contextgraph_types/

frame.rs

//! `ContextFrame` — the unit of exchange between a CGP host and a provider.
//! `SPEC.md` §6 fixes this exact
//! shape; frames, never blobs, carry relevance, cost, and provenance so a
//! budgeting, citing host can compose sources honestly.
//!
//! ## Frame representations (CGEP lifecycle, phase 2)
//!
//! A frame states how it carries its content through [`Representation`]:
//! `full` inlines the content (the legacy default), `compact` inlines a
//! transformed rendering alongside a resolver handle, and `reference` carries
//! no inline content at all — only a [`ContentRef`] and a
//! [`canonical_content_hash`](ContextFrame::canonical_content_hash) so a host
//! can rehydrate honestly and verifiably. `representation` absent means `full`,
//! so pre-representation providers and stored frames deserialize unchanged.

use serde::{Deserialize, Serialize};

use crate::identity::FrameId;
use crate::token::budget_tokens;
use crate::validate::{is_protocol_timestamp, is_well_formed_digest};

/// What kind of thing a frame represents.
#[derive(Debug, Clone, Copy, PartialEq, Eq, Serialize, Deserialize)]
#[serde(rename_all = "snake_case")]
pub enum FrameKind {
    Snippet,
    Symbol,
    Fact,
    Doc,
    Memory,
    Episode,
    Graph,
}

/// How a frame carries its content
/// (CGEP lifecycle build prompt, §"ContextFrame representations").
///
/// - `full`: canonical inline [`content`](ContextFrame::content) is required.
/// - `compact`: inline content, inline hash, canonical hash, a [`Transform`]
///   identity, and a [`ContentRef`] are all required.
/// - `reference`: inline content is **absent**; a [`ContentRef`] and
///   [`canonical_content_hash`](ContextFrame::canonical_content_hash) are
///   required; the inline content hash and transform are omitted.
///
/// A `full` frame omits this field on the wire ([`is_full`](Self::is_full)) so
/// legacy frames round-trip byte-for-byte.
#[derive(Debug, Clone, Copy, PartialEq, Eq, Default, Serialize, Deserialize)]
#[serde(rename_all = "snake_case")]
pub enum Representation {
    #[default]
    Full,
    Compact,
    Reference,
}

impl Representation {
    /// Whether this is the legacy default representation. A `full` frame omits
    /// the `representation` field on the wire, so a frame emitted before this
    /// field existed round-trips unchanged and `representation` absent means
    /// `full`.
    pub fn is_full(&self) -> bool {
        matches!(self, Representation::Full)
    }
}

/// The fidelity of a frame's carried content relative to its canonical source.
/// A missing value means `exact` for a legacy full frame.
#[derive(Debug, Clone, Copy, PartialEq, Eq, Serialize, Deserialize)]
#[serde(rename_all = "snake_case")]
pub enum ContentFidelity {
    Exact,
    Normalized,
    Summarized,
    Omitted,
}

/// Whether a frame's point of use requires the content inline, or accepts a
/// resolvable reference. Blocking constraints, guarded rules, ordered
/// procedures, and executable contracts require inline content at their point
/// of use; this keeps a reference choice from being confused with fidelity.
#[derive(Debug, Clone, Copy, PartialEq, Eq, Serialize, Deserialize)]
#[serde(rename_all = "snake_case")]
pub enum InlineContentRequirement {
    Required,
    ResolvableReferenceAllowed,
}

/// An opaque resolver handle for a `compact`/`reference` frame's content.
///
/// [`ContextFrame::uri`] identifies the source resource; `ContentRef::uri` is a
/// **distinct** opaque resolver handle. A `ContentRef` also names the exact
/// [`provider_id`](Self::provider_id) that returned it, so a fan-out host routes
/// resolution back to that provider.
#[derive(Debug, Clone, PartialEq, Eq, Serialize, Deserialize)]
pub struct ContentRef {
    /// The exact provider that returned this frame; a fan-out host routes
    /// `context/resolve` back to it.
    pub provider_id: String,
    /// Opaque resolver handle, distinct from [`ContextFrame::uri`].
    pub uri: String,
    /// When the handle stops resolving. Absent ⇒ no declared expiry.
    #[serde(default, skip_serializing_if = "Option::is_none")]
    pub expires_at: Option<String>,
}

/// The transformation identity a `compact` frame applies to its source to
/// produce the inline rendering, so a consumer knows what it is reading.
#[derive(Debug, Clone, PartialEq, Eq, Serialize, Deserialize)]
pub struct Transform {
    /// e.g. `extractive_summary`, `truncation`.
    pub method: String,
    /// e.g. `provider_default`, or a named implementation.
    pub implementation: String,
    pub version: String,
}

/// One link in a frame's provenance chain, ordered closest-to-source first.
#[derive(Debug, Clone, PartialEq, Serialize, Deserialize)]
pub struct Provenance {
    /// e.g. "file", "derivation", "episode".
    #[serde(rename = "type")]
    pub kind: String,
    #[serde(default, skip_serializing_if = "Option::is_none")]
    pub uri: Option<String>,
    #[serde(default, skip_serializing_if = "Option::is_none")]
    pub range: Option<String>,
    #[serde(default, skip_serializing_if = "Option::is_none")]
    pub digest: Option<String>,
    #[serde(default, skip_serializing_if = "Option::is_none")]
    pub method: Option<String>,
    #[serde(default, skip_serializing_if = "Option::is_none")]
    pub by: Option<String>,
}

impl Provenance {
    /// Whether this link addresses bytes a host could independently re-read.
    pub fn is_file_provenance(&self) -> bool {
        self.kind == "file"
    }

    /// Whether the digest, if present, matches the grammar in `SPEC.md` §F5.
    ///
    /// Absent counts as *not* well-formed: for file provenance the digest is
    /// what makes tamper-detection possible at all, and treating "no digest"
    /// as acceptable is how the guarantee stayed decorative for so long.
    pub fn has_well_formed_digest(&self) -> bool {
        self.digest.as_deref().is_some_and(is_well_formed_digest)
    }
}

/// The recommended relation vocabulary (`SPEC.md` §Graph).
///
/// `Relation.rel` is an **open** vocabulary — a provider may emit any string,
/// and a host must not reject an unknown one. These constants exist so that
/// independent providers converge on the same spelling for the same edge
/// instead of each inventing `calls` / `call` / `code.call`. Using them is
/// SHOULD-level, not MUST.
///
/// Namespacing is the part that matters: a provider-specific edge belongs
/// under its own prefix (`myindex.owns`), which keeps the shared namespace
/// meaningful and makes a future registry possible.
pub mod rel {
    /// The subject calls the target.
    pub const CODE_CALLS: &str = "code.calls";
    /// The subject imports the target.
    pub const CODE_IMPORTS: &str = "code.imports";
    /// The subject defines the target.
    pub const CODE_DEFINES: &str = "code.defines";
    /// The subject references the target without calling it.
    pub const CODE_REFERENCES: &str = "code.references";
    /// The subject documents the target.
    pub const DOC_DOCUMENTS: &str = "doc.documents";
    /// The subject episode follows the target episode in time.
    pub const EPISODE_FOLLOWS: &str = "episode.follows";

    /// Every relation this revision names. A registry, not a restriction.
    pub const RECOMMENDED: &[&str] = &[
        CODE_CALLS,
        CODE_IMPORTS,
        CODE_DEFINES,
        CODE_REFERENCES,
        DOC_DOCUMENTS,
        EPISODE_FOLLOWS,
    ];
}

/// A graph relation a frame participates in, surfaced with a human label —
/// raw ids are never the primary identifier (`SPEC.md` §G1).
#[derive(Debug, Clone, PartialEq, Serialize, Deserialize)]
pub struct Relation {
    /// The edge label. See [`rel`] for the recommended vocabulary; unknown
    /// values are valid and **MUST NOT** be rejected by a host.
    pub rel: String,
    pub target_uri: String,
    #[serde(default, skip_serializing_if = "Option::is_none")]
    pub display_name: Option<String>,
}

impl Relation {
    /// Whether this edge can be surfaced to a human by name.
    ///
    /// The "never a raw id" rule has been documented since the protocol's first
    /// draft and was checked by nothing; `SPEC.md` §G1 now makes it a
    /// conformance requirement for graph-capable providers, and this is the
    /// predicate behind it.
    pub fn has_display_name(&self) -> bool {
        self.display_name
            .as_deref()
            .is_some_and(|name| !name.trim().is_empty())
    }

    /// Whether this edge points somewhere (`SPEC.md` §G2).
    ///
    /// `target_uri` is a required field, so serde guarantees it is *present* —
    /// but `""` deserializes happily, and an edge to nowhere is not an edge.
    /// The schema has carried `minLength: 1` here from the start; §G2 claimed
    /// `frame-validity` verified it and no code did, which is the
    /// self-attestation §11.1 exists to rule out.
    pub fn has_target_uri(&self) -> bool {
        !self.target_uri.trim().is_empty()
    }

    /// Whether `rel` uses the recommended vocabulary. Advisory only — a `false`
    /// here is a hint for a provider author, never a conformance failure.
    pub fn uses_recommended_vocabulary(&self) -> bool {
        rel::RECOMMENDED.contains(&self.rel.as_str())
    }
}

/// The optional embedding carried by a frame. The vector itself is
/// elidable — a host may want the fingerprint without the payload.
#[derive(Debug, Clone, PartialEq, Serialize, Deserialize)]
pub struct FrameEmbedding {
    pub fingerprint: String,
    #[serde(default, skip_serializing_if = "Option::is_none")]
    pub vector: Option<Vec<f32>>,
}

/// One context frame returned from `context/query`.
#[derive(Debug, Clone, PartialEq, Serialize, Deserialize)]
pub struct ContextFrame {
    /// Provider-scoped, stable for dedup across queries.
    pub id: String,
    pub kind: FrameKind,
    /// Human label — never a bare uuid.
    pub title: String,
    /// Text the host may quote into a prompt. Untrusted data: a conforming
    /// host delimits this as quoted material, never as instructions.
    ///
    /// Present for `full`/`compact` frames; **absent** for `reference` frames,
    /// which carry only a [`content_ref`](Self::content_ref). A reference is
    /// never encoded as `content: ""` — the field is omitted entirely.
    #[serde(default, skip_serializing_if = "Option::is_none")]
    pub content: Option<String>,
    /// The provider-declared digest of this frame's **inline** content bytes —
    /// the third component of its stable [`FrameId`](crate::FrameId) identity,
    /// opaque to the protocol (e.g. `sha256:<hex>`). This is the spec's
    /// `content_hash` (SHA-256 over the exact inline UTF-8 content) under its
    /// established name; see [`canonical_content_hash`](Self::canonical_content_hash)
    /// for the full-source hash. Absent ⇒ the frame is not verifiable and a
    /// host re-queries it rather than reusing it unchecked
    /// (`docs/context-reuse.md` §1, §4). A `reference` frame omits it.
    #[serde(default, skip_serializing_if = "Option::is_none")]
    pub content_digest: Option<String>,
    #[serde(default, skip_serializing_if = "Option::is_none")]
    pub uri: Option<String>,
    /// How this frame carries its content. Absent ⇒ [`Representation::Full`],
    /// so legacy frames deserialize unchanged and full frames omit the field.
    #[serde(default, skip_serializing_if = "Representation::is_full")]
    pub representation: Representation,
    /// Fidelity of the carried content relative to the source. Absent ⇒ `exact`
    /// for a legacy full frame.
    #[serde(default, skip_serializing_if = "Option::is_none")]
    pub content_fidelity: Option<ContentFidelity>,
    /// SHA-256 over the **complete source content** bytes (distinct from the
    /// inline [`content_digest`](Self::content_digest)). Required for
    /// `compact`/`reference` frames so a resolved rehydration is verifiable.
    #[serde(default, skip_serializing_if = "Option::is_none")]
    pub canonical_content_hash: Option<String>,
    /// The opaque resolver handle for a `compact`/`reference` frame's content.
    #[serde(default, skip_serializing_if = "Option::is_none")]
    pub content_ref: Option<ContentRef>,
    /// The transformation a `compact` frame applied to its source. Omitted for
    /// `full`/`reference` frames.
    #[serde(default, skip_serializing_if = "Option::is_none")]
    pub transform: Option<Transform>,
    /// The lowest content fidelity acceptable at this frame's point of use.
    #[serde(default, skip_serializing_if = "Option::is_none")]
    pub minimum_content_fidelity: Option<ContentFidelity>,
    /// Whether this frame's point of use requires inline content.
    #[serde(default, skip_serializing_if = "Option::is_none")]
    pub inline_content_requirement: Option<InlineContentRequirement>,
    /// Provider-normalized relevance in `[0, 1]`.
    pub score: f32,
    /// Honest, conformance-audited token cost of the **inline** rendering.
    pub token_cost: u32,
    /// Token cost of the complete canonical source content, when the provider
    /// declares it. If present, [`tokenizer_ref`](Self::tokenizer_ref) SHOULD
    /// name the tokenizer it was measured with. Hosts compute model-specific
    /// costs when providers omit it.
    #[serde(default, skip_serializing_if = "Option::is_none")]
    pub canonical_token_cost: Option<u32>,
    /// Identifies the tokenizer that produced the declared costs
    /// (e.g. `openai:o200k_base`).
    #[serde(default, skip_serializing_if = "Option::is_none")]
    pub tokenizer_ref: Option<String>,
    #[serde(default, skip_serializing_if = "Option::is_none")]
    pub valid_from: Option<String>,
    #[serde(default, skip_serializing_if = "Option::is_none")]
    pub valid_to: Option<String>,
    #[serde(default, skip_serializing_if = "Option::is_none")]
    pub recorded_at: Option<String>,
    #[serde(default, skip_serializing_if = "Vec::is_empty")]
    pub provenance: Vec<Provenance>,
    #[serde(default, skip_serializing_if = "Option::is_none")]
    pub citation_label: Option<String>,
    #[serde(default, skip_serializing_if = "Option::is_none")]
    pub embedding: Option<FrameEmbedding>,
    #[serde(default, skip_serializing_if = "Vec::is_empty")]
    pub relations: Vec<Relation>,
}

impl ContextFrame {
    /// A `full`-representation frame carrying inline `content` — the shape every
    /// legacy provider emits. The representation/cost/resolver fields default to
    /// absent, so a call site need only supply the core, then set extras as
    /// needed (the build prompt asks for constructors to reduce source
    /// breakage).
    pub fn full(
        id: impl Into<String>,
        kind: FrameKind,
        title: impl Into<String>,
        content: impl Into<String>,
        score: f32,
        token_cost: u32,
    ) -> Self {
        Self {
            id: id.into(),
            kind,
            title: title.into(),
            content: Some(content.into()),
            content_digest: None,
            uri: None,
            representation: Representation::Full,
            content_fidelity: None,
            canonical_content_hash: None,
            content_ref: None,
            transform: None,
            minimum_content_fidelity: None,
            inline_content_requirement: None,
            score,
            token_cost,
            canonical_token_cost: None,
            tokenizer_ref: None,
            valid_from: None,
            valid_to: None,
            recorded_at: None,
            provenance: Vec::new(),
            citation_label: None,
            embedding: None,
            relations: Vec::new(),
        }
    }

    /// A `reference`-representation frame: no inline content, only a resolver
    /// handle and the canonical source hash for honest, verifiable rehydration.
    /// `token_cost` is the inline cost (0 — nothing is inlined).
    pub fn reference(
        id: impl Into<String>,
        kind: FrameKind,
        title: impl Into<String>,
        content_ref: ContentRef,
        canonical_content_hash: impl Into<String>,
        score: f32,
    ) -> Self {
        Self {
            representation: Representation::Reference,
            content: None,
            content_ref: Some(content_ref),
            canonical_content_hash: Some(canonical_content_hash.into()),
            ..Self::full(id, kind, title, String::new(), score, 0)
        }
        // `..full(..)` seeds every other field; the overrides above make this a
        // structurally honest reference (content absent, content_digest None,
        // transform None) that satisfies `representation_invariants`.
    }

    /// Score must be normalized into `[0, 1]` per the protocol contract.
    /// Conformance suites assert this; providers should self-check too.
    pub fn has_valid_score(&self) -> bool {
        (0.0..=1.0).contains(&self.score)
    }

    /// The frame's stable identity under the given provider: `(provider id,
    /// frame id, content digest)`. The digest is carried through from
    /// [`content_digest`](Self::content_digest), so a frame without one yields
    /// an unverifiable identity (`docs/context-reuse.md` §1).
    pub fn identity(&self, provider_id: impl Into<String>) -> FrameId {
        FrameId::new(provider_id, self.id.clone(), self.content_digest.clone())
    }

    /// The token cost this frame's **inline** content is *required* to declare
    /// (`SPEC.md` §B3) — see [`budget_tokens`](crate::budget_tokens). A
    /// `reference` frame carries no inline content, so its expected cost is 0.
    ///
    /// Distinct from the [`canonical_token_cost`](Self::canonical_token_cost)
    /// *field*, which is the provider-declared cost of the full source content.
    pub fn expected_inline_token_cost(&self) -> u32 {
        budget_tokens(self.content.as_deref().unwrap_or(""))
    }

    /// Whether `token_cost` matches the canonical count for this frame's
    /// content.
    ///
    /// This is the check that turned budget honesty from arithmetic into
    /// truth: previously a provider could declare `token_cost: 1` on a
    /// ten-thousand-token frame and pass every check in the suite.
    pub fn declares_honest_token_cost(&self) -> bool {
        self.token_cost == self.expected_inline_token_cost()
    }

    /// The names of any temporal fields that are not in the protocol's
    /// timestamp profile (`SPEC.md` §F4).
    ///
    /// Returns the field *names* rather than a bare bool so a conformance
    /// failure can say which field was wrong — an evidence string reading
    /// "valid_from" is actionable in a way that "temporal validation failed"
    /// is not.
    pub fn invalid_temporal_fields(&self) -> Vec<&'static str> {
        [
            ("valid_from", self.valid_from.as_deref()),
            ("valid_to", self.valid_to.as_deref()),
            ("recorded_at", self.recorded_at.as_deref()),
        ]
        .into_iter()
        .filter(|(_, value)| value.is_some_and(|v| !is_protocol_timestamp(v)))
        .map(|(name, _)| name)
        .collect()
    }

    /// Whether every temporal field present on this frame is well-formed.
    pub fn has_valid_temporal_fields(&self) -> bool {
        self.invalid_temporal_fields().is_empty()
    }

    /// Provenance entries that address a file but carry a malformed or missing
    /// digest (`SPEC.md` §F5).
    ///
    /// File provenance is held to a stricter standard than other kinds because
    /// it is the one the host can independently verify: the bytes are on disk.
    /// A `derivation` or `episode` link has no addressable bytes, so requiring
    /// a digest of it would be theatre.
    pub fn provenance_with_unusable_digests(&self) -> Vec<usize> {
        self.provenance
            .iter()
            .enumerate()
            .filter(|(_, p)| p.is_file_provenance() && !p.has_well_formed_digest())
            .map(|(index, _)| index)
            .collect()
    }

    /// Whether this frame's own `content_digest`, if it carries one, is in the
    /// protocol's digest form (`SPEC.md` §D1).
    ///
    /// Absent is fine — §D1 binds the digest only "when present". What is not
    /// fine is a *present* digest that no host can compare against, which is
    /// what `sha256:abc` is. §D1 named `frame-validity` as its verifier while
    /// nothing read this field: the digest that anchors deterministic
    /// composition, usage reports, and `context/verify` was the one digest in
    /// the protocol that went unchecked, and §F5 held provenance to a stricter
    /// standard than the frame's own identity.
    pub fn has_usable_content_digest(&self) -> bool {
        self.content_digest
            .as_deref()
            .is_none_or(is_well_formed_digest)
    }

    /// Whether this frame's fields satisfy the invariants of its declared
    /// [`representation`](Self::representation). Providers emit conforming
    /// frames; hosts reject a frame that lies about its shape (e.g. a
    /// `reference` carrying inline content, or a `compact` missing its
    /// canonical hash). The `Err` string names the exact violation.
    pub fn representation_invariants(&self) -> Result<(), String> {
        match self.representation {
            Representation::Full => {
                if self.content.is_none() {
                    return Err("full frame requires inline content".into());
                }
            }
            Representation::Compact => {
                if self.content.is_none() {
                    return Err("compact frame requires inline content".into());
                }
                if self.content_digest.is_none() {
                    return Err(
                        "compact frame requires an inline content hash (content_digest)".into(),
                    );
                }
                if self.canonical_content_hash.is_none() {
                    return Err("compact frame requires canonical_content_hash".into());
                }
                if self.transform.is_none() {
                    return Err("compact frame requires a transform identity".into());
                }
                if self.content_ref.is_none() {
                    return Err("compact frame requires content_ref".into());
                }
            }
            Representation::Reference => {
                // "Never encode a reference as content: \"\"" — any inline
                // content, empty or not, is a violation.
                if self.content.is_some() {
                    return Err("reference frame must not carry inline content".into());
                }
                if self.content_ref.is_none() {
                    return Err("reference frame requires content_ref".into());
                }
                if self.canonical_content_hash.is_none() {
                    return Err("reference frame requires canonical_content_hash".into());
                }
                if self.content_digest.is_some() {
                    return Err(
                        "reference frame must omit the inline content hash (content_digest)".into(),
                    );
                }
                if self.transform.is_some() {
                    return Err("reference frame must omit transform".into());
                }
            }
        }
        Ok(())
    }
}

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

    fn sample_frame() -> ContextFrame {
        let mut frame = ContextFrame::full(
            "frm_1",
            FrameKind::Snippet,
            "workspace.ts L120-160",
            "export interface Workspace { ... }",
            0.83,
            412,
        );
        frame.content_digest = Some("sha256:abc".into());
        frame.uri = Some("file:///repo/workspace.ts".into());
        frame.recorded_at = Some("2026-07-10T00:00:00Z".into());
        frame.provenance = vec![Provenance {
            kind: "file".into(),
            uri: Some("file:///repo/workspace.ts".into()),
            range: Some("L120-160".into()),
            digest: Some("sha256:abc".into()),
            method: None,
            by: None,
        }];
        frame.citation_label = Some("workspace.ts L120-160".into());
        frame
    }

    #[test]
    fn context_frame_roundtrips_through_json() {
        let frame = sample_frame();
        let json = serde_json::to_string(&frame).unwrap();
        let back: ContextFrame = serde_json::from_str(&json).unwrap();
        assert_eq!(back, frame);
    }

    #[test]
    fn score_out_of_range_fails_the_conformance_check() {
        let mut frame = sample_frame();
        assert!(frame.has_valid_score());
        frame.score = 1.5;
        assert!(!frame.has_valid_score());
    }

    #[test]
    fn an_honest_frame_declares_the_canonical_cost_of_its_content() {
        let mut frame = sample_frame();
        frame.content = Some("abcd".repeat(10)); // 40 bytes -> 10 budget tokens
        frame.token_cost = 10;
        assert!(frame.declares_honest_token_cost());
        assert_eq!(frame.expected_inline_token_cost(), 10);
    }

    #[test]
    fn the_budget_lie_that_used_to_pass_every_check_is_now_caught() {
        // Issue #8's headline case: a provider reporting `token_cost: 1` on a
        // huge frame satisfied `sum(token_cost) <= max_tokens` perfectly.
        let mut frame = sample_frame();
        frame.content = Some("x".repeat(10_000));
        frame.token_cost = 1;
        assert!(!frame.declares_honest_token_cost());
        assert_eq!(frame.expected_inline_token_cost(), 2_500);
    }

    #[test]
    fn over_reporting_cost_is_a_lie_too_even_though_it_is_self_harming() {
        // Exact equality, not an upper bound: an inflated cost would let a
        // provider crowd honest peers out of a shared budget.
        let mut frame = sample_frame();
        frame.content = Some("abcd".into());
        frame.token_cost = 500;
        assert!(!frame.declares_honest_token_cost());
    }

    #[test]
    fn malformed_temporal_fields_are_reported_by_name() {
        let mut frame = sample_frame();
        frame.valid_from = Some("last tuesday".into());
        frame.valid_to = Some("2026-08-01T00:00:00Z".into());
        frame.recorded_at = Some("2026-07-10".into());

        // The names are what make a conformance failure actionable.
        assert_eq!(
            frame.invalid_temporal_fields(),
            vec!["valid_from", "recorded_at"]
        );
        assert!(!frame.has_valid_temporal_fields());
    }

    #[test]
    fn absent_temporal_fields_are_valid_because_they_are_optional() {
        let mut frame = sample_frame();
        frame.valid_from = None;
        frame.valid_to = None;
        frame.recorded_at = None;
        assert!(frame.has_valid_temporal_fields());
    }

    #[test]
    fn file_provenance_without_a_usable_digest_is_flagged_by_index() {
        let mut frame = sample_frame();
        // `sha256:abc` is the placeholder the pre-spec fixtures used.
        assert_eq!(frame.provenance_with_unusable_digests(), vec![0]);

        frame.provenance[0].digest = Some(format!("sha256:{}", "a".repeat(64)));
        assert!(frame.provenance_with_unusable_digests().is_empty());
    }

    #[test]
    fn non_file_provenance_is_not_required_to_carry_a_digest() {
        // A derivation has no addressable bytes to digest, so demanding one
        // would be theatre rather than integrity.
        let mut frame = sample_frame();
        frame.provenance = vec![Provenance {
            kind: "derivation".into(),
            uri: None,
            range: None,
            digest: None,
            method: Some("summarized".into()),
            by: Some("contextgraph-docs".into()),
        }];
        assert!(frame.provenance_with_unusable_digests().is_empty());
    }

    #[test]
    fn a_graph_edge_must_be_citable_by_a_human_label() {
        let edge = Relation {
            rel: rel::CODE_CALLS.into(),
            target_uri: "file:///repo/src/net.rs#retry".into(),
            display_name: Some("net::retry".into()),
        };
        assert!(edge.has_display_name());
        assert!(edge.uses_recommended_vocabulary());

        // A raw id with no label is exactly what the "never a bare uuid" rule
        // forbids, and nothing checked it before.
        let unlabeled = Relation {
            rel: "myindex.owns".into(),
            target_uri: "file:///repo/src/net.rs".into(),
            display_name: None,
        };
        assert!(!unlabeled.has_display_name());
        // ...but an out-of-vocabulary `rel` is perfectly legal.
        assert!(!unlabeled.uses_recommended_vocabulary());
    }

    #[test]
    fn a_whitespace_only_display_name_does_not_count_as_a_label() {
        let edge = Relation {
            rel: rel::DOC_DOCUMENTS.into(),
            target_uri: "file:///docs/net.md".into(),
            display_name: Some("   ".into()),
        };
        assert!(!edge.has_display_name());
    }

    #[test]
    fn a_present_content_digest_must_be_usable_but_an_absent_one_is_fine() {
        // §D1 binds the digest only "when present": a frame that carries none
        // is conformant, a frame that carries `sha256:abc` is not.
        let mut frame = sample_frame();
        frame.content_digest = None;
        assert!(frame.has_usable_content_digest(), "absent is permitted");

        frame.content_digest = Some(format!("sha256:{}", "a".repeat(64)));
        assert!(frame.has_usable_content_digest());

        for malformed in ["sha256:abc", &format!("sha256:{}", "A".repeat(64))] {
            frame.content_digest = Some(malformed.to_string());
            assert!(
                !frame.has_usable_content_digest(),
                "{malformed} is not a comparable digest"
            );
        }
    }

    #[test]
    fn an_edge_pointing_nowhere_does_not_satisfy_g2() {
        // §G2 says `target_uri` MUST be a non-empty URI and claimed
        // `frame-validity` checked it; nothing read the field at all. serde
        // guarantees presence (it is not an Option), so the reachable breach is
        // the empty — or whitespace-only — string, which the schema's
        // `minLength: 1` rejects and the Rust side silently accepted.
        let labelled_but_dangling = Relation {
            rel: rel::DOC_DOCUMENTS.into(),
            target_uri: String::new(),
            display_name: Some("Net docs".into()),
        };
        assert!(labelled_but_dangling.has_display_name(), "§G1 is satisfied");
        assert!(!labelled_but_dangling.has_target_uri(), "but §G2 is not");

        let whitespace = Relation {
            target_uri: "   ".into(),
            ..labelled_but_dangling.clone()
        };
        assert!(!whitespace.has_target_uri());

        let real = Relation {
            target_uri: "file:///docs/net.md".into(),
            ..labelled_but_dangling
        };
        assert!(real.has_target_uri());
    }

    #[test]
    fn optional_fields_are_omitted_when_absent() {
        let frame = sample_frame();
        let mut minimal = frame.clone();
        minimal.uri = None;
        minimal.valid_from = None;
        minimal.content_digest = None;
        minimal.provenance.clear();
        let json = serde_json::to_string(&minimal).unwrap();
        assert!(!json.contains("\"uri\""));
        assert!(!json.contains("\"provenance\""));
        assert!(!json.contains("\"content_digest\""));
    }

    #[test]
    fn full_frame_omits_representation_on_the_wire() {
        // A full frame keeps the legacy wire shape: `representation` is absent,
        // so pre-representation consumers see no new field.
        let frame = sample_frame();
        assert_eq!(frame.representation, Representation::Full);
        let json = serde_json::to_string(&frame).unwrap();
        assert!(
            !json.contains("representation"),
            "full frames must omit the representation field: {json}"
        );
        assert!(frame.representation_invariants().is_ok());
    }

    #[test]
    fn reference_frame_omits_content_and_round_trips_its_handle() {
        let frame = ContextFrame::reference(
            "frm_ref_1",
            FrameKind::Doc,
            "Deployment runbook",
            ContentRef {
                provider_id: "provider_example".into(),
                uri: "context://provider_example/records/doc_runbook_v1".into(),
                expires_at: None,
            },
            "sha256:9f86d081884c7d659a2feaa0c55ad015a3bf4f1b2b0b822cd15d6c15b0f00a08",
            0.9,
        );
        frame
            .representation_invariants()
            .expect("constructed reference frame must be structurally honest");

        let json = serde_json::to_string(&frame).unwrap();
        assert!(
            !json.contains("\"content\""),
            "a reference frame must not carry inline content: {json}"
        );
        assert!(json.contains("\"representation\":\"reference\""));

        let back: ContextFrame = serde_json::from_str(&json).unwrap();
        assert_eq!(back, frame);
        assert_eq!(back.representation, Representation::Reference);
        assert_eq!(
            back.content_ref.as_ref().unwrap().provider_id,
            "provider_example"
        );
    }

    #[test]
    fn a_reference_with_inline_content_violates_its_invariants() {
        let mut frame = ContextFrame::reference(
            "frm_ref_2",
            FrameKind::Doc,
            "Runbook",
            ContentRef {
                provider_id: "p".into(),
                uri: "context://p/r".into(),
                expires_at: None,
            },
            "sha256:aa",
            0.5,
        );
        // Even an empty string is a lie for a reference.
        frame.content = Some(String::new());
        assert!(frame.representation_invariants().is_err());
    }

    #[test]
    fn compact_frame_requires_its_full_metadata_set() {
        let mut frame = sample_frame();
        frame.representation = Representation::Compact;
        // full()-seeded frame lacks the compact metadata → invalid.
        assert!(frame.representation_invariants().is_err());

        frame.content_digest = Some("sha256:inline".into());
        frame.canonical_content_hash = Some("sha256:canonical".into());
        frame.transform = Some(Transform {
            method: "extractive_summary".into(),
            implementation: "provider_default".into(),
            version: "1".into(),
        });
        frame.content_ref = Some(ContentRef {
            provider_id: "provider_example".into(),
            uri: "context://provider_example/records/x".into(),
            expires_at: None,
        });
        frame.content = Some("summary…".into());
        assert!(frame.representation_invariants().is_ok());
    }
}