:?}",
            );
            assert_eq!(
                b.has_unique_distinct_condition_kind(),
                b.distinct_condition_kind_count() == 1,
                "pre-only has_unique_distinct_condition_kind must equal (distinct_condition_kind_count() == 1) for pre={pre_kind:?}",
            );
        }

        // Saturated boundary — every arm returns false on N ≥ 2 (N
        // distinct, not exactly 1).
        if ConditionKind::ALL.len() >= 2 {
            let mut b = Boundary::default();
            for k in ConditionKind::ALL {
                b.preconditions.push(condition_with(k));
                b.postconditions.push(condition_with(k));
            }
            assert!(
                !b.has_unique_distinct_precondition_kind(),
                "saturated boundary must return false on has_unique_distinct_precondition_kind",
            );
            assert!(
                !b.has_unique_distinct_postcondition_kind(),
                "saturated boundary must return false on has_unique_distinct_postcondition_kind",
            );
            assert!(
                !b.has_unique_distinct_condition_kind(),
                "saturated boundary must return false on has_unique_distinct_condition_kind",
            );
        }
    }

    /// SUBSTRATE-DELEGATION pin (Boundary cardinality-many-arm triad
    /// on the closed-set-inversion axis) — the three
    /// `has_multiple_distinct_*_condition_kind` methods on [`Boundary`]
    /// delegate to the slice-level substrate primitive
    /// [`ConditionSliceExt::has_multiple_distinct_kinds`] over the two
    /// `Vec<Condition>` slots (precondition + postcondition) and
    /// compose the union via a two-step-short-circuit walk over
    /// [`ConditionKind::ALL`] under [`Boundary::has_condition_kind`].
    /// Sweeps the empty boundary (every arm returns `false` — 0
    /// distinct, not ≥ 2), a single-populated-per-side arrangement
    /// (every per-slice arm returns `false` — 1 distinct per slice;
    /// the union returns `true` iff the two kinds DIFFER, otherwise
    /// both coincide and the union has exactly 1 distinct), and the
    /// saturated boundary (every arm returns `true` on `N ≥ 2` — N
    /// distinct, ≥ 2). Also pins the composition law
    /// `has_multiple_distinct_*_condition_kind() ==
    /// (distinct_*_condition_kind_count() >= 2)` at each arm — a
    /// regression that dropped the second-slot short-circuit, drifted
    /// the underlying `has_kind` predicate, or conflated with
    /// `has_any_distinct_kind` surfaces HERE.
    #[test]
    fn has_multiple_distinct_condition_kind_triad_delegates_to_slice_has_multiple_distinct_kinds() {
        // Empty boundary — every arm returns false (0 distinct, not
        // ≥ 2).
        let b = Boundary::default();
        assert!(
            !b.has_multiple_distinct_precondition_kind(),
            "empty boundary must return false on has_multiple_distinct_precondition_kind",
        );
        assert!(
            !b.has_multiple_distinct_postcondition_kind(),
            "empty boundary must return false on has_multiple_distinct_postcondition_kind",
        );
        assert!(
            !b.has_multiple_distinct_condition_kind(),
            "empty boundary must return false on has_multiple_distinct_condition_kind",
        );
        assert_eq!(
            b.has_multiple_distinct_condition_kind(),
            b.distinct_condition_kind_count() >= 2,
            "empty has_multiple_distinct_condition_kind must equal (distinct_condition_kind_count() >= 2)",
        );

        // Single-populated per side — sweep ALL × ALL on N ≥ 2 closed
        // sets. Every per-slice arm returns false (1 distinct per
        // slice, not ≥ 2); the union returns true iff the two kinds
        // DIFFER (covering 2 distinct), otherwise both coincide and
        // the union has exactly 1 distinct.
        assert!(
            ConditionKind::ALL.len() >= 2,
            "test assumes ConditionKind::ALL has ≥ 2 variants",
        );
        for pre_kind in ConditionKind::ALL {
            for post_kind in ConditionKind::ALL {
                let mut b = Boundary::default();
                b.preconditions.push(condition_with(pre_kind));
                b.postconditions.push(condition_with(post_kind));
                assert_eq!(
                    b.has_multiple_distinct_precondition_kind(),
                    b.preconditions.has_multiple_distinct_kinds(),
                    "Boundary::has_multiple_distinct_precondition_kind must delegate verbatim to \
                     preconditions.has_multiple_distinct_kinds() for pre={pre_kind:?} post={post_kind:?}",
                );
                assert_eq!(
                    b.has_multiple_distinct_postcondition_kind(),
                    b.postconditions.has_multiple_distinct_kinds(),
                    "Boundary::has_multiple_distinct_postcondition_kind must delegate verbatim to \
                     postconditions.has_multiple_distinct_kinds() for pre={pre_kind:?} post={post_kind:?}",
                );
                assert!(
                    !b.has_multiple_distinct_precondition_kind(),
                    "single-populated preconditions must return false on has_multiple_distinct_precondition_kind for pre={pre_kind:?}",
                );
                assert!(
                    !b.has_multiple_distinct_postcondition_kind(),
                    "single-populated postconditions must return false on has_multiple_distinct_postcondition_kind for post={post_kind:?}",
                );
                let covered_count = ConditionKind::ALL
                    .into_iter()
                    .filter(|k| *k == pre_kind || *k == post_kind)
                    .count();
                let expected_union = covered_count >= 2;
                assert_eq!(
                    b.has_multiple_distinct_condition_kind(),
                    expected_union,
                    "Boundary::has_multiple_distinct_condition_kind must equal \
                     (covered-ALL-count >= 2) for pre={pre_kind:?} post={post_kind:?}",
                );
                assert_eq!(
                    b.has_multiple_distinct_condition_kind(),
                    b.distinct_condition_kind_count() >= 2,
                    "Boundary::has_multiple_distinct_condition_kind must equal \
                     (distinct_condition_kind_count() >= 2) for pre={pre_kind:?} post={post_kind:?}",
                );
            }
        }

        // Saturated boundary — every arm returns true on N ≥ 2 (N
        // distinct, ≥ 2).
        let mut b = Boundary::default();
        for k in ConditionKind::ALL {
            b.preconditions.push(condition_with(k));
            b.postconditions.push(condition_with(k));
        }
        assert!(
            b.has_multiple_distinct_precondition_kind(),
            "saturated boundary must return true on has_multiple_distinct_precondition_kind",
        );
        assert!(
            b.has_multiple_distinct_postcondition_kind(),
            "saturated boundary must return true on has_multiple_distinct_postcondition_kind",
        );
        assert!(
            b.has_multiple_distinct_condition_kind(),
            "saturated boundary must return true on has_multiple_distinct_condition_kind",
        );
    }

    /// SUBSTRATE-DELEGATION pin (Boundary cardinality "≤ 1" triad on
    /// the closed-set-inversion axis) — the three
    /// `has_at_most_one_distinct_*_condition_kind` methods on
    /// [`Boundary`] delegate to the slice-level substrate primitive
    /// [`ConditionSliceExt::has_at_most_one_distinct_kind`] over the
    /// two `Vec<Condition>` slots (precondition + postcondition) and
    /// compose the union via a definitional negation of the many-arm
    /// two-step-short-circuit walk over [`ConditionKind::ALL`] under
    /// [`Boundary::has_condition_kind`]. Sweeps the empty boundary
    /// (every arm returns `true` — 0 distinct, `≤ 1`), a single-
    /// populated-per-side arrangement (every per-slice arm returns
    /// `true` — 1 distinct per slice, `≤ 1`; the union returns `true`
    /// iff the two kinds COINCIDE, otherwise the union has 2 distinct
    /// and drops to `false`), and the saturated boundary (every arm
    /// returns `false` on `N ≥ 2` — N distinct, not `≤ 1`). Also pins
    /// the composition law `has_at_most_one_distinct_*_condition_kind()
    /// == !has_multiple_distinct_*_condition_kind()` and the widened
    /// composition law
    /// `has_at_most_one_distinct_*_condition_kind() ==
    /// (distinct_*_condition_kind_count() <= 1)` at each arm — a
    /// regression that dropped the definitional negation, drifted the
    /// underlying `has_kind` predicate, or swapped the wrong side of
    /// the negation surfaces HERE.
    #[test]
    fn has_at_most_one_distinct_condition_kind_triad_delegates_to_slice_has_at_most_one_distinct_kind(
    ) {
        // Empty boundary — every arm returns true (0 distinct, ≤ 1).
        let b = Boundary::default();
        assert!(
            b.has_at_most_one_distinct_precondition_kind(),
            "empty boundary must return true on has_at_most_one_distinct_precondition_kind",
        );
        assert!(
            b.has_at_most_one_distinct_postcondition_kind(),
            "empty boundary must return true on has_at_most_one_distinct_postcondition_kind",
        );
        assert!(
            b.has_at_most_one_distinct_condition_kind(),
            "empty boundary must return true on has_at_most_one_distinct_condition_kind",
        );
        assert_eq!(
            b.has_at_most_one_distinct_condition_kind(),
            b.distinct_condition_kind_count() <= 1,
            "empty has_at_most_one_distinct_condition_kind must equal (distinct_condition_kind_count() <= 1)",
        );

        // Single-populated per side — sweep ALL × ALL on N ≥ 2 closed
        // sets. Every per-slice arm returns true (1 distinct per
        // slice, ≤ 1); the union returns true iff the two kinds
        // COINCIDE (union has 1 distinct kind), otherwise the union
        // has 2 distinct kinds and drops to false.
        assert!(
            ConditionKind::ALL.len() >= 2,
            "test assumes ConditionKind::ALL has ≥ 2 variants",
        );
        for pre_kind in ConditionKind::ALL {
            for post_kind in ConditionKind::ALL {
                let mut b = Boundary::default();
                b.preconditions.push(condition_with(pre_kind));
                b.postconditions.push(condition_with(post_kind));
                assert_eq!(
                    b.has_at_most_one_distinct_precondition_kind(),
                    b.preconditions.has_at_most_one_distinct_kind(),
                    "Boundary::has_at_most_one_distinct_precondition_kind must delegate verbatim to \
                     preconditions.has_at_most_one_distinct_kind() for pre={pre_kind:?} post={post_kind:?}",
                );
                assert_eq!(
                    b.has_at_most_one_distinct_postcondition_kind(),
                    b.postconditions.has_at_most_one_distinct_kind(),
                    "Boundary::has_at_most_one_distinct_postcondition_kind must delegate verbatim to \
                     postconditions.has_at_most_one_distinct_kind() for pre={pre_kind:?} post={post_kind:?}",
                );
                assert!(
                    b.has_at_most_one_distinct_precondition_kind(),
                    "single-populated preconditions must return true on has_at_most_one_distinct_precondition_kind for pre={pre_kind:?}",
                );
                assert!(
                    b.has_at_most_one_distinct_postcondition_kind(),
                    "single-populated postconditions must return true on has_at_most_one_distinct_postcondition_kind for post={post_kind:?}",
                );
                let covered_count = ConditionKind::ALL
                    .into_iter()
                    .filter(|k| *k == pre_kind || *k == post_kind)
                    .count();
                let expected_union = covered_count <= 1;
                assert_eq!(
                    b.has_at_most_one_distinct_condition_kind(),
                    expected_union,
                    "Boundary::has_at_most_one_distinct_condition_kind must equal \
                     (covered-ALL-count <= 1) for pre={pre_kind:?} post={post_kind:?}",
                );
                assert_eq!(
                    b.has_at_most_one_distinct_condition_kind(),
                    !b.has_multiple_distinct_condition_kind(),
                    "Boundary::has_at_most_one_distinct_condition_kind must equal \
                     !has_multiple_distinct_condition_kind() for pre={pre_kind:?} post={post_kind:?}",
                );
                assert_eq!(
                    b.has_at_most_one_distinct_condition_kind(),
                    b.distinct_condition_kind_count() <= 1,
                    "Boundary::has_at_most_one_distinct_condition_kind must equal \
                     (distinct_condition_kind_count() <= 1) for pre={pre_kind:?} post={post_kind:?}",
                );
            }
        }

        // Saturated boundary — every arm returns false on N ≥ 2 (N
        // distinct, not ≤ 1).
        let mut b = Boundary::default();
        for k in ConditionKind::ALL {
            b.preconditions.push(condition_with(k));
            b.postconditions.push(condition_with(k));
        }
        assert!(
            !b.has_at_most_one_distinct_precondition_kind(),
            "saturated boundary must return false on has_at_most_one_distinct_precondition_kind",
        );
        assert!(
            !b.has_at_most_one_distinct_postcondition_kind(),
            "saturated boundary must return false on has_at_most_one_distinct_postcondition_kind",
        );
        assert!(
            !b.has_at_most_one_distinct_condition_kind(),
            "saturated boundary must return false on has_at_most_one_distinct_condition_kind",
        );
    }

    /// SUBSTRATE-DELEGATION pin (Boundary cardinality zero-endpoint
    /// triad) — the three `is_*_condition_kind_empty` methods on
    /// [`Boundary`] delegate to the slice-level substrate primitive
    /// [`ConditionSliceExt::is_kind_empty`] over the two
    /// `Vec<Condition>` slots (precondition + postcondition) and
    /// compose the union via a definitional negation of the at-least-
    /// one halfspace primitive
    /// [`Boundary::has_any_distinct_condition_kind`]. Sweeps the empty
    /// boundary (every arm returns `true` — 0 distinct, `= 0`), a
    /// single-populated-per-side arrangement (every per-slice arm
    /// returns `false` — 1 distinct, not `= 0`; the union also returns
    /// `false`), and the saturated boundary (every arm returns `false`
    /// — every kind PRESENT, not `= 0`). Also pins the composition
    /// laws `is_*_condition_kind_empty() ==
    /// (distinct_*_condition_kind_count() == 0)` and
    /// `is_condition_kind_empty() == !has_any_distinct_condition_kind()`
    /// at each arm — a regression that dropped the definitional
    /// negation, drifted the underlying `has_kind` predicate, or
    /// swapped the wrong side of the negation surfaces HERE.
    #[test]
    fn is_condition_kind_empty_triad_delegates_to_slice_is_kind_empty() {
        // Empty boundary — every arm returns true (0 distinct, = 0).
        let b = Boundary::default();
        assert!(
            b.is_precondition_kind_empty(),
            "empty boundary must return true on is_precondition_kind_empty",
        );
        assert!(
            b.is_postcondition_kind_empty(),
            "empty boundary must return true on is_postcondition_kind_empty",
        );
        assert!(
            b.is_condition_kind_empty(),
            "empty boundary must return true on is_condition_kind_empty",
        );
        assert_eq!(
            b.is_condition_kind_empty(),
            b.distinct_condition_kind_count() == 0,
            "empty is_condition_kind_empty must equal (distinct_condition_kind_count() == 0)",
        );
        assert_eq!(
            b.is_condition_kind_empty(),
            !b.has_any_distinct_condition_kind(),
            "empty is_condition_kind_empty must equal !has_any_distinct_condition_kind()",
        );

        // Single-populated per side — every per-slice arm returns
        // false (1 distinct per slice, not = 0); the union always
        // returns false (≥ 1 kind PRESENT across the union).
        assert!(
            !ConditionKind::ALL.is_empty(),
            "test assumes ConditionKind::ALL has ≥ 1 variants",
        );
        for pre_kind in ConditionKind::ALL {
            for post_kind in ConditionKind::ALL {
                let mut b = Boundary::default();
                b.preconditions.push(condition_with(pre_kind));
                b.postconditions.push(condition_with(post_kind));
                assert_eq!(
                    b.is_precondition_kind_empty(),
                    b.preconditions.is_kind_empty(),
                    "Boundary::is_precondition_kind_empty must delegate verbatim to \
                     preconditions.is_kind_empty() for pre={pre_kind:?} post={post_kind:?}",
                );
                assert_eq!(
                    b.is_postcondition_kind_empty(),
                    b.postconditions.is_kind_empty(),
                    "Boundary::is_postcondition_kind_empty must delegate verbatim to \
                     postconditions.is_kind_empty() for pre={pre_kind:?} post={post_kind:?}",
                );
                assert!(
                    !b.is_precondition_kind_empty(),
                    "single-populated preconditions must return false on is_precondition_kind_empty for pre={pre_kind:?}",
                );
                assert!(
                    !b.is_postcondition_kind_empty(),
                    "single-populated postconditions must return false on is_postcondition_kind_empty for post={post_kind:?}",
                );
                assert!(
                    !b.is_condition_kind_empty(),
                    "single-populated union must return false on is_condition_kind_empty for pre={pre_kind:?} post={post_kind:?}",
                );
                assert_eq!(
                    b.is_condition_kind_empty(),
                    !b.has_any_distinct_condition_kind(),
                    "Boundary::is_condition_kind_empty must equal !has_any_distinct_condition_kind() for pre={pre_kind:?} post={post_kind:?}",
                );
                assert_eq!(
                    b.is_condition_kind_empty(),
                    b.distinct_condition_kind_count() == 0,
                    "Boundary::is_condition_kind_empty must equal (distinct_condition_kind_count() == 0) for pre={pre_kind:?} post={post_kind:?}",
                );
            }
        }

        // Saturated boundary — every arm returns false on N ≥ 1 (all
        // kinds PRESENT across the union, not = 0).
        let mut b = Boundary::default();
        for k in ConditionKind::ALL {
            b.preconditions.push(condition_with(k));
            b.postconditions.push(condition_with(k));
        }
        assert!(
            !b.is_precondition_kind_empty(),
            "saturated boundary must return false on is_precondition_kind_empty",
        );
        assert!(
            !b.is_postcondition_kind_empty(),
            "saturated boundary must return false on is_postcondition_kind_empty",
        );
        assert!(
            !b.is_condition_kind_empty(),
            "saturated boundary must return false on is_condition_kind_empty",
        );
    }

    /// SUBSTRATE-DELEGATION pin (Boundary parent-state middle-arm
    /// triad) — the three `is_*_condition_kind_partially_covered`
    /// methods on [`Boundary`] delegate to the slice-level substrate
    /// primitive [`ConditionSliceExt::is_kind_partially_covered`] over
    /// the two `Vec<Condition>` slots (precondition + postcondition)
    /// and compose the union via the paired-halfspace body
    /// `has_any_distinct_condition_kind() && has_any_missing_condition_kind()`.
    /// Sweeps the empty boundary (every arm returns `false` — 0
    /// distinct hits the empty arm, not the middle arm), the saturated
    /// boundary (every arm returns `false` on any `N ≥ 1` — 0 missing
    /// hits the saturated arm, not the middle arm), and single-
    /// populated-per-side arrangements on any `N ≥ 2` closed set
    /// (every per-slice arm returns `true` when the slice carries a
    /// single populated kind; the union returns `true` iff the two
    /// kinds leave at least one uncovered). Also pins the trichotomy
    /// partition law `is_condition_kind_empty +
    /// is_condition_kind_partially_covered + is_condition_kind_saturated
    /// == 1` at each arm — a regression that dropped one bit of the
    /// paired-halfspace walk, drifted the underlying `has_condition_kind`
    /// predicate, or swapped the wrong sides of the composition
    /// surfaces HERE.
    #[test]
    fn is_condition_kind_partially_covered_triad_delegates_to_slice_is_kind_partially_covered() {
        // Empty boundary — every arm returns false on any N ≥ 1
        // closed set (0 distinct hits the empty arm).
        assert!(
            !ConditionKind::ALL.is_empty(),
            "test assumes ConditionKind::ALL has ≥ 1 variants",
        );
        let b = Boundary::default();
        assert!(
            !b.is_precondition_kind_partially_covered(),
            "empty boundary must return false on is_precondition_kind_partially_covered",
        );
        assert!(
            !b.is_postcondition_kind_partially_covered(),
            "empty boundary must return false on is_postcondition_kind_partially_covered",
        );
        assert!(
            !b.is_condition_kind_partially_covered(),
            "empty boundary must return false on is_condition_kind_partially_covered",
        );
        assert_eq!(
            b.is_condition_kind_partially_covered(),
            b.has_any_distinct_condition_kind() && b.has_any_missing_condition_kind(),
            "empty is_condition_kind_partially_covered must equal (has_any_distinct_condition_kind() && has_any_missing_condition_kind())",
        );

        // Single-populated per side — every per-slice arm returns true
        // on any N ≥ 2 closed set (1 distinct + N-1 missing sits in
        // the (open, open) product); the union returns true iff the
        // pre+post kinds leave at least one ALL variant uncovered.
        if ConditionKind::ALL.len() >= 2 {
            for pre_kind in ConditionKind::ALL {
                for post_kind in ConditionKind::ALL {
                    let mut b = Boundary::default();
                    b.preconditions.push(condition_with(pre_kind));
                    b.postconditions.push(condition_with(post_kind));
                    assert_eq!(
                        b.is_precondition_kind_partially_covered(),
                        b.preconditions.is_kind_partially_covered(),
                        "Boundary::is_precondition_kind_partially_covered must delegate verbatim to \
                         preconditions.is_kind_partially_covered() for pre={pre_kind:?} post={post_kind:?}",
                    );
                    assert_eq!(
                        b.is_postcondition_kind_partially_covered(),
                        b.postconditions.is_kind_partially_covered(),
                        "Boundary::is_postcondition_kind_partially_covered must delegate verbatim to \
                         postconditions.is_kind_partially_covered() for pre={pre_kind:?} post={post_kind:?}",
                    );
                    assert!(
                        b.is_precondition_kind_partially_covered(),
                        "single-populated preconditions must return true on is_precondition_kind_partially_covered for pre={pre_kind:?}",
                    );
                    assert!(
                        b.is_postcondition_kind_partially_covered(),
                        "single-populated postconditions must return true on is_postcondition_kind_partially_covered for post={post_kind:?}",
                    );
                    // Union arm — the two kinds cover {pre, post},
                    // partial iff the union leaves ≥ 1 ALL variant
                    // uncovered, which on N ≥ 2 is always true when
                    // pre==post; and when pre!=post, the union is
                    // partial iff |ALL| >= 3 (two covered leaves N-2
                    // uncovered).
                    let covered_count = if pre_kind == post_kind { 1 } else { 2 };
                    let expected_union = ConditionKind::ALL.len() > covered_count;
                    assert_eq!(
                        b.is_condition_kind_partially_covered(),
                        expected_union,
                        "Boundary::is_condition_kind_partially_covered must equal \
                         (ConditionKind::ALL.len() > covered-kinds-count) for pre={pre_kind:?} post={post_kind:?}",
                    );
                    // Trichotomy partition on the union axis.
                    assert_eq!(
                        usize::from(b.is_condition_kind_empty())
                            + usize::from(b.is_condition_kind_partially_covered())
                            + usize::from(b.is_condition_kind_saturated()),
                        1,
                        "Boundary union trichotomy partition violated for pre={pre_kind:?} post={post_kind:?}",
                    );
                }
            }
        }

        // Saturated boundary — every arm returns false on any N ≥ 1
        // closed set (0 missing hits the saturated arm).
        let mut b = Boundary::default();
        for k in ConditionKind::ALL {
            b.preconditions.push(condition_with(k));
            b.postconditions.push(condition_with(k));
        }
        assert!(
            !b.is_precondition_kind_partially_covered(),
            "saturated boundary must return false on is_precondition_kind_partially_covered",
        );
        assert!(
            !b.is_postcondition_kind_partially_covered(),
            "saturated boundary must return false on is_postcondition_kind_partially_covered",
        );
        assert!(
            !b.is_condition_kind_partially_covered(),
            "saturated boundary must return false on is_condition_kind_partially_covered",
        );
        assert_eq!(
            usize::from(b.is_condition_kind_empty())
                + usize::from(b.is_condition_kind_partially_covered())
                + usize::from(b.is_condition_kind_saturated()),
            1,
            "Boundary union trichotomy partition violated on saturated boundary",
        );
    }

    /// SUBSTRATE-DELEGATION pin (Boundary cardinality-mid-endpoint
    /// triad) — the three `has_unique_missing_*_condition_kind`
    /// methods on [`Boundary`] delegate to the slice-level substrate
    /// primitive [`ConditionSliceExt::has_unique_missing_kind`] over
    /// the two `Vec<Condition>` slots (precondition + postcondition)
    /// and compose the union via a two-step-short-circuit walk over
    /// [`ConditionKind::ALL`] under negated
    /// [`Boundary::has_condition_kind`]. Sweeps the empty boundary
    /// (every arm returns `false` — all N missing, not exactly 1),
    /// the near-saturation-endpoint (each slice carries every
    /// [`ConditionKind`] except one — every per-slice arm returns
    /// `true`; the union returns `true` iff BOTH slices omit the SAME
    /// kind), the saturated boundary (every arm returns `false` — 0
    /// missing), and a single-populated-per-side arrangement (every
    /// per-slice arm returns `false` on any `N ≥ 3` closed set; the
    /// union returns `true` only when the two kinds together leave
    /// exactly one kind uncovered). Also pins the composition law
    /// `has_unique_missing_*_condition_kind() ==
    /// (missing_*_condition_kind_count() == 1)` at each arm — a
    /// regression that dropped the second-slot short-circuit, drifted
    /// the underlying `has_kind` predicate, or conflated with
    /// `is_kind_saturated` surfaces HERE.
    #[test]
    fn has_unique_missing_condition_kind_triad_delegates_to_slice_has_unique_missing_kind() {
        // Empty boundary — every arm returns false (all N missing,
        // not exactly 1) on any N ≥ 2 closed set.
        assert!(
            ConditionKind::ALL.len() >= 2,
            "test assumes ConditionKind::ALL has ≥ 2 variants",
        );
        let b = Boundary::default();
        assert!(
            !b.has_unique_missing_precondition_kind(),
            "empty boundary must return false on has_unique_missing_precondition_kind",
        );
        assert!(
            !b.has_unique_missing_postcondition_kind(),
            "empty boundary must return false on has_unique_missing_postcondition_kind",
        );
        assert!(
            !b.has_unique_missing_condition_kind(),
            "empty boundary must return false on has_unique_missing_condition_kind",
        );
        assert_eq!(
            b.has_unique_missing_condition_kind(),
            b.missing_condition_kind_count() == 1,
            "empty has_unique_missing_condition_kind must equal (missing_condition_kind_count() == 1)",
        );

        // Single-populated per side — sweep ALL × ALL on N ≥ 3 closed
        // sets. Every per-slice arm returns false (N - 1 ≥ 2 kinds
        // missing per slice); the union returns true iff the two kinds
        // together leave exactly one ALL variant uncovered.
        if ConditionKind::ALL.len() >= 3 {
            for pre_kind in ConditionKind::ALL {
                for post_kind in ConditionKind::ALL {
                    let mut b = Boundary::default();
                    b.preconditions.push(condition_with(pre_kind));
                    b.postconditions.push(condition_with(post_kind));
                    assert_eq!(
                        b.has_unique_missing_precondition_kind(),
                        b.preconditions.has_unique_missing_kind(),
                        "Boundary::has_unique_missing_precondition_kind must delegate verbatim to \
                         preconditions.has_unique_missing_kind() for pre={pre_kind:?} post={post_kind:?}",
                    );
                    assert_eq!(
                        b.has_unique_missing_postcondition_kind(),
                        b.postconditions.has_unique_missing_kind(),
                        "Boundary::has_unique_missing_postcondition_kind must delegate verbatim to \
                         postconditions.has_unique_missing_kind() for pre={pre_kind:?} post={post_kind:?}",
                    );
                    let uncovered = ConditionKind::ALL
                        .into_iter()
                        .filter(|k| *k != pre_kind && *k != post_kind)
                        .count();
                    let expected_union = uncovered == 1;
                    assert_eq!(
                        b.has_unique_missing_condition_kind(),
                        expected_union,
                        "Boundary::has_unique_missing_condition_kind must equal \
                         (uncovered-ALL-count == 1) for pre={pre_kind:?} post={post_kind:?}",
                    );
                    assert_eq!(
                        b.has_unique_missing_condition_kind(),
                        b.missing_condition_kind_count() == 1,
                        "Boundary::has_unique_missing_condition_kind must equal \
                         (missing_condition_kind_count() == 1) for pre={pre_kind:?} post={post_kind:?}",
                    );
                }
            }
        }

        // Near-saturation-endpoint per side — each slice carries
        // every ConditionKind except one; every per-slice arm returns
        // true. The union returns true iff BOTH slices omit the SAME
        // kind (otherwise the two omissions are covered by each
        // other and the union is saturated).
        for pre_omit in ConditionKind::ALL {
            for post_omit in ConditionKind::ALL {
                let mut b = Boundary::default();
                for k in ConditionKind::ALL {
                    if k != pre_omit {
                        b.preconditions.push(condition_with(k));
                    }
                    if k != post_omit {
                        b.postconditions.push(condition_with(k));
                    }
                }
                assert!(
                    b.has_unique_missing_precondition_kind(),
                    "near-saturation-endpoint precondition slice (omitting {pre_omit:?}) must return true on has_unique_missing_precondition_kind",
                );
                assert!(
                    b.has_unique_missing_postcondition_kind(),
                    "near-saturation-endpoint postcondition slice (omitting {post_omit:?}) must return true on has_unique_missing_postcondition_kind",
                );
                let expected_union = pre_omit == post_omit;
                assert_eq!(
                    b.has_unique_missing_condition_kind(),
                    expected_union,
                    "Boundary::has_unique_missing_condition_kind on both-slices-near-saturated must equal (pre_omit == post_omit) for pre_omit={pre_omit:?} post_omit={post_omit:?}",
                );
                assert_eq!(
                    b.has_unique_missing_condition_kind(),
                    b.missing_condition_kind_count() == 1,
                    "Boundary::has_unique_missing_condition_kind must equal (missing_condition_kind_count() == 1) for pre_omit={pre_omit:?} post_omit={post_omit:?}",
                );
            }
        }

        // Saturated boundary — every arm returns false (0 missing,
        // not exactly 1).
        let mut b = Boundary::default();
        for k in ConditionKind::ALL {
            b.preconditions.push(condition_with(k));
            b.postconditions.push(condition_with(k));
        }
        assert!(
            !b.has_unique_missing_precondition_kind(),
            "saturated boundary must return false on has_unique_missing_precondition_kind",
        );
        assert!(
            !b.has_unique_missing_postcondition_kind(),
            "saturated boundary must return false on has_unique_missing_postcondition_kind",
        );
        assert!(
            !b.has_unique_missing_condition_kind(),
            "saturated boundary must return false on has_unique_missing_condition_kind",
        );
    }

    /// SUBSTRATE-DELEGATION pin (Boundary cardinality-many-arm triad)
    /// — the three `has_multiple_missing_*_condition_kind` methods on
    /// [`Boundary`] delegate to the slice-level substrate primitive
    /// [`ConditionSliceExt::has_multiple_missing_kinds`] over the two
    /// `Vec<Condition>` slots (precondition + postcondition) and
    /// compose the union via a two-step-short-circuit walk over
    /// [`ConditionKind::ALL`] under negated
    /// [`Boundary::has_condition_kind`]. Sweeps the empty boundary
    /// (every arm returns `true` — all N missing, ≥ 2), the near-
    /// saturation-endpoint (each slice carries every
    /// [`ConditionKind`] except one — every per-slice arm returns
    /// `false`; the union returns `true` iff the two slices omit
    /// DIFFERENT kinds), the saturated boundary (every arm returns
    /// `false` — 0 missing), and a single-populated-per-side
    /// arrangement (every per-slice arm returns `true` on any `N ≥ 3`
    /// closed set; the union returns `true` when the two kinds
    /// together leave ≥ 2 kinds uncovered). Also pins the composition
    /// law `has_multiple_missing_*_condition_kind() ==
    /// (missing_*_condition_kind_count() >= 2)` at each arm — a
    /// regression that dropped the second-slot short-circuit, drifted
    /// the underlying `has_kind` predicate, or conflated with
    /// `has_any_missing_kind` surfaces HERE.
    #[test]
    fn has_multiple_missing_condition_kind_triad_delegates_to_slice_has_multiple_missing_kinds() {
        // Empty boundary — every arm returns true (all N missing,
        // ≥ 2) on any N ≥ 2 closed set.
        assert!(
            ConditionKind::ALL.len() >= 2,
            "test assumes ConditionKind::ALL has ≥ 2 variants",
        );
        let b = Boundary::default();
        assert!(
            b.has_multiple_missing_precondition_kind(),
            "empty boundary must return true on has_multiple_missing_precondition_kind",
        );
        assert!(
            b.has_multiple_missing_postcondition_kind(),
            "empty boundary must return true on has_multiple_missing_postcondition_kind",
        );
        assert!(
            b.has_multiple_missing_condition_kind(),
            "empty boundary must return true on has_multiple_missing_condition_kind",
        );
        assert_eq!(
            b.has_multiple_missing_condition_kind(),
            b.missing_condition_kind_count() >= 2,
            "empty has_multiple_missing_condition_kind must equal (missing_condition_kind_count() >= 2)",
        );

        // Single-populated per side — sweep ALL × ALL on N ≥ 3 closed
        // sets. Every per-slice arm returns true (N - 1 ≥ 2 kinds
        // missing per slice); the union returns true iff the two
        // kinds together leave ≥ 2 ALL variants uncovered.
        if ConditionKind::ALL.len() >= 3 {
            for pre_kind in ConditionKind::ALL {
                for post_kind in ConditionKind::ALL {
                    let mut b = Boundary::default();
                    b.preconditions.push(condition_with(pre_kind));
                    b.postconditions.push(condition_with(post_kind));
                    assert_eq!(
                        b.has_multiple_missing_precondition_kind(),
                        b.preconditions.has_multiple_missing_kinds(),
                        "Boundary::has_multiple_missing_precondition_kind must delegate verbatim to \
                         preconditions.has_multiple_missing_kinds() for pre={pre_kind:?} post={post_kind:?}",
                    );
                    assert_eq!(
                        b.has_multiple_missing_postcondition_kind(),
                        b.postconditions.has_multiple_missing_kinds(),
                        "Boundary::has_multiple_missing_postcondition_kind must delegate verbatim to \
                         postconditions.has_multiple_missing_kinds() for pre={pre_kind:?} post={post_kind:?}",
                    );
                    let uncovered = ConditionKind::ALL
                        .into_iter()
                        .filter(|k| *k != pre_kind && *k != post_kind)
                        .count();
                    let expected_union = uncovered >= 2;
                    assert_eq!(
                        b.has_multiple_missing_condition_kind(),
                        expected_union,
                        "Boundary::has_multiple_missing_condition_kind must equal \
                         (uncovered-ALL-count >= 2) for pre={pre_kind:?} post={post_kind:?}",
                    );
                    assert_eq!(
                        b.has_multiple_missing_condition_kind(),
                        b.missing_condition_kind_count() >= 2,
                        "Boundary::has_multiple_missing_condition_kind must equal \
                         (missing_condition_kind_count() >= 2) for pre={pre_kind:?} post={post_kind:?}",
                    );
                }
            }
        }

        // Near-saturation-endpoint per side — each slice carries
        // every ConditionKind except one; every per-slice arm returns
        // false (exactly 1 missing per slice, not ≥ 2). The union
        // returns true iff the two slices omit DIFFERENT kinds
        // (otherwise both omissions coincide and the union has
        // exactly 1 missing, not ≥ 2).
        for pre_omit in ConditionKind::ALL {
            for post_omit in ConditionKind::ALL {
                let mut b = Boundary::default();
                for k in ConditionKind::ALL {
                    if k != pre_omit {
                        b.preconditions.push(condition_with(k));
                    }
                    if k != post_omit {
                        b.postconditions.push(condition_with(k));
                    }
                }
                assert!(
                    !b.has_multiple_missing_precondition_kind(),
                    "near-saturation-endpoint precondition slice (omitting {pre_omit:?}) must return false on has_multiple_missing_precondition_kind",
                );
                assert!(
                    !b.has_multiple_missing_postcondition_kind(),
                    "near-saturation-endpoint postcondition slice (omitting {post_omit:?}) must return false on has_multiple_missing_postcondition_kind",
                );
                // Union: pre-only-missing = {pre_omit}, post-only-
                // missing = {post_omit}. Union missing = both
                // omissions ∩ each other only when they coincide.
                let expected_union = false;
                assert_eq!(
                    b.has_multiple_missing_condition_kind(),
                    expected_union,
                    "Boundary::has_multiple_missing_condition_kind on both-slices-near-saturated must always be false (union missing ≤ 1) for pre_omit={pre_omit:?} post_omit={post_omit:?}",
                );
                assert_eq!(
                    b.has_multiple_missing_condition_kind(),
                    b.missing_condition_kind_count() >= 2,
                    "Boundary::has_multiple_missing_condition_kind must equal (missing_condition_kind_count() >= 2) for pre_omit={pre_omit:?} post_omit={post_omit:?}",
                );
            }
        }

        // Saturated boundary — every arm returns false (0 missing,
        // not ≥ 2).
        let mut b = Boundary::default();
        for k in ConditionKind::ALL {
            b.preconditions.push(condition_with(k));
            b.postconditions.push(condition_with(k));
        }
        assert!(
            !b.has_multiple_missing_precondition_kind(),
            "saturated boundary must return false on has_multiple_missing_precondition_kind",
        );
        assert!(
            !b.has_multiple_missing_postcondition_kind(),
            "saturated boundary must return false on has_multiple_missing_postcondition_kind",
        );
        assert!(
            !b.has_multiple_missing_condition_kind(),
            "saturated boundary must return false on has_multiple_missing_condition_kind",
        );
    }

    /// SUBSTRATE-DELEGATION pin (Boundary cardinality "≤ 1" triad) —
    /// the three `has_at_most_one_missing_*_condition_kind` methods on
    /// [`Boundary`] delegate to the slice-level substrate primitive
    /// [`ConditionSliceExt::has_at_most_one_missing_kind`] over the
    /// two `Vec<Condition>` slots (precondition + postcondition) and
    /// compose the union via
    /// `!self.has_multiple_missing_condition_kind()` — a definitional
    /// negation of the many-arm union primitive. Sweeps the empty
    /// boundary (every arm returns `false` — `N ≥ 2` missing, not
    /// `≤ 1`), the near-saturation-endpoint (each slice carries
    /// every [`ConditionKind`] except one — every per-slice arm
    /// returns `true`; the union returns `true` — since the union of
    /// two near-saturated slices always has `≤ 1` missing), the
    /// saturated boundary (every arm returns `true` — 0 missing,
    /// `≤ 1`), and a single-populated-per-side arrangement (every
    /// per-slice arm returns `false` on any `N ≥ 3` closed set; the
    /// union returns `true` iff the two kinds together leave `≤ 1`
    /// kind uncovered — the near-saturation-endpoint of the union
    /// axis). Also pins the composition law
    /// `has_at_most_one_missing_*_condition_kind() ==
    /// (missing_*_condition_kind_count() <= 1)` at each arm — a
    /// regression that dropped the definitional negation (returning
    /// `has_multiple_missing_condition_kind` itself), swapped the
    /// wrong side, or drifted the trichotomy union operator from
    /// `||` to `&&` surfaces HERE.
    #[test]
    fn has_at_most_one_missing_condition_kind_triad_delegates_to_slice_has_at_most_one_missing_kind(
    ) {
        // Empty boundary — every arm returns false (all N missing,
        // not ≤ 1) on any N ≥ 2 closed set.
        assert!(
            ConditionKind::ALL.len() >= 2,
            "test assumes ConditionKind::ALL has ≥ 2 variants",
        );
        let b = Boundary::default();
        assert!(
            !b.has_at_most_one_missing_precondition_kind(),
            "empty boundary must return false on has_at_most_one_missing_precondition_kind",
        );
        assert!(
            !b.has_at_most_one_missing_postcondition_kind(),
            "empty boundary must return false on has_at_most_one_missing_postcondition_kind",
        );
        assert!(
            !b.has_at_most_one_missing_condition_kind(),
            "empty boundary must return false on has_at_most_one_missing_condition_kind",
        );
        assert_eq!(
            b.has_at_most_one_missing_condition_kind(),
            b.missing_condition_kind_count() <= 1,
            "empty has_at_most_one_missing_condition_kind must equal (missing_condition_kind_count() <= 1)",
        );

        // Single-populated per side — sweep ALL × ALL on N ≥ 3
        // closed sets. Every per-slice arm returns false (N - 1 ≥ 2
        // kinds missing per slice, not ≤ 1); the union returns true
        // iff the two kinds together leave ≤ 1 ALL variant
        // uncovered — the near-saturation-endpoint of the union
        // axis.
        if ConditionKind::ALL.len() >= 3 {
            for pre_kind in ConditionKind::ALL {
                for post_kind in ConditionKind::ALL {
                    let mut b = Boundary::default();
                    b.preconditions.push(condition_with(pre_kind));
                    b.postconditions.push(condition_with(post_kind));
                    assert_eq!(
                        b.has_at_most_one_missing_precondition_kind(),
                        b.preconditions.has_at_most_one_missing_kind(),
                        "Boundary::has_at_most_one_missing_precondition_kind must delegate verbatim to \
                         preconditions.has_at_most_one_missing_kind() for pre={pre_kind:?} post={post_kind:?}",
                    );
                    assert_eq!(
                        b.has_at_most_one_missing_postcondition_kind(),
                        b.postconditions.has_at_most_one_missing_kind(),
                        "Boundary::has_at_most_one_missing_postcondition_kind must delegate verbatim to \
                         postconditions.has_at_most_one_missing_kind() for pre={pre_kind:?} post={post_kind:?}",
                    );
                    let uncovered = ConditionKind::ALL
                        .into_iter()
                        .filter(|k| *k != pre_kind && *k != post_kind)
                        .count();
                    let expected_union = uncovered <= 1;
                    assert_eq!(
                        b.has_at_most_one_missing_condition_kind(),
                        expected_union,
                        "Boundary::has_at_most_one_missing_condition_kind must equal \
                         (uncovered-ALL-count <= 1) for pre={pre_kind:?} post={post_kind:?}",
                    );
                    assert_eq!(
                        b.has_at_most_one_missing_condition_kind(),
                        !b.has_multiple_missing_condition_kind(),
                        "Boundary::has_at_most_one_missing_condition_kind must equal \
                         !has_multiple_missing_condition_kind() for pre={pre_kind:?} post={post_kind:?}",
                    );
                    assert_eq!(
                        b.has_at_most_one_missing_condition_kind(),
                        b.missing_condition_kind_count() <= 1,
                        "Boundary::has_at_most_one_missing_condition_kind must equal \
                         (missing_condition_kind_count() <= 1) for pre={pre_kind:?} post={post_kind:?}",
                    );
                }
            }
        }

        // Near-saturation-endpoint per side — each slice carries
        // every ConditionKind except one; every per-slice arm returns
        // true (exactly 1 missing per slice, ≤ 1). The union has ≤ 1
        // missing whether or not the two omissions coincide, so the
        // union is always true on this arm.
        for pre_omit in ConditionKind::ALL {
            for post_omit in ConditionKind::ALL {
                let mut b = Boundary::default();
                for k in ConditionKind::ALL {
                    if k != pre_omit {
                        b.preconditions.push(condition_with(k));
                    }
                    if k != post_omit {
                        b.postconditions.push(condition_with(k));
                    }
                }
                assert!(
                    b.has_at_most_one_missing_precondition_kind(),
                    "near-saturation-endpoint precondition slice (omitting {pre_omit:?}) must return true on has_at_most_one_missing_precondition_kind",
                );
                assert!(
                    b.has_at_most_one_missing_postcondition_kind(),
                    "near-saturation-endpoint postcondition slice (omitting {post_omit:?}) must return true on has_at_most_one_missing_postcondition_kind",
                );
                assert!(
                    b.has_at_most_one_missing_condition_kind(),
                    "Boundary::has_at_most_one_missing_condition_kind on both-slices-near-saturated must always be true (union missing ≤ 1) for pre_omit={pre_omit:?} post_omit={post_omit:?}",
                );
                assert_eq!(
                    b.has_at_most_one_missing_condition_kind(),
                    b.missing_condition_kind_count() <= 1,
                    "Boundary::has_at_most_one_missing_condition_kind must equal (missing_condition_kind_count() <= 1) for pre_omit={pre_omit:?} post_omit={post_omit:?}",
                );
            }
        }

        // Saturated boundary — every arm returns true (0 missing,
        // ≤ 1).
        let mut b = Boundary::default();
        for k in ConditionKind::ALL {
            b.preconditions.push(condition_with(k));
            b.postconditions.push(condition_with(k));
        }
        assert!(
            b.has_at_most_one_missing_precondition_kind(),
            "saturated boundary must return true on has_at_most_one_missing_precondition_kind",
        );
        assert!(
            b.has_at_most_one_missing_postcondition_kind(),
            "saturated boundary must return true on has_at_most_one_missing_postcondition_kind",
        );
        assert!(
            b.has_at_most_one_missing_condition_kind(),
            "saturated boundary must return true on has_at_most_one_missing_condition_kind",
        );
    }

    /// SUBSTRATE-DELEGATION pin (Boundary per-kind-complement triad) —
    /// the three `lacks_*_condition_kind` methods on [`Boundary`]
    /// delegate to the slice-level substrate primitive
    /// [`ConditionSliceExt::lacks_kind`] over the two `Vec<Condition>`
    /// slots (precondition + postcondition) and compose the union via
    /// `!self.has_condition_kind(kind)`. Sweeps the empty boundary
    /// (every arm returns `true` for every kind), a single-populated-
    /// per-side arrangement (per-slice arms return `false` on the
    /// populated kind + `true` on every other kind; the union returns
    /// `false` iff EITHER slice populates the addressed kind), and the
    /// saturated boundary (both slices carry every [`ConditionKind`],
    /// every arm returns `false` for every kind). Also pins the
    /// composition laws `lacks_*_condition_kind(k) ==
    /// !has_*_condition_kind(k)` at each arm AND `lacks_condition_kind(k)
    /// == lacks_precondition_kind(k) && lacks_postcondition_kind(k)`
    /// (the union AND-composition dual of `has`'s OR-composition) — a
    /// regression that dropped the negation, drifted the union operator
    /// to `||`, or negated the wrong side surfaces HERE.
    #[test]
    fn lacks_condition_kind_triad_delegates_to_slice_lacks_kind() {
        // Empty boundary — every arm returns true on every kind.
        let b = Boundary::default();
        for kind in ConditionKind::ALL {
            assert!(
                b.lacks_precondition_kind(kind),
                "empty boundary must return true on lacks_precondition_kind for {kind:?}",
            );
            assert!(
                b.lacks_postcondition_kind(kind),
                "empty boundary must return true on lacks_postcondition_kind for {kind:?}",
            );
            assert!(
                b.lacks_condition_kind(kind),
                "empty boundary must return true on lacks_condition_kind for {kind:?}",
            );
            assert_eq!(
                b.lacks_condition_kind(kind),
                !b.has_condition_kind(kind),
                "empty lacks_condition_kind must equal !has_condition_kind for {kind:?}",
            );
        }

        // Single-populated per side — sweep ALL × ALL, then probe every
        // ConditionKind on the (pre, post, union) triad.
        for pre_kind in ConditionKind::ALL {
            for post_kind in ConditionKind::ALL {
                let mut b = Boundary::default();
                b.preconditions.push(condition_with(pre_kind));
                b.postconditions.push(condition_with(post_kind));
                for probe in ConditionKind::ALL {
                    assert_eq!(
                        b.lacks_precondition_kind(probe),
                        b.preconditions.lacks_kind(probe),
                        "Boundary::lacks_precondition_kind must delegate verbatim to preconditions.lacks_kind for pre={pre_kind:?} post={post_kind:?} probe={probe:?}",
                    );
                    assert_eq!(
                        b.lacks_postcondition_kind(probe),
                        b.postconditions.lacks_kind(probe),
                        "Boundary::lacks_postcondition_kind must delegate verbatim to postconditions.lacks_kind for pre={pre_kind:?} post={post_kind:?} probe={probe:?}",
                    );
                    let expected_union = pre_kind != probe && post_kind != probe;
                    assert_eq!(
                        b.lacks_condition_kind(probe),
                        expected_union,
                        "Boundary::lacks_condition_kind must equal all-ALL-absent-in-both-slices for pre={pre_kind:?} post={post_kind:?} probe={probe:?}",
                    );
                    assert_eq!(
                        b.lacks_condition_kind(probe),
                        !b.has_condition_kind(probe),
                        "Boundary::lacks_condition_kind must equal !has_condition_kind for pre={pre_kind:?} post={post_kind:?} probe={probe:?}",
                    );
                    assert_eq!(
                        b.lacks_condition_kind(probe),
                        b.lacks_precondition_kind(probe)
                            && b.lacks_postcondition_kind(probe),
                        "Boundary::lacks_condition_kind must equal AND-of-half-slice-arms for pre={pre_kind:?} post={post_kind:?} probe={probe:?}",
                    );
                }
            }
        }

        // Saturated boundary — both slices carry every ConditionKind,
        // every arm returns false on every kind.
        let mut b = Boundary::default();
        for k in ConditionKind::ALL {
            b.preconditions.push(condition_with(k));
            b.postconditions.push(condition_with(k));
        }
        for kind in ConditionKind::ALL {
            assert!(
                !b.lacks_precondition_kind(kind),
                "saturated boundary must return false on lacks_precondition_kind for {kind:?}",
            );
            assert!(
                !b.lacks_postcondition_kind(kind),
                "saturated boundary must return false on lacks_postcondition_kind for {kind:?}",
            );
            assert!(
                !b.lacks_condition_kind(kind),
                "saturated boundary must return false on lacks_condition_kind for {kind:?}",
            );
        }
    }

    /// TRIAD delegation pin — the (precondition, postcondition,
    /// condition-union) kind-scoped strict-refinement triad on
    /// [`Boundary`] agrees byte-for-byte with the slice-level
    /// substrate primitive [`ConditionSliceExt::has_only_kind`] on
    /// every authored arrangement.
    ///
    /// Sweeps [`ConditionKind::ALL`] × [`ConditionKind::ALL`] over
    /// single-populated-per-side arrangements (the well-formed
    /// diagonal), probing every [`ConditionKind`] at the union arm
    /// against the DERIVED oracle
    /// `boundary.distinct_condition_kinds() == vec![probe]` — a
    /// regression at the union arm's fused walk (dropping the
    /// short-circuit, swapping the `saw_kind` arm, mis-composing the
    /// `||` union at [`Boundary::has_condition_kind`]) surfaces HERE
    /// rather than as silent drift at every downstream `has-only-
    /// <kind>` require-tag classifier or well-formed-diagonal
    /// coherence check callsite. Also pins the per-slice arms
    /// delegate verbatim to
    /// [`ConditionSliceExt::has_only_kind`] over the corresponding
    /// half-slice.
    #[test]
    fn has_only_condition_kind_triad_delegates_to_slice_has_only_kind() {
        // Empty boundary — every arm returns false on every kind
        // (no kind is populated, so no kind is "only").
        let b = Boundary::default();
        for kind in ConditionKind::ALL {
            assert!(
                !b.has_only_precondition_kind(kind),
                "empty boundary must return false on has_only_precondition_kind for {kind:?}",
            );
            assert!(
                !b.has_only_postcondition_kind(kind),
                "empty boundary must return false on has_only_postcondition_kind for {kind:?}",
            );
            assert!(
                !b.has_only_condition_kind(kind),
                "empty boundary must return false on has_only_condition_kind for {kind:?}",
            );
        }

        // Single-populated per side — sweep ALL × ALL, then probe
        // every ConditionKind on the (pre, post, union) triad. The
        // union arm returns `true` iff the addressed kind matches
        // BOTH the (nonempty) pre kind AND the (nonempty) post kind;
        // any (pre_kind, post_kind) with `pre_kind != post_kind`
        // yields `false` on every union arm.
        for pre_kind in ConditionKind::ALL {
            for post_kind in ConditionKind::ALL {
                let mut b = Boundary::default();
                b.preconditions.push(condition_with(pre_kind));
                b.postconditions.push(condition_with(post_kind));
                for probe in ConditionKind::ALL {
                    assert_eq!(
                        b.has_only_precondition_kind(probe),
                        b.preconditions.has_only_kind(probe),
                        "Boundary::has_only_precondition_kind must delegate verbatim to preconditions.has_only_kind for pre={pre_kind:?} post={post_kind:?} probe={probe:?}",
                    );
                    assert_eq!(
                        b.has_only_postcondition_kind(probe),
                        b.postconditions.has_only_kind(probe),
                        "Boundary::has_only_postcondition_kind must delegate verbatim to postconditions.has_only_kind for pre={pre_kind:?} post={post_kind:?} probe={probe:?}",
                    );
                    let expected_union = pre_kind == probe && post_kind == probe;
                    assert_eq!(
                        b.has_only_condition_kind(probe),
                        expected_union,
                        "Boundary::has_only_condition_kind must equal (pre_kind == probe && post_kind == probe) for pre={pre_kind:?} post={post_kind:?} probe={probe:?}",
                    );
                    assert_eq!(
                        b.has_only_condition_kind(probe),
                        b.distinct_condition_kinds() == vec![probe],
                        "Boundary::has_only_condition_kind({probe:?}) must equal (distinct_condition_kinds() == vec![{probe:?}]) for pre={pre_kind:?} post={post_kind:?}",
                    );
                }
            }
        }

        // Single-side-only populated — a boundary with a condition on
        // ONE side and NOTHING on the other: the union carries a
        // singleton distinct set. The single-slice AND-of-strict-
        // refinement fails on the empty side (`empty.has_only_kind(k)
        // == false`), but the union arm returns `true` for the
        // populated kind — pins that the union arm reaches the union
        // primitive, not the (pre AND post) AND-composition.
        for populated in ConditionKind::ALL {
            let mut b = Boundary::default();
            b.preconditions.push(condition_with(populated));
            for probe in ConditionKind::ALL {
                let expected = probe == populated;
                assert_eq!(
                    b.has_only_condition_kind(probe),
                    expected,
                    "pre-only boundary populated={populated:?} must return {expected} on has_only_condition_kind({probe:?})",
                );
                assert_eq!(
                    b.has_only_condition_kind(probe),
                    b.distinct_condition_kinds() == vec![probe],
                    "pre-only boundary populated={populated:?} must agree with distinct_condition_kinds() == vec![{probe:?}]",
                );
            }
            let mut b = Boundary::default();
            b.postconditions.push(condition_with(populated));
            for probe in ConditionKind::ALL {
                let expected = probe == populated;
                assert_eq!(
                    b.has_only_condition_kind(probe),
                    expected,
                    "post-only boundary populated={populated:?} must return {expected} on has_only_condition_kind({probe:?})",
                );
                assert_eq!(
                    b.has_only_condition_kind(probe),
                    b.distinct_condition_kinds() == vec![probe],
                    "post-only boundary populated={populated:?} must agree with distinct_condition_kinds() == vec![{probe:?}]",
                );
            }
        }

        // Saturated boundary — both slices carry every ConditionKind,
        // every arm returns false on every kind (N distinct kinds, no
        // kind is "only").
        let mut b = Boundary::default();
        for k in ConditionKind::ALL {
            b.preconditions.push(condition_with(k));
            b.postconditions.push(condition_with(k));
        }
        for kind in ConditionKind::ALL {
            assert!(
                !b.has_only_precondition_kind(kind),
                "saturated boundary must return false on has_only_precondition_kind for {kind:?}",
            );
            assert!(
                !b.has_only_postcondition_kind(kind),
                "saturated boundary must return false on has_only_postcondition_kind for {kind:?}",
            );
            assert!(
                !b.has_only_condition_kind(kind),
                "saturated boundary must return false on has_only_condition_kind for {kind:?}",
            );
        }
    }

    /// TRIAD delegation pin — the (precondition, postcondition,
    /// condition-union) kind-scoped strict-refinement-on-missing triad
    /// on [`Boundary`] agrees byte-for-byte with the slice-level
    /// substrate primitive [`ConditionSliceExt::lacks_only_kind`] on
    /// every authored arrangement.
    ///
    /// Sweeps [`ConditionKind::ALL`] × [`ConditionKind::ALL`] over
    /// single-populated-per-side arrangements + near-saturation-per-
    /// side arrangements (the union arm's well-formed missing
    /// diagonal), probing every [`ConditionKind`] at the union arm
    /// against the DERIVED oracle
    /// `boundary.missing_condition_kinds() == vec![probe]` — a
    /// regression at the union arm's fused walk (dropping the
    /// short-circuit, swapping the `saw_kind` arm, mis-composing the
    /// `has_condition_kind` complement) surfaces HERE rather than as
    /// silent drift at every downstream `lacks-only-<kind>` require-
    /// tag classifier or near-saturation-diagonal coherence check
    /// callsite. Also pins the per-slice arms delegate verbatim to
    /// [`ConditionSliceExt::lacks_only_kind`] over the corresponding
    /// half-slice.
    #[test]
    fn lacks_only_condition_kind_triad_delegates_to_slice_lacks_only_kind() {
        // Empty boundary — every kind is missing from the union
        // (2 ≥ N missing on any N ≥ 2), so no kind is "only" missing.
        let b = Boundary::default();
        for kind in ConditionKind::ALL {
            assert_eq!(
                b.lacks_only_precondition_kind(kind),
                b.preconditions.lacks_only_kind(kind),
                "empty boundary lacks_only_precondition_kind must delegate to preconditions.lacks_only_kind for {kind:?}",
            );
            assert_eq!(
                b.lacks_only_postcondition_kind(kind),
                b.postconditions.lacks_only_kind(kind),
                "empty boundary lacks_only_postcondition_kind must delegate to postconditions.lacks_only_kind for {kind:?}",
            );
            assert!(
                !b.lacks_only_condition_kind(kind),
                "empty boundary must return false on lacks_only_condition_kind for {kind:?} (every kind is missing on N ≥ 2)",
            );
        }

        // Single-populated per side — sweep ALL × ALL, then probe
        // every ConditionKind on the (pre, post, union) triad. The
        // per-slice arms return `false` (on N ≥ 3 the slice has ≥ 2
        // missing kinds; on N == 2 the missing set is single-element
        // but only for the OTHER kind). The union arm returns `false`
        // for every kind on N ≥ 3 — the union missing set has size
        // `N - |{pre, post}|` which is ≥ 2 whenever N ≥ 3, or size 1
        // iff pre != post (union covers both), or size N - 1 iff
        // pre == post.
        for pre_kind in ConditionKind::ALL {
            for post_kind in ConditionKind::ALL {
                let mut b = Boundary::default();
                b.preconditions.push(condition_with(pre_kind));
                b.postconditions.push(condition_with(post_kind));
                for probe in ConditionKind::ALL {
                    assert_eq!(
                        b.lacks_only_precondition_kind(probe),
                        b.preconditions.lacks_only_kind(probe),
                        "Boundary::lacks_only_precondition_kind must delegate verbatim to preconditions.lacks_only_kind for pre={pre_kind:?} post={post_kind:?} probe={probe:?}",
                    );
                    assert_eq!(
                        b.lacks_only_postcondition_kind(probe),
                        b.postconditions.lacks_only_kind(probe),
                        "Boundary::lacks_only_postcondition_kind must delegate verbatim to postconditions.lacks_only_kind for pre={pre_kind:?} post={post_kind:?} probe={probe:?}",
                    );
                    assert_eq!(
                        b.lacks_only_condition_kind(probe),
                        b.missing_condition_kinds() == vec![probe],
                        "Boundary::lacks_only_condition_kind({probe:?}) must equal (missing_condition_kinds() == vec![{probe:?}]) for pre={pre_kind:?} post={post_kind:?}",
                    );
                }
            }
        }

        // Near-saturation per side — build a boundary whose preconditions
        // carry every kind except one, sweep every "omitted" kind for the
        // pre side, then probe the per-slice arm. On the well-formed
        // near-saturation diagonal (missing == {omitted}),
        // preconditions.lacks_only_kind(omitted) == true; every other
        // arm is false.
        for omitted in ConditionKind::ALL {
            let mut b = Boundary::default();
            for k in ConditionKind::ALL {
                if k != omitted {
                    b.preconditions.push(condition_with(k));
                    b.postconditions.push(condition_with(k));
                }
            }
            for probe in ConditionKind::ALL {
                let expected = probe == omitted;
                assert_eq!(
                    b.lacks_only_precondition_kind(probe),
                    expected,
                    "near-saturation boundary omitted={omitted:?} must return {expected} on lacks_only_precondition_kind({probe:?})",
                );
                assert_eq!(
                    b.lacks_only_postcondition_kind(probe),
                    expected,
                    "near-saturation boundary omitted={omitted:?} must return {expected} on lacks_only_postcondition_kind({probe:?})",
                );
                assert_eq!(
                    b.lacks_only_condition_kind(probe),
                    expected,
                    "near-saturation boundary omitted={omitted:?} must return {expected} on lacks_only_condition_kind({probe:?})",
                );
                assert_eq!(
                    b.lacks_only_condition_kind(probe),
                    b.missing_condition_kinds() == vec![probe],
                    "near-saturation boundary omitted={omitted:?} must agree with missing_condition_kinds() == vec![{probe:?}]",
                );
            }
        }

        // Single-side-only near-saturation — a boundary whose ONE side
        // carries every kind except one, the OTHER side empty: the
        // empty side is missing every kind (per-slice `lacks_only_kind`
        // returns false on N ≥ 2), but the union covers everything the
        // populated side does, so the union missing set is still
        // `{omitted}` and the union arm returns `true` for `omitted`.
        // Pins that the union arm reaches the union primitive, not the
        // (pre AND post) AND-composition (which would fail on the
        // empty side).
        for omitted in ConditionKind::ALL {
            let mut b = Boundary::default();
            for k in ConditionKind::ALL {
                if k != omitted {
                    b.preconditions.push(condition_with(k));
                }
            }
            for probe in ConditionKind::ALL {
                let expected = probe == omitted;
                assert_eq!(
                    b.lacks_only_condition_kind(probe),
                    expected,
                    "pre-only near-saturation boundary omitted={omitted:?} must return {expected} on lacks_only_condition_kind({probe:?})",
                );
                assert_eq!(
                    b.lacks_only_condition_kind(probe),
                    b.missing_condition_kinds() == vec![probe],
                    "pre-only near-saturation boundary omitted={omitted:?} must agree with missing_condition_kinds() == vec![{probe:?}]",
                );
            }
            let mut b = Boundary::default();
            for k in ConditionKind::ALL {
                if k != omitted {
                    b.postconditions.push(condition_with(k));
                }
            }
            for probe in ConditionKind::ALL {
                let expected = probe == omitted;
                assert_eq!(
                    b.lacks_only_condition_kind(probe),
                    expected,
                    "post-only near-saturation boundary omitted={omitted:?} must return {expected} on lacks_only_condition_kind({probe:?})",
                );
            }
        }

        // Saturated boundary — every kind populated in the union, so
        // no kind is missing, so `lacks_only_kind` returns false on
        // every arm.
        let mut b = Boundary::default();
        for k in ConditionKind::ALL {
            b.preconditions.push(condition_with(k));
            b.postconditions.push(condition_with(k));
        }
        for kind in ConditionKind::ALL {
            assert!(
                !b.lacks_only_precondition_kind(kind),
                "saturated boundary must return false on lacks_only_precondition_kind for {kind:?}",
            );
            assert!(
                !b.lacks_only_postcondition_kind(kind),
                "saturated boundary must return false on lacks_only_postcondition_kind for {kind:?}",
            );
            assert!(
                !b.lacks_only_condition_kind(kind),
                "saturated boundary must return false on lacks_only_condition_kind for {kind:?}",
            );
        }
    }

    // ── assert_slice_refinement_composition_laws — substrate testkit ──
    //
    // The substrate testkit primitive
    // [`assert_slice_refinement_composition_laws`] pins the FOUR
    // composition laws that bind the [`ConditionSliceExt`] refinement
    // algebra (find ↔ iter, count ↔ iter, has ↔ find, has ↔ count) at
    // ONE call site per authored arrangement, sweeping
    // [`ConditionKind::ALL`]. The four hand-authored slice-level
    // composition-law tests above
    // (`condition_slice_find_kind_equals_iter_kind_next`,
    // `condition_slice_count_kind_equals_iter_kind_count`,
    // `condition_slice_has_kind_equals_find_kind_is_some`,
    // `condition_slice_has_and_find_equal_count_greater_than_zero`)
    // stay as first-class per-law drift-arm pins; this substrate
    // testkit is the compound-lift primitive that binds all four
    // laws through ONE typed sweep so a future FIFTH refinement's
    // composition law picks up its pin as ONE new arm inside the
    // primitive's body rather than as ONE new sibling test at every
    // downstream author-time enumeration.

    /// SUBSTRATE PANEL pin — the substrate testkit primitive
    /// [`assert_slice_refinement_composition_laws`] passes on the
    /// FOUR canonical authored arrangements the trait's downstream
    /// consumers reach for: the empty slice (every refinement returns
    /// its zero-element identity), a single-element populated slice
    /// (every refinement returns the addressed match's projection),
    /// a dual-populated slice with distinct kinds (every refinement
    /// probes the kind field per element), and a duplicate-populated
    /// slice with the same kind at multiple positions (the widened
    /// primitive `iter_kind` yields every match; `find_kind` collapses
    /// to the first; `count_kind` returns the exact cardinality;
    /// `has_kind` returns true). Sweeping the four arrangements at
    /// ONE call site pins that every composition law holds regardless
    /// of the widened primitive's yield structure.
    #[test]
    fn slice_refinement_composition_laws_hold_across_authored_arrangements() {
        let empty: &[Condition] = &[];
        assert_slice_refinement_composition_laws(empty);

        for populated in ConditionKind::ALL {
            let single = [condition_with(populated)];
            assert_slice_refinement_composition_laws(single.as_slice());
        }

        for pre_kind in ConditionKind::ALL {
            for post_kind in ConditionKind::ALL {
                let dual = [condition_with(pre_kind), condition_with(post_kind)];
                assert_slice_refinement_composition_laws(dual.as_slice());
            }
        }

        for populated in ConditionKind::ALL {
            let duplicates = [
                condition_with(populated),
                condition_with(populated),
                condition_with(populated),
            ];
            assert_slice_refinement_composition_laws(duplicates.as_slice());
        }
    }

    /// SUBSTRATE PANEL pin (params-distinguishable duplicates) — the
    /// substrate primitive holds on a slice that carries duplicate
    /// kinds interleaved with a distinct kind, byte-for-byte peer of
    /// the standalone `condition_slice_iter_kind_yields_every_match_in_slice_order_on_duplicates`
    /// / `condition_slice_count_kind_counts_every_match_on_duplicates`
    /// arrangement. Confirms the four composition laws hold when
    /// the widened primitive's yield stream is genuinely multi-element
    /// AND the addressed kind is interleaved with a non-matching kind
    /// (the union structural case that the diagonal-and-corners sweep
    /// above doesn't reach).
    #[test]
    fn slice_refinement_composition_laws_hold_on_interleaved_duplicates() {
        let interleaved = [
            Condition {
                kind: ConditionKind::ClosedLoopAuth,
                params: json!({ "probeImage": "first" }),
            },
            Condition {
                kind: ConditionKind::PromQL,
                params: json!({ "query": "up" }),
            },
            Condition {
                kind: ConditionKind::ClosedLoopAuth,
                params: json!({ "probeImage": "second" }),
            },
            Condition {
                kind: ConditionKind::PromQL,
                params: json!({ "query": "healthy" }),
            },
            Condition {
                kind: ConditionKind::ClosedLoopAuth,
                params: json!({ "probeImage": "third" }),
            },
        ];
        assert_slice_refinement_composition_laws(interleaved.as_slice());
    }

    // ── assert_surface_union_composition_laws — substrate testkit ────
    //
    // The substrate testkit macro
    // [`crate::assert_surface_union_composition_laws`] pins the FOUR
    // union composition laws (has: OR, find: or_else, iter: chain,
    // count: SUM) that bind the (pre, post, union) refinement triads
    // on the [`Boundary`] surface at ONE call site per authored
    // arrangement, sweeping [`ConditionKind::ALL`]. The four hand-
    // authored point-surface composition-law tests above
    // (`boundary_has_condition_kind_composes_precondition_and_postcondition_arms`,
    // `find_condition_kind_triad_delegates_to_slice_find_kind`,
    // `iter_condition_kind_triad_delegates_to_slice_iter_kind`,
    // `boundary_count_condition_kind_triad_delegates_and_sums_slice_count_kind`)
    // stay as first-class per-law drift-arm pins; this substrate
    // testkit macro is the compound-lift primitive that binds all
    // four union composition laws through ONE typed sweep so a
    // future FIFTH union refinement picks up its composition-law
    // pin as ONE new arm inside the macro body rather than as ONE
    // new sibling test at every downstream author-time
    // enumeration on each of the two surfaces.

    /// SUBSTRATE PANEL pin — the substrate testkit macro
    /// [`crate::assert_surface_union_composition_laws`] passes on
    /// [`Boundary`] for the four canonical authored arrangements the
    /// surface's downstream consumers reach for: the empty boundary
    /// (every union arm returns its zero-element identity), a
    /// precondition-only populated boundary (every union arm equals
    /// its precondition arm, postcondition arm is empty), a
    /// postcondition-only populated boundary (mirror), and a dual-
    /// populated boundary sweeping `ALL × ALL` (both half-slice arms
    /// contribute; the union monoid operator applies). Sweeping the
    /// four arrangements at ONE call site pins every union
    /// composition law holds regardless of the arrangement's per-
    /// half fill pattern.
    #[test]
    fn boundary_surface_union_composition_laws_hold_across_authored_arrangements() {
        let empty = Boundary::default();
        crate::assert_surface_union_composition_laws!(empty);

        for populated in ConditionKind::ALL {
            let mut pre_only = Boundary::default();
            pre_only.preconditions.push(condition_with(populated));
            crate::assert_surface_union_composition_laws!(pre_only);

            let mut post_only = Boundary::default();
            post_only.postconditions.push(condition_with(populated));
            crate::assert_surface_union_composition_laws!(post_only);
        }

        for pre_kind in ConditionKind::ALL {
            for post_kind in ConditionKind::ALL {
                let mut dual = Boundary::default();
                dual.preconditions.push(condition_with(pre_kind));
                dual.postconditions.push(condition_with(post_kind));
                crate::assert_surface_union_composition_laws!(dual);
            }
        }
    }

    /// SUBSTRATE PANEL pin (params-distinguishable duplicates) — the
    /// substrate macro holds on a [`Boundary`] whose two half-slices
    /// each carry duplicates of the same kind at multiple positions,
    /// interleaved with a distinct kind. The scenario reaches every
    /// union arm at its non-degenerate composition: `has` still
    /// resolves `true` on both halves (OR is not the discriminating
    /// bit), `find` yields the FIRST-precondition-side match
    /// (`or_else` walk order), `iter` yields every match with the
    /// full pre-then-post chain order (five total matches across the
    /// two halves), `count` returns the SUM (five). A regression that
    /// (a) collapsed `find`'s `or_else` to `and_then` (silently
    /// narrowing to intersection), (b) collapsed `iter`'s `chain` to
    /// `zip` (silently truncating to `min(pre, post)`), or (c)
    /// collapsed `count`'s SUM to `max` (silently narrowing the
    /// cardinality) surfaces HERE — the four laws are pinned
    /// simultaneously and any single-arm regression fails one of
    /// the four asserts.
    #[test]
    fn boundary_surface_union_composition_laws_hold_on_interleaved_duplicates() {
        let mut b = Boundary::default();
        b.preconditions.push(Condition {
            kind: ConditionKind::ClosedLoopAuth,
            params: json!({ "side": "pre-1" }),
        });
        b.preconditions.push(Condition {
            kind: ConditionKind::PromQL,
            params: json!({ "query": "up" }),
        });
        b.preconditions.push(Condition {
            kind: ConditionKind::ClosedLoopAuth,
            params: json!({ "side": "pre-2" }),
        });
        b.postconditions.push(Condition {
            kind: ConditionKind::PromQL,
            params: json!({ "query": "healthy" }),
        });
        b.postconditions.push(Condition {
            kind: ConditionKind::ClosedLoopAuth,
            params: json!({ "side": "post-1" }),
        });
        crate::assert_surface_union_composition_laws!(b);
    }

    /// SUBSTRATE-DELEGATION pin (Boundary unique-distinct-kind
    /// witnessing triad on the closed-set-inversion axis) — the three
    /// `unique_distinct_*_condition_kind` methods on [`Boundary`]
    /// delegate to the slice-level substrate primitive
    /// [`ConditionSliceExt::unique_distinct_kind`] over the two
    /// `Vec<Condition>` slots (precondition + postcondition) and
    /// compose the union via a two-step-short-circuit walk over
    /// [`ConditionKind::ALL`] under [`Boundary::has_condition_kind`].
    /// Sweep `ConditionKind::ALL × ConditionKind::ALL` so a regression
    /// that (a) dropped the second-hit short-circuit (returning
    /// `Some(first)` on a two-distinct union), (b) inlined a divergent
    /// closed-set walk at either half-slice arm, or (c) diverged the
    /// witness scalar from the Boolean predicate surfaces HERE. Also
    /// pins the composition laws `unique_distinct_*_kind().is_some() ==
    /// has_unique_distinct_*_kind()` and (on the `Some` arm)
    /// `unique_distinct_*_kind() == first_distinct_*_kind() ==
    /// last_distinct_*_kind()` at each arm.
    #[test]
    fn unique_distinct_condition_kind_triad_delegates_to_slice_unique_distinct_kind() {
        // Empty boundary — every arm returns None.
        let b = Boundary::default();
        assert_eq!(
            b.unique_distinct_precondition_kind(),
            None,
            "empty boundary must return None on unique_distinct_precondition_kind",
        );
        assert_eq!(
            b.unique_distinct_postcondition_kind(),
            None,
            "empty boundary must return None on unique_distinct_postcondition_kind",
        );
        assert_eq!(
            b.unique_distinct_condition_kind(),
            None,
            "empty boundary must return None on unique_distinct_condition_kind",
        );

        for pre_kind in ConditionKind::ALL {
            for post_kind in ConditionKind::ALL {
                let mut b = Boundary::default();
                b.preconditions.push(condition_with(pre_kind));
                b.postconditions.push(condition_with(post_kind));

                assert_eq!(
                    b.unique_distinct_precondition_kind(),
                    b.preconditions.unique_distinct_kind(),
                    "Boundary::unique_distinct_precondition_kind must delegate verbatim to \
                     preconditions.unique_distinct_kind() for pre={pre_kind:?} post={post_kind:?}",
                );
                assert_eq!(
                    b.unique_distinct_precondition_kind(),
                    Some(pre_kind),
                    "Boundary::unique_distinct_precondition_kind must equal Some(pre_kind) on \
                     single-populated preconditions for pre={pre_kind:?} post={post_kind:?}",
                );
                assert_eq!(
                    b.unique_distinct_postcondition_kind(),
                    b.postconditions.unique_distinct_kind(),
                    "Boundary::unique_distinct_postcondition_kind must delegate verbatim to \
                     postconditions.unique_distinct_kind() for pre={pre_kind:?} post={post_kind:?}",
                );
                assert_eq!(
                    b.unique_distinct_postcondition_kind(),
                    Some(post_kind),
                    "Boundary::unique_distinct_postcondition_kind must equal Some(post_kind) on \
                     single-populated postconditions for pre={pre_kind:?} post={post_kind:?}",
                );

                // Union arm: Some(k) iff the union covers exactly one kind.
                let covered: Vec<ConditionKind> = ConditionKind::ALL
                    .into_iter()
                    .filter(|k| pre_kind == *k || post_kind == *k)
                    .collect();
                let expected_union = if covered.len() == 1 {
                    Some(covered[0])
                } else {
                    None
                };
                assert_eq!(
                    b.unique_distinct_condition_kind(),
                    expected_union,
                    "Boundary::unique_distinct_condition_kind must equal Some(k) iff the \
                     ALL-entries covered by either half-slice sum to exactly one for \
                     pre={pre_kind:?} post={post_kind:?}",
                );

                // Boolean-witness composition laws.
                assert_eq!(
                    b.unique_distinct_condition_kind().is_some(),
                    b.has_unique_distinct_condition_kind(),
                    "unique_distinct_condition_kind().is_some() must equal \
                     has_unique_distinct_condition_kind() for pre={pre_kind:?} post={post_kind:?}",
                );
                assert_eq!(
                    b.unique_distinct_precondition_kind().is_some(),
                    b.has_unique_distinct_precondition_kind(),
                    "unique_distinct_precondition_kind().is_some() must equal \
                     has_unique_distinct_precondition_kind() for pre={pre_kind:?} post={post_kind:?}",
                );
                assert_eq!(
                    b.unique_distinct_postcondition_kind().is_some(),
                    b.has_unique_distinct_postcondition_kind(),
                    "unique_distinct_postcondition_kind().is_some() must equal \
                     has_unique_distinct_postcondition_kind() for pre={pre_kind:?} post={post_kind:?}",
                );

                // Endpoint-agreement — on Some, first == last == unique.
                if let Some(k) = b.unique_distinct_condition_kind() {
                    assert_eq!(
                        b.first_distinct_condition_kind(),
                        Some(k),
                        "unique_distinct_condition_kind() Some arm must equal \
                         first_distinct_condition_kind() for pre={pre_kind:?} post={post_kind:?}",
                    );
                    assert_eq!(
                        b.last_distinct_condition_kind(),
                        Some(k),
                        "unique_distinct_condition_kind() Some arm must equal \
                         last_distinct_condition_kind() for pre={pre_kind:?} post={post_kind:?}",
                    );
                }
            }
        }

        // Saturated boundary — every arm returns None on N ≥ 2.
        if ConditionKind::ALL.len() >= 2 {
            let mut b = Boundary::default();
            for k in ConditionKind::ALL {
                b.preconditions.push(condition_with(k));
                b.postconditions.push(condition_with(k));
            }
            assert_eq!(
                b.unique_distinct_precondition_kind(),
                None,
                "saturated boundary must return None on unique_distinct_precondition_kind",
            );
            assert_eq!(
                b.unique_distinct_postcondition_kind(),
                None,
                "saturated boundary must return None on unique_distinct_postcondition_kind",
            );
            assert_eq!(
                b.unique_distinct_condition_kind(),
                None,
                "saturated boundary must return None on unique_distinct_condition_kind",
            );
        }
    }

    /// SUBSTRATE-DELEGATION pin (Boundary unique-missing-kind
    /// witnessing triad on the closed-set-complement axis) — the three
    /// `unique_missing_*_condition_kind` methods on [`Boundary`]
    /// delegate to the slice-level substrate primitive
    /// [`ConditionSliceExt::unique_missing_kind`] over the two
    /// `Vec<Condition>` slots (precondition + postcondition) and
    /// compose the union via a two-step-short-circuit walk over
    /// [`ConditionKind::ALL`] under a NEGATED
    /// [`Boundary::has_condition_kind`]. Sweep `ConditionKind::ALL ×
    /// ConditionKind::ALL` so a regression that dropped the negation,
    /// dropped the second-hit short-circuit, or diverged the witness
    /// scalar from the Boolean predicate surfaces HERE. Also pins the
    /// composition laws `unique_missing_*_kind().is_some() ==
    /// has_unique_missing_*_kind()` and (on the `Some` arm)
    /// `unique_missing_*_kind() == first_missing_*_kind() ==
    /// last_missing_*_kind()` at each arm.
    #[test]
    fn unique_missing_condition_kind_triad_delegates_to_slice_unique_missing_kind() {
        // Empty boundary — every arm returns None on N ≥ 2 (every
        // kind missing, not exactly 1).
        let b = Boundary::default();
        if ConditionKind::ALL.len() >= 2 {
            assert_eq!(
                b.unique_missing_precondition_kind(),
                None,
                "empty boundary must return None on unique_missing_precondition_kind \
                 on any N ≥ 2 closed set",
            );
            assert_eq!(
                b.unique_missing_postcondition_kind(),
                None,
                "empty boundary must return None on unique_missing_postcondition_kind \
                 on any N ≥ 2 closed set",
            );
            assert_eq!(
                b.unique_missing_condition_kind(),
                None,
                "empty boundary must return None on unique_missing_condition_kind \
                 on any N ≥ 2 closed set",
            );
        }

        for pre_kind in ConditionKind::ALL {
            for post_kind in ConditionKind::ALL {
                let mut b = Boundary::default();
                b.preconditions.push(condition_with(pre_kind));
                b.postconditions.push(condition_with(post_kind));

                assert_eq!(
                    b.unique_missing_precondition_kind(),
                    b.preconditions.unique_missing_kind(),
                    "Boundary::unique_missing_precondition_kind must delegate verbatim to \
                     preconditions.unique_missing_kind() for pre={pre_kind:?} post={post_kind:?}",
                );
                assert_eq!(
                    b.unique_missing_postcondition_kind(),
                    b.postconditions.unique_missing_kind(),
                    "Boundary::unique_missing_postcondition_kind must delegate verbatim to \
                     postconditions.unique_missing_kind() for pre={pre_kind:?} post={post_kind:?}",
                );

                // Union arm: Some(k) iff the union is missing exactly one kind.
                let missing: Vec<ConditionKind> = ConditionKind::ALL
                    .into_iter()
                    .filter(|k| pre_kind != *k && post_kind != *k)
                    .collect();
                let expected_union = if missing.len() == 1 {
                    Some(missing[0])
                } else {
                    None
                };
                assert_eq!(
                    b.unique_missing_condition_kind(),
                    expected_union,
                    "Boundary::unique_missing_condition_kind must equal Some(k) iff the \
                     ALL-entries NOT covered by either half-slice sum to exactly one for \
                     pre={pre_kind:?} post={post_kind:?}",
                );

                // Boolean-witness composition laws.
                assert_eq!(
                    b.unique_missing_condition_kind().is_some(),
                    b.has_unique_missing_condition_kind(),
                    "unique_missing_condition_kind().is_some() must equal \
                     has_unique_missing_condition_kind() for pre={pre_kind:?} post={post_kind:?}",
                );
                assert_eq!(
                    b.unique_missing_precondition_kind().is_some(),
                    b.has_unique_missing_precondition_kind(),
                    "unique_missing_precondition_kind().is_some() must equal \
                     has_unique_missing_precondition_kind() for pre={pre_kind:?} post={post_kind:?}",
                );
                assert_eq!(
                    b.unique_missing_postcondition_kind().is_some(),
                    b.has_unique_missing_postcondition_kind(),
                    "unique_missing_postcondition_kind().is_some() must equal \
                     has_unique_missing_postcondition_kind() for pre={pre_kind:?} post={post_kind:?}",
                );

                // Endpoint-agreement — on Some, first == last == unique.
                if let Some(k) = b.unique_missing_condition_kind() {
                    assert_eq!(
                        b.first_missing_condition_kind(),
                        Some(k),
                        "unique_missing_condition_kind() Some arm must equal \
                         first_missing_condition_kind() for pre={pre_kind:?} post={post_kind:?}",
                    );
                    assert_eq!(
                        b.last_missing_condition_kind(),
                        Some(k),
                        "unique_missing_condition_kind() Some arm must equal \
                         last_missing_condition_kind() for pre={pre_kind:?} post={post_kind:?}",
                    );
                }
            }
        }

        // Saturated boundary — every arm returns None (zero missing).
        let mut b = Boundary::default();
        for k in ConditionKind::ALL {
            b.preconditions.push(condition_with(k));
            b.postconditions.push(condition_with(k));
        }
        assert_eq!(
            b.unique_missing_precondition_kind(),
            None,
            "saturated boundary must return None on unique_missing_precondition_kind",
        );
        assert_eq!(
            b.unique_missing_postcondition_kind(),
            None,
            "saturated boundary must return None on unique_missing_postcondition_kind",
        );
        assert_eq!(
            b.unique_missing_condition_kind(),
            None,
            "saturated boundary must return None on unique_missing_condition_kind",
        );

        // Near-saturation arm: exactly one ALL entry missing on each
        // side (achieved by populating every kind except `hole`).
        for hole in ConditionKind::ALL {
            let mut b = Boundary::default();
            for k in ConditionKind::ALL {
                if k != hole {
                    b.preconditions.push(condition_with(k));
                    b.postconditions.push(condition_with(k));
                }
            }
            assert_eq!(
                b.unique_missing_precondition_kind(),
                Some(hole),
                "near-saturation boundary must return Some(hole={hole:?}) on unique_missing_precondition_kind",
            );
            assert_eq!(
                b.unique_missing_postcondition_kind(),
                Some(hole),
                "near-saturation boundary must return Some(hole={hole:?}) on unique_missing_postcondition_kind",
            );
            assert_eq!(
                b.unique_missing_condition_kind(),
                Some(hole),
                "near-saturation boundary must return Some(hole={hole:?}) on unique_missing_condition_kind",
            );
        }
    }

    /// SUBSTRATE-DELEGATION pin (Boundary per-kind cardinality "≥ 2"
    /// many-arm triad on the count axis) — the three
    /// `has_multiple_of_*_condition_kind` methods on [`Boundary`]
    /// delegate to the slice-level substrate primitive
    /// [`ConditionSliceExt::has_multiple_of_kind`] over the two
    /// `Vec<Condition>` slots (precondition + postcondition) and
    /// compose the union via a two-step-short-circuit walk over the
    /// chained per-kind iterator [`Boundary::iter_condition_kind`].
    /// Sweeps: (a) the empty boundary (every arm returns `false` on
    /// every kind — 0 matches, not ≥ 2); (b) a
    /// single-populated-per-side arrangement where each per-slice
    /// arm returns `false` (1 match per slice) but the union returns
    /// `true` iff the two kinds COINCIDE (2 matches on the shared
    /// kind); (c) a double-populated postcondition (post arm returns
    /// `true`, pre arm returns `false`, union returns `true`); (d)
    /// the saturated-doubled boundary (every arm returns `true` on
    /// every kind — every slice carries every kind twice). Also pins
    /// the composition law
    /// `has_multiple_of_*_condition_kind(k) ==
    ///  (count_*_condition_kind(k) >= 2)` at each arm.
    #[test]
    fn has_multiple_of_condition_kind_triad_delegates_to_slice_has_multiple_of_kind() {
        // Empty boundary — every arm returns false on every kind.
        let b = Boundary::default();
        for kind in ConditionKind::ALL {
            assert!(
                !b.has_multiple_of_precondition_kind(kind),
                "empty boundary must return false on has_multiple_of_precondition_kind({kind:?})",
            );
            assert!(
                !b.has_multiple_of_postcondition_kind(kind),
                "empty boundary must return false on has_multiple_of_postcondition_kind({kind:?})",
            );
            assert!(
                !b.has_multiple_of_condition_kind(kind),
                "empty boundary must return false on has_multiple_of_condition_kind({kind:?})",
            );
            assert_eq!(
                b.has_multiple_of_condition_kind(kind),
                b.count_condition_kind(kind) >= 2,
                "empty has_multiple_of_condition_kind({kind:?}) must equal \
                 (count_condition_kind >= 2)",
            );
        }

        // Single-populated-per-side sweep — per-slice arms stay
        // false; union goes true iff pre and post carry the SAME
        // kind (chain sums to 2 matches on the shared kind).
        for pre_kind in ConditionKind::ALL {
            for post_kind in ConditionKind::ALL {
                let mut b = Boundary::default();
                b.preconditions.push(condition_with(pre_kind));
                b.postconditions.push(condition_with(post_kind));

                assert_eq!(
                    b.has_multiple_of_precondition_kind(pre_kind),
                    b.preconditions.has_multiple_of_kind(pre_kind),
                    "Boundary::has_multiple_of_precondition_kind must delegate verbatim to \
                     preconditions.has_multiple_of_kind for pre={pre_kind:?} post={post_kind:?}",
                );
                assert_eq!(
                    b.has_multiple_of_postcondition_kind(post_kind),
                    b.postconditions.has_multiple_of_kind(post_kind),
                    "Boundary::has_multiple_of_postcondition_kind must delegate verbatim to \
                     postconditions.has_multiple_of_kind for pre={pre_kind:?} post={post_kind:?}",
                );

                for query in ConditionKind::ALL {
                    assert!(
                        !b.has_multiple_of_precondition_kind(query),
                        "single-populated preconditions must return false on \
                         has_multiple_of_precondition_kind({query:?}) for \
                         pre={pre_kind:?} post={post_kind:?}",
                    );
                    assert!(
                        !b.has_multiple_of_postcondition_kind(query),
                        "single-populated postconditions must return false on \
                         has_multiple_of_postcondition_kind({query:?}) for \
                         pre={pre_kind:?} post={post_kind:?}",
                    );
                    let expected_union = pre_kind == query && post_kind == query;
                    assert_eq!(
                        b.has_multiple_of_condition_kind(query),
                        expected_union,
                        "Boundary::has_multiple_of_condition_kind({query:?}) must equal \
                         (pre_kind == query && post_kind == query) for \
                         pre={pre_kind:?} post={post_kind:?}",
                    );
                    assert_eq!(
                        b.has_multiple_of_condition_kind(query),
                        b.count_condition_kind(query) >= 2,
                        "Boundary::has_multiple_of_condition_kind({query:?}) drifted from \
                         (count_condition_kind >= 2) for pre={pre_kind:?} post={post_kind:?}",
                    );
                }
            }
        }

        // Double-populated postcondition — post arm goes true on
        // the doubled kind, pre arm stays false, union goes true.
        for doubled in ConditionKind::ALL {
            let mut b = Boundary::default();
            b.postconditions.push(condition_with(doubled));
            b.postconditions.push(condition_with(doubled));

            assert!(
                !b.has_multiple_of_precondition_kind(doubled),
                "empty preconditions must return false on has_multiple_of_precondition_kind \
                 for doubled={doubled:?}",
            );
            assert!(
                b.has_multiple_of_postcondition_kind(doubled),
                "doubled postconditions must return true on has_multiple_of_postcondition_kind \
                 for doubled={doubled:?}",
            );
            assert!(
                b.has_multiple_of_condition_kind(doubled),
                "doubled postconditions must return true on union has_multiple_of_condition_kind \
                 for doubled={doubled:?}",
            );
            for query in ConditionKind::ALL {
                if query != doubled {
                    assert!(
                        !b.has_multiple_of_condition_kind(query),
                        "other kind {query:?} must return false on union has_multiple_of_condition_kind \
                         when only {doubled:?} is doubled",
                    );
                }
            }
        }

        // Saturated-doubled boundary — every arm returns true on
        // every kind (every slice carries every kind twice).
        let mut b = Boundary::default();
        for k in ConditionKind::ALL {
            b.preconditions.push(condition_with(k));
            b.preconditions.push(condition_with(k));
            b.postconditions.push(condition_with(k));
            b.postconditions.push(condition_with(k));
        }
        for kind in ConditionKind::ALL {
            assert!(
                b.has_multiple_of_precondition_kind(kind),
                "saturated-doubled boundary must return true on has_multiple_of_precondition_kind({kind:?})",
            );
            assert!(
                b.has_multiple_of_postcondition_kind(kind),
                "saturated-doubled boundary must return true on has_multiple_of_postcondition_kind({kind:?})",
            );
            assert!(
                b.has_multiple_of_condition_kind(kind),
                "saturated-doubled boundary must return true on has_multiple_of_condition_kind({kind:?})",
            );
        }
    }

    /// Every arm of the (precondition, postcondition, condition-union)
    /// per-kind cardinality "= 1" mid-endpoint triad on [`Boundary`]
    /// delegates verbatim to the slice-level substrate primitive
    /// [`ConditionSliceExt::has_unique_of_kind`]. Sweeps four
    /// arrangements: (a) an empty boundary (every arm returns
    /// `false` on every kind); (b) a single-populated-per-side sweep
    /// where per-slice arms fire iff their kind equals `query`,
    /// while the union arm fires iff EXACTLY ONE of `{pre, post}`
    /// equals `query` (the other side either lacks the kind, giving
    /// 1 chain match, or shares it, giving 2 chain matches — only
    /// the disjoint-arm case yields `= 1`); (c) a double-populated
    /// postcondition (post arm returns `false` on the doubled kind
    /// as `≥ 2` matches, pre arm returns `false` on 0 matches,
    /// union returns `false` on `≥ 2` chain matches); (d) the
    /// saturated-singleton boundary (every kind appears exactly
    /// once on every slice — per-slice arms return `true` on every
    /// kind, union returns `false` on every kind as `= 2` chain
    /// matches). Also pins the composition law
    /// `has_unique_of_*_condition_kind(k) ==
    ///  (count_*_condition_kind(k) == 1)` at each arm and the
    /// trichotomy partition
    /// {lacks, has_unique_of, has_multiple_of}_condition_kind
    /// firing EXACTLY ONE arm at the union level.
    #[test]
    fn has_unique_of_condition_kind_triad_delegates_to_slice_has_unique_of_kind() {
        // Empty boundary — every arm returns false on every kind.
        let b = Boundary::default();
        for kind in ConditionKind::ALL {
            assert!(
                !b.has_unique_of_precondition_kind(kind),
                "empty boundary must return false on has_unique_of_precondition_kind({kind:?})",
            );
            assert!(
                !b.has_unique_of_postcondition_kind(kind),
                "empty boundary must return false on has_unique_of_postcondition_kind({kind:?})",
            );
            assert!(
                !b.has_unique_of_condition_kind(kind),
                "empty boundary must return false on has_unique_of_condition_kind({kind:?})",
            );
            assert_eq!(
                b.has_unique_of_condition_kind(kind),
                b.count_condition_kind(kind) == 1,
                "empty has_unique_of_condition_kind({kind:?}) must equal \
                 (count_condition_kind == 1)",
            );
        }

        // Single-populated-per-side sweep — per-slice arm returns
        // true iff its side's kind equals `query`. Union arm returns
        // true iff EXACTLY ONE of `{pre, post}` equals `query`
        // (chain sums to 1 on the disjoint-arm case, 2 on shared,
        // 0 on unrelated).
        for pre_kind in ConditionKind::ALL {
            for post_kind in ConditionKind::ALL {
                let mut b = Boundary::default();
                b.preconditions.push(condition_with(pre_kind));
                b.postconditions.push(condition_with(post_kind));

                for query in ConditionKind::ALL {
                    assert_eq!(
                        b.has_unique_of_precondition_kind(query),
                        b.preconditions.has_unique_of_kind(query),
                        "Boundary::has_unique_of_precondition_kind must delegate verbatim to \
                         preconditions.has_unique_of_kind for pre={pre_kind:?} \
                         post={post_kind:?} query={query:?}",
                    );
                    assert_eq!(
                        b.has_unique_of_postcondition_kind(query),
                        b.postconditions.has_unique_of_kind(query),
                        "Boundary::has_unique_of_postcondition_kind must delegate verbatim to \
                         postconditions.has_unique_of_kind for pre={pre_kind:?} \
                         post={post_kind:?} query={query:?}",
                    );

                    let pre_hit = pre_kind == query;
                    let post_hit = post_kind == query;
                    let expected_union = pre_hit ^ post_hit;
                    assert_eq!(
                        b.has_unique_of_condition_kind(query),
                        expected_union,
                        "Boundary::has_unique_of_condition_kind({query:?}) must equal \
                         (pre_hit XOR post_hit) for pre={pre_kind:?} post={post_kind:?}",
                    );
                    assert_eq!(
                        b.has_unique_of_condition_kind(query),
                        b.count_condition_kind(query) == 1,
                        "Boundary::has_unique_of_condition_kind({query:?}) drifted from \
                         (count_condition_kind == 1) for pre={pre_kind:?} post={post_kind:?}",
                    );

                    // Trichotomy partition pin at the union level.
                    let arms_true = [
                        b.lacks_condition_kind(query),
                        b.has_unique_of_condition_kind(query),
                        b.has_multiple_of_condition_kind(query),
                    ]
                    .into_iter()
                    .filter(|&x| x)
                    .count();
                    assert_eq!(
                        arms_true, 1,
                        "per-kind trichotomy at boundary union for query={query:?} \
                         (pre={pre_kind:?} post={post_kind:?}) must fire EXACTLY one \
                         arm, got {arms_true}",
                    );
                }
            }
        }

        // Double-populated postcondition — post arm returns false
        // on the doubled kind (≥ 2 matches), pre arm returns false
        // (0 matches), union returns false (2 chain matches).
        for doubled in ConditionKind::ALL {
            let mut b = Boundary::default();
            b.postconditions.push(condition_with(doubled));
            b.postconditions.push(condition_with(doubled));

            assert!(
                !b.has_unique_of_precondition_kind(doubled),
                "empty preconditions must return false on has_unique_of_precondition_kind \
                 for doubled={doubled:?}",
            );
            assert!(
                !b.has_unique_of_postcondition_kind(doubled),
                "doubled postconditions must return false on has_unique_of_postcondition_kind \
                 for doubled={doubled:?}",
            );
            assert!(
                !b.has_unique_of_condition_kind(doubled),
                "doubled postconditions must return false on union has_unique_of_condition_kind \
                 for doubled={doubled:?}",
            );
        }

        // Saturated-singleton boundary — every kind appears exactly
        // once on every slice. Per-slice arms return true on every
        // kind; union returns false on every kind (= 2 chain matches).
        let mut b = Boundary::default();
        for k in ConditionKind::ALL {
            b.preconditions.push(condition_with(k));
            b.postconditions.push(condition_with(k));
        }
        for kind in ConditionKind::ALL {
            assert!(
                b.has_unique_of_precondition_kind(kind),
                "saturated-singleton boundary must return true on has_unique_of_precondition_kind({kind:?})",
            );
            assert!(
                b.has_unique_of_postcondition_kind(kind),
                "saturated-singleton boundary must return true on has_unique_of_postcondition_kind({kind:?})",
            );
            assert!(
                !b.has_unique_of_condition_kind(kind),
                "saturated-singleton boundary must return false on union has_unique_of_condition_kind({kind:?}) (2 chain matches)",
            );
        }
    }

    // ── Boundary::has_at_most_one_of_(pre|post|)condition_kind triad ─
    //
    // Two-surface parity contract with
    // `EphemeralSpec::has_at_most_one_of_condition_kind` on the "≤ 1"
    // per-kind negation arm. Boundary composes against the slice-level
    // substrate primitive `ConditionSliceExt::has_at_most_one_of_kind`
    // via delegation on each side and via the definitional negation
    // of `has_multiple_of_condition_kind` on the union chain. The
    // union-level trichotomy-union arm equivalence
    // `has_at_most_one_of_condition_kind(k) == lacks_condition_kind(k)
    // || has_unique_of_condition_kind(k)` closes the {= 0, = 1, ≥ 1,
    // ≥ 2, ≤ 1} Boolean-cardinality grid on the per-kind axis at the
    // union level.

    /// Boundary triad delegation + two-surface parity pin — sweeps
    /// every kind on every reachable arrangement of a single
    /// condition-per-side spec, asserts each per-slice arm delegates
    /// verbatim to the slice-level primitive, and asserts the union
    /// arm equals the {= 0, = 1} trichotomy-union `lacks ∨ has_unique`.
    /// Also pins the definitional-negation composition law
    /// `has_at_most_one_of_condition_kind(k) ==
    /// !has_multiple_of_condition_kind(k)` and the tetrachotomy
    /// partition (`{≤ 1, ≥ 2}` exactly one arm on every arrangement).
    /// Regression at any of these predicates or at the underlying
    /// slice-level primitive fails here.
    #[test]
    fn has_at_most_one_of_condition_kind_triad_delegates_to_slice_has_at_most_one_of_kind() {
        // Empty boundary — every arm returns true on every kind
        // (0 matches, `≤ 1`).
        let b = Boundary::default();
        for kind in ConditionKind::ALL {
            assert!(
                b.has_at_most_one_of_precondition_kind(kind),
                "empty boundary must return true on has_at_most_one_of_precondition_kind({kind:?})",
            );
            assert!(
                b.has_at_most_one_of_postcondition_kind(kind),
                "empty boundary must return true on has_at_most_one_of_postcondition_kind({kind:?})",
            );
            assert!(
                b.has_at_most_one_of_condition_kind(kind),
                "empty boundary must return true on has_at_most_one_of_condition_kind({kind:?})",
            );
            assert_eq!(
                b.has_at_most_one_of_condition_kind(kind),
                b.count_condition_kind(kind) <= 1,
                "empty has_at_most_one_of_condition_kind({kind:?}) must equal \
                 (count_condition_kind <= 1)",
            );
        }

        // Single-populated-per-side sweep — every per-side arm
        // returns `true` for every query (each side has ≤ 1 match);
        // union returns `true` iff at most one of `{pre, post}`
        // equals `query` (chain sums to 0 or 1 on disjoint,
        // 2 on shared).
        for pre_kind in ConditionKind::ALL {
            for post_kind in ConditionKind::ALL {
                let mut b = Boundary::default();
                b.preconditions.push(condition_with(pre_kind));
                b.postconditions.push(condition_with(post_kind));

                for query in ConditionKind::ALL {
                    assert_eq!(
                        b.has_at_most_one_of_precondition_kind(query),
                        b.preconditions.has_at_most_one_of_kind(query),
                        "Boundary::has_at_most_one_of_precondition_kind must delegate verbatim \
                         to preconditions.has_at_most_one_of_kind for pre={pre_kind:?} \
                         post={post_kind:?} query={query:?}",
                    );
                    assert_eq!(
                        b.has_at_most_one_of_postcondition_kind(query),
                        b.postconditions.has_at_most_one_of_kind(query),
                        "Boundary::has_at_most_one_of_postcondition_kind must delegate verbatim \
                         to postconditions.has_at_most_one_of_kind for pre={pre_kind:?} \
                         post={post_kind:?} query={query:?}",
                    );

                    // Per-side arms are always `true` — each side
                    // holds at most one condition of any given kind
                    // in this arrangement.
                    assert!(
                        b.has_at_most_one_of_precondition_kind(query),
                        "single-per-side pre arm must return true for pre={pre_kind:?} \
                         post={post_kind:?} query={query:?}",
                    );
                    assert!(
                        b.has_at_most_one_of_postcondition_kind(query),
                        "single-per-side post arm must return true for pre={pre_kind:?} \
                         post={post_kind:?} query={query:?}",
                    );

                    // Union arm — chain multiplicity is (pre_hit +
                    // post_hit); "≤ 1" fires iff the sum is 0 or 1,
                    // i.e. `!(pre_hit && post_hit)`.
                    let pre_hit = pre_kind == query;
                    let post_hit = post_kind == query;
                    let expected_union = !(pre_hit && post_hit);
                    assert_eq!(
                        b.has_at_most_one_of_condition_kind(query),
                        expected_union,
                        "Boundary::has_at_most_one_of_condition_kind({query:?}) must equal \
                         !(pre_hit && post_hit) for pre={pre_kind:?} post={post_kind:?}",
                    );

                    // Definitional negation of the many-arm peer.
                    assert_eq!(
                        b.has_at_most_one_of_condition_kind(query),
                        !b.has_multiple_of_condition_kind(query),
                        "Boundary::has_at_most_one_of_condition_kind({query:?}) drifted from \
                         !has_multiple_of_condition_kind for pre={pre_kind:?} post={post_kind:?}",
                    );

                    // Trichotomy-union arm: {= 0} ∪ {= 1} == {≤ 1}.
                    assert_eq!(
                        b.has_at_most_one_of_condition_kind(query),
                        b.lacks_condition_kind(query) || b.has_unique_of_condition_kind(query),
                        "Boundary::has_at_most_one_of_condition_kind({query:?}) drifted from \
                         (lacks || has_unique) trichotomy-union for pre={pre_kind:?} \
                         post={post_kind:?}",
                    );

                    // Composition law with count.
                    assert_eq!(
                        b.has_at_most_one_of_condition_kind(query),
                        b.count_condition_kind(query) <= 1,
                        "Boundary::has_at_most_one_of_condition_kind({query:?}) drifted from \
                         (count_condition_kind <= 1) for pre={pre_kind:?} post={post_kind:?}",
                    );

                    // {≤ 1, ≥ 2} Boolean-negation partition at the
                    // union level — EXACTLY ONE arm fires.
                    let at_most_one = b.has_at_most_one_of_condition_kind(query);
                    let multiple = b.has_multiple_of_condition_kind(query);
                    assert_ne!(
                        at_most_one, multiple,
                        "union {{≤ 1, ≥ 2}} Boolean-negation partition for query={query:?} \
                         (pre={pre_kind:?} post={post_kind:?}) must fire EXACTLY one arm",
                    );
                }
            }
        }

        // Double-populated postcondition — post arm returns false
        // on the doubled kind (≥ 2 matches, not ≤ 1), pre arm returns
        // true (0 matches, ≤ 1), union returns false (2 chain
        // matches, not ≤ 1).
        for doubled in ConditionKind::ALL {
            let mut b = Boundary::default();
            b.postconditions.push(condition_with(doubled));
            b.postconditions.push(condition_with(doubled));

            assert!(
                b.has_at_most_one_of_precondition_kind(doubled),
                "empty preconditions must return true on has_at_most_one_of_precondition_kind \
                 for doubled={doubled:?}",
            );
            assert!(
                !b.has_at_most_one_of_postcondition_kind(doubled),
                "doubled postconditions must return false on has_at_most_one_of_postcondition_kind \
                 for doubled={doubled:?}",
            );
            assert!(
                !b.has_at_most_one_of_condition_kind(doubled),
                "doubled postconditions must return false on union \
                 has_at_most_one_of_condition_kind for doubled={doubled:?}",
            );
        }
    }

    // ── ConditionSliceExt::unique_of_kind + Boundary triad ──────────
    //
    // Slice-level `Option<&Condition>` witnessing peer of the Boolean
    // `has_unique_of_kind` on the per-kind count axis. Fills the
    // Boolean → Option refinement asymmetry: distinct-axis and
    // missing-axis witness peers (`unique_distinct_kind`,
    // `unique_missing_kind`) already exist as `Option<ConditionKind>`
    // returns; this closes the third axis with an `Option<&Condition>`
    // return that additionally carries pointer identity to the
    // matched slot. Boundary triad lifts to the two-slice chain via
    // a two-step short-circuit walk over `iter_condition_kind`.

    /// EMPTY-SLICE pin — an empty `&[Condition]` returns [`None`]
    /// on every kind (0 matches, not = 1). Sweep [`ConditionKind::ALL`]
    /// so a new variant added without a matching arm surfaces at
    /// rustc's exhaustiveness gate on the ALL literal rather than
    /// as silent drift.
    #[test]
    fn condition_slice_unique_of_kind_returns_none_on_empty_slice_for_every_kind() {
        let slice: &[Condition] = &[];
        for kind in ConditionKind::ALL {
            assert!(
                slice.unique_of_kind(kind).is_none(),
                "empty slice must return None for unique_of_kind({kind:?})",
            );
            assert_eq!(
                slice.unique_of_kind(kind).is_some(),
                slice.has_unique_of_kind(kind),
                "empty slice unique_of_kind({kind:?}).is_some() must equal has_unique_of_kind",
            );
        }
    }

    /// SINGLETON pin — a slice with EXACTLY ONE match of a kind
    /// returns `Some(&c)` for THAT kind pointing at the matched
    /// slot, and [`None`] for every OTHER kind. A slice with `≥ 2`
    /// matches of a kind returns [`None`] for THAT kind (the
    /// witness collapses to no witness on the many-arm).
    #[test]
    fn condition_slice_unique_of_kind_witnesses_singleton_and_collapses_on_duplicates() {
        // Singleton sweep — one condition per kind, in isolation.
        for populated in ConditionKind::ALL {
            let slice = vec![condition_with(populated)];
            for query in ConditionKind::ALL {
                let unique = slice.unique_of_kind(query);
                if query == populated {
                    let c = unique.expect("singleton match must be Some");
                    assert_eq!(
                        c.kind, populated,
                        "unique_of_kind({query:?}) yielded &Condition with wrong kind {:?}",
                        c.kind,
                    );
                    // Pointer identity: unique_of_kind on singleton
                    // yields the exact matched slot.
                    assert!(
                        std::ptr::eq(c, &slice[0]),
                        "unique_of_kind({query:?}) singleton must point at the matched slot",
                    );
                } else {
                    assert!(
                        unique.is_none(),
                        "unique_of_kind({query:?}) must be None on singleton-{populated:?} for \
                         non-matching query",
                    );
                }
                // Boolean composition-law pin.
                assert_eq!(
                    unique.is_some(),
                    slice.has_unique_of_kind(query),
                    "unique_of_kind({query:?}).is_some() must equal has_unique_of_kind on \
                     populated={populated:?}",
                );
            }
        }

        // Doubled-kind sweep — two conditions of the same kind
        // collapse the witness to None (the many-arm).
        for doubled in ConditionKind::ALL {
            let slice = vec![condition_with(doubled), condition_with(doubled)];
            let unique = slice.unique_of_kind(doubled);
            assert!(
                unique.is_none(),
                "unique_of_kind({doubled:?}) on doubled-slice must collapse to None (≥ 2 matches)",
            );
            assert!(
                !slice.has_unique_of_kind(doubled),
                "has_unique_of_kind({doubled:?}) on doubled-slice must be false",
            );
            for query in ConditionKind::ALL {
                if query != doubled {
                    assert!(
                        slice.unique_of_kind(query).is_none(),
                        "unique_of_kind({query:?}) on doubled-{doubled:?} slice must be None for \
                         non-matching query",
                    );
                }
            }
        }
    }

    /// Boundary triad — sweeps every `(pre_kind, post_kind, query)`
    /// arrangement of a single-condition-per-side spec, asserts each
    /// per-slice arm delegates verbatim to
    /// [`ConditionSliceExt::unique_of_kind`], and pins the union arm
    /// against the chained two-step short-circuit walk. Composition
    /// laws pinned: `unique_of_condition_kind(k).is_some() ==
    /// has_unique_of_condition_kind(k)`, `unique_of_condition_kind(k)
    /// .map(|c| c.kind) == Some(k) iff has_unique_of_condition_kind`.
    #[test]
    fn unique_of_condition_kind_triad_delegates_to_slice_unique_of_kind() {
        // Empty boundary — every arm returns None on every kind.
        let b = Boundary::default();
        for kind in ConditionKind::ALL {
            assert!(
                b.unique_of_precondition_kind(kind).is_none(),
                "empty boundary must return None on unique_of_precondition_kind({kind:?})",
            );
            assert!(
                b.unique_of_postcondition_kind(kind).is_none(),
                "empty boundary must return None on unique_of_postcondition_kind({kind:?})",
            );
            assert!(
                b.unique_of_condition_kind(kind).is_none(),
                "empty boundary must return None on unique_of_condition_kind({kind:?})",
            );
        }

        // Single-populated-per-side sweep. Per-slice arms fire iff
        // that side's kind equals `query`; union arm fires iff
        // EXACTLY ONE of `{pre, post}` equals `query` (chain sums
        // to 1 on disjoint, 2 on shared).
        for pre_kind in ConditionKind::ALL {
            for post_kind in ConditionKind::ALL {
                let mut b = Boundary::default();
                b.preconditions.push(condition_with(pre_kind));
                b.postconditions.push(condition_with(post_kind));

                for query in ConditionKind::ALL {
                    // Delegation pins — per-slice arms match slice
                    // primitive on identity of the &Condition.
                    assert_eq!(
                        b.unique_of_precondition_kind(query)
                            .map(|c| c as *const Condition),
                        b.preconditions
                            .unique_of_kind(query)
                            .map(|c| c as *const Condition),
                        "Boundary::unique_of_precondition_kind must delegate verbatim to \
                         preconditions.unique_of_kind for pre={pre_kind:?} post={post_kind:?} \
                         query={query:?}",
                    );
                    assert_eq!(
                        b.unique_of_postcondition_kind(query)
                            .map(|c| c as *const Condition),
                        b.postconditions
                            .unique_of_kind(query)
                            .map(|c| c as *const Condition),
                        "Boundary::unique_of_postcondition_kind must delegate verbatim to \
                         postconditions.unique_of_kind for pre={pre_kind:?} post={post_kind:?} \
                         query={query:?}",
                    );

                    // Boolean-projection composition-law pin.
                    assert_eq!(
                        b.unique_of_condition_kind(query).is_some(),
                        b.has_unique_of_condition_kind(query),
                        "Boundary::unique_of_condition_kind({query:?}).is_some() drifted from \
                         has_unique_of_condition_kind for pre={pre_kind:?} post={post_kind:?}",
                    );
                    assert_eq!(
                        b.unique_of_condition_kind(query).map(|c| c.kind),
                        if b.has_unique_of_condition_kind(query) {
                            Some(query)
                        } else {
                            None
                        },
                        "Boundary::unique_of_condition_kind({query:?}).map(kind) must yield \
                         Some({query:?}) iff has_unique_of_condition_kind for pre={pre_kind:?} \
                         post={post_kind:?}",
                    );

                    // Union-arm shape — chain multiplicity is
                    // (pre_hit + post_hit). Some iff sum == 1 (i.e.
                    // XOR); the yielded &Condition is the
                    // precondition slot when pre_hit && !post_hit,
                    // the postcondition slot when !pre_hit && post_hit.
                    let pre_hit = pre_kind == query;
                    let post_hit = post_kind == query;
                    let unique = b.unique_of_condition_kind(query);
                    let expected_some = pre_hit ^ post_hit;
                    assert_eq!(
                        unique.is_some(),
                        expected_some,
                        "Boundary::unique_of_condition_kind({query:?}).is_some() must equal \
                         (pre_hit XOR post_hit) for pre={pre_kind:?} post={post_kind:?}",
                    );
                    if pre_hit && !post_hit {
                        assert!(
                            std::ptr::eq(unique.unwrap(), &b.preconditions[0]),
                            "union arm must point at preconditions slot when pre-only for \
                             pre={pre_kind:?} post={post_kind:?} query={query:?}",
                        );
                    } else if post_hit && !pre_hit {
                        assert!(
                            std::ptr::eq(unique.unwrap(), &b.postconditions[0]),
                            "union arm must point at postconditions slot when post-only for \
                             pre={pre_kind:?} post={post_kind:?} query={query:?}",
                        );
                    }
                }
            }
        }

        // Doubled-post sweep — union collapses to None on the
        // doubled kind (`≥ 2` chain matches, not `= 1`).
        for doubled in ConditionKind::ALL {
            let mut b = Boundary::default();
            b.postconditions.push(condition_with(doubled));
            b.postconditions.push(condition_with(doubled));
            assert!(
                b.unique_of_postcondition_kind(doubled).is_none(),
                "doubled postconditions must collapse unique_of_postcondition_kind({doubled:?}) \
                 to None",
            );
            assert!(
                b.unique_of_condition_kind(doubled).is_none(),
                "doubled postconditions must collapse union unique_of_condition_kind({doubled:?}) \
                 to None",
            );
        }
    }
}