tix/

workflow.rs

//! The single owner of category resolution, completion, and transition legality.
//!
//! **Filesystem-free on purpose.** Nothing here reads or writes an issue file, and
//! nothing here takes a `Store`. The module returns the accepted transition and
//! the decision to append; WP03's storage seam performs the write. That is what
//! lets the CLI, the TUI, MCP, sync and every analytic share one implementation
//! instead of five that agree today (contract §2).
//!
//! **`blocked` here is a workflow column position, not blocked *state*.** The
//! derived blocked state — an open inbound `blocks` edge — is a graph fact owned
//! by issue 169's Mission and lives in `relationships.rs`. The two are different
//! things and the contract names conflating them a rejected alternative
//! (`category-vocabulary.md` §6).
//!
//! **Resolution is built once**, at config load, and is not rebuilt per issue or
//! per surface. The per-issue path is a single hash lookup, which is what holds
//! NFR-001 for a 10,000-issue sweep (contract §7). Rebuilding it per issue is the
//! failure mode this design exists to prevent, and `resolution` is built from a
//! board rather than from an issue so that it cannot be.

use std::collections::HashMap;
use std::fmt;

use crate::config::{
    BoardConfiguration, CATEGORY_KEYS, COMPLETE_CATEGORY, Config, SAFE_DEFAULT_CATEGORY,
};
use crate::model::Issue;

/// A category in the fixed global vocabulary (C-002).
///
/// The vocabulary is global and closed: a board maps its columns *into* these
/// keys and does not define its own. The spelling comes from WP01's
/// [`CATEGORY_KEYS`] rather than from string literals here, so the config
/// validator and this service cannot disagree about what a category is.
#[derive(Debug, Clone, Copy, PartialEq, Eq, PartialOrd, Ord, Hash)]
pub enum WorkflowCategory {
    Backlog,
    Unstarted,
    Active,
    Blocked,
    Completed,
    Canceled,
}

impl WorkflowCategory {
    /// Every category, in the vocabulary's order.
    pub const ALL: [WorkflowCategory; 6] = [
        WorkflowCategory::Backlog,
        WorkflowCategory::Unstarted,
        WorkflowCategory::Active,
        WorkflowCategory::Blocked,
        WorkflowCategory::Completed,
        WorkflowCategory::Canceled,
    ];

    /// The canonical spelling used in config and in output.
    pub fn key(self) -> &'static str {
        match self {
            WorkflowCategory::Backlog => "backlog",
            WorkflowCategory::Unstarted => "unstarted",
            WorkflowCategory::Active => "active",
            WorkflowCategory::Blocked => "blocked",
            WorkflowCategory::Completed => "completed",
            WorkflowCategory::Canceled => "canceled",
        }
    }

    /// Parse a key, or `None` for anything outside the vocabulary.
    ///
    /// The `Option` is load-bearing: an unknown key is an error
    /// (`unknown_category`), never a coerced default. A `from_key` that fell back
    /// to `unstarted` would turn a typo in a config into a board where a column
    /// silently means something else.
    pub fn from_key(key: &str) -> Option<Self> {
        CATEGORY_KEYS
            .iter()
            .position(|k| *k == key)
            .map(|i| Self::ALL[i])
    }

    /// Whether this category ends the workflow.
    ///
    /// True for `completed` **and** `canceled` — which is exactly why completion is
    /// not `is_terminal()`. A category can end the work without the work having
    /// been completed.
    pub fn is_terminal(self) -> bool {
        matches!(
            self,
            WorkflowCategory::Completed | WorkflowCategory::Canceled
        )
    }

    /// Whether this category means the work is done.
    ///
    /// The **only** definition of completion in the crate. `canceled` is terminal
    /// and not complete.
    pub fn is_complete(self) -> bool {
        self.key() == COMPLETE_CATEGORY
    }

    /// Display text. Presentation only; never consulted for a decision.
    pub fn label(self) -> &'static str {
        match self {
            WorkflowCategory::Backlog => "Backlog",
            WorkflowCategory::Unstarted => "Not started",
            WorkflowCategory::Active => "In progress",
            WorkflowCategory::Blocked => "Blocked",
            WorkflowCategory::Completed => "Done",
            WorkflowCategory::Canceled => "Canceled",
        }
    }

    /// A presentation hint for the TUI, or `None` where there is nothing to say.
    ///
    /// **Inert.** It never affects resolution, policy, or reporting — a category
    /// with a colour and a category without one resolve identically. A colour that
    /// changed a decision would make the board's appearance load-bearing.
    pub fn color_hint(self) -> Option<ColorHint> {
        match self {
            WorkflowCategory::Backlog => Some(ColorHint::Dim),
            WorkflowCategory::Active => Some(ColorHint::Accent),
            WorkflowCategory::Blocked => Some(ColorHint::Warn),
            WorkflowCategory::Completed => Some(ColorHint::Ok),
            WorkflowCategory::Canceled => Some(ColorHint::Muted),
            // Deliberately `None`: "not started" is the absence of work, and
            // giving it a colour would make an untouched card look like a
            // deliberate state.
            WorkflowCategory::Unstarted => None,
        }
    }
}

/// A presentation hint. See [`WorkflowCategory::color_hint`].
#[derive(Debug, Clone, Copy, PartialEq, Eq)]
pub enum ColorHint {
    Dim,
    Accent,
    Warn,
    Ok,
    Muted,
}

/// The built once-per-load derivation from column name to category
/// (`data-model.md` §3).
#[derive(Debug, Clone, PartialEq, Eq)]
pub struct CategoryResolution {
    /// Every configured column and its category. Looked up, never scanned.
    by_column: HashMap<String, WorkflowCategory>,
    /// Every configured column, in **board order**.
    ///
    /// WP03. `by_column` is a `HashMap`, so iterating it yields keys in an
    /// unspecified order. That was harmless while `columns()` had no callers, but
    /// [`Self::columns`] already *documented* board order while being unable to
    /// deliver it, and WP03's widened `unknown_column` message prints the valid
    /// columns to the user. A `HashMap` order would make that list differ between
    /// two runs over the same config — an unstable error message, and a test that
    /// passes or fails on the allocator's whim.
    ///
    /// A second copy of the key set, not a replacement: lookups stay `O(1)` on
    /// `by_column`, and this vector exists only to make iteration deterministic.
    order: Vec<String>,
    /// Configured columns that resolved by the safe default rather than by an
    /// explicit mapping, in board order.
    ///
    /// Recorded so a surface can report `unmapped_column_default` "where ambiguity
    /// matters". A column silently defaulting is the thing the contract is most
    /// careful about, and it cannot be reported from the map alone.
    pub unmapped: Vec<String>,
    /// Whether any column relied on the default. Lets a caller skip the
    /// diagnostic entirely on a fully-mapped board.
    pub default_applied: bool,
    /// Whether the board **declared** a `category_map`, as opposed to resolving
    /// every column through the safe default.
    ///
    /// WP03. This is the signal that separates a board whose author described its
    /// categories from one that never did, and it is what gates the **terminal
    /// lock**. Without it, WP01's legacy reconciliation (`done_column` resolves to
    /// `completed` so completion detection works, FR-003) would silently hand every
    /// existing repository a transition policy it never configured: moving an issue
    /// back out of `done` would start failing on every board in the wild, and on the
    /// TUI there is no flag or key to override it with for two more work packages.
    ///
    /// Deliberately distinct from [`Self::default_applied`]: a board may declare a
    /// `category_map` and still leave some columns to the default, so
    /// `default_applied` is "some column is unmapped" while this is "a map was
    /// written at all". The lock is about intent, and intent is expressed by the
    /// presence of the section.
    ///
    /// Note the consequence, since it is a real one: a legacy board gets the
    /// **completion** definition and the **commit-clearing** rule, but not the
    /// terminal lock. Those are different things — completion answers "is this
    /// done?", the lock answers "may this move?" — and the contract treats them in
    /// different sections for that reason.
    pub explicit_policy: bool,
    /// The board's name, for diagnostics.
    pub board: String,
}

impl CategoryResolution {
    /// The category `column` resolves to, or `None` for a column this board does
    /// not configure.
    ///
    /// A hash lookup. A caller that needs to distinguish "not configured" from
    /// "configured but defaulted" uses [`Self::unmapped`].
    pub fn resolve(&self, column: &str) -> Option<WorkflowCategory> {
        self.by_column.get(column).copied()
    }

    /// Every column this board configures, in board order.
    ///
    /// Reads [`Self::order`], not `by_column`, so the sequence is the board's own
    /// declaration order and is the same on every run (see the field's note).
    pub fn columns(&self) -> impl Iterator<Item = &str> {
        self.order.iter().map(String::as_str)
    }

    /// The board's columns joined for a message, in board order.
    ///
    /// WP03. A `unknown_column` refusal is the one diagnostic a user reads to work
    /// out what to type instead, so it must list the valid columns. Rendering that
    /// list in one place keeps every `unknown_column` message agreeing on it.
    pub fn column_list(&self) -> String {
        self.order.join(", ")
    }

    /// Whether any column resolves to `completed`.
    pub fn has_completion(&self) -> bool {
        self.by_column.values().any(|c| c.is_complete())
    }
}

/// Build the resolution for `board`.
///
/// **Once per config load.** The per-issue path is a lookup against the result.
///
/// The legacy reconciliation lives in [`BoardConfiguration::category_for`], which
/// WP01 wrote and this module does not duplicate: a board with no `category_map`
/// resolves its `done_column` to `completed` and everything else to the safe
/// default. Duplicating that fallback here is how a board ends up with two
/// notions of its own default.
pub fn resolution(
    config: &Config,
    board: &BoardConfiguration,
    board_name: &str,
) -> CategoryResolution {
    let mut by_column = HashMap::with_capacity(board.columns.len());
    let mut unmapped = Vec::new();
    for column in &board.columns {
        let key = board.category_for(column, &config.categories);
        // An unmapped-and-not-done column is the one that relied on the default.
        // `category_for` returns the safe default for those, and `category_map`
        // says whether the entry was explicit.
        let explicit = board.category_map.contains_key(column);
        if !explicit {
            unmapped.push(column.clone());
        }
        // `category_for` is total over `columns` because the fallback covers
        // everything, so this cannot be `None`; `from_key` cannot be `None`
        // because config load validated the vocabulary. Both are `expect`ed with
        // the reason rather than defaulted, so a violated invariant is loud.
        let category = WorkflowCategory::from_key(key).unwrap_or_else(|| {
            unreachable!("config load rejected the vocabulary, so `{key}` is in it")
        });
        by_column.insert(column.clone(), category);
    }
    CategoryResolution {
        by_column,
        order: board.columns.clone(),
        default_applied: !unmapped.is_empty(),
        explicit_policy: !board.category_map.is_empty(),
        unmapped,
        board: board_name.to_string(),
    }
}

/// The single completion decision (contract §4).
///
/// True only when the issue's column maps to `completed`. `canceled` is terminal
/// and **not** complete, and an unmapped column resolves to the safe default, so
/// it is never silently counted as done.
///
/// Never errors: an issue in a column the board does not configure is not
/// complete. That is a board that failed validation, not a reason to fail a read.
pub fn is_completed(issue: &Issue, resolution: &CategoryResolution) -> bool {
    resolution
        .resolve(issue.status.display())
        .is_some_and(WorkflowCategory::is_complete)
}

/// The board's **completion column**, chosen by category rather than by
/// `done_column` (WP09).
///
/// ## Why this exists
///
/// `BoardConfiguration::effective_done_column()` answers a *config* question — "what
/// did the author name?" — and on a board with a `category_map` it is not the same
/// question as "which column is complete?". A board whose map puts `completed` on
/// `shipped` while `done_column` is `done` has two different answers, and every
/// consumer that asked the config question got the wrong one.
///
/// That is not hypothetical. The blocked-move guard — the previous mission's central
/// feature — read `done_column` and early-returned for any other column, so on such
/// a board:
///
/// - a **blocked** issue moved into `shipped` (genuinely complete) got **no
///   warning, no `--yes` requirement, and no `blocked_move_acknowledged` History
///   entry**; and
/// - moving it to `done` (not complete at all) **did** demand confirmation, because
///   that is the column the config named.
///
/// The guard was silently disabled on exactly the boards this mission exists to
/// support. Found by the call-site audit T038 step 4 asks for, which is the argument
/// for having one: the pattern is five lines long and the consequence is a safety
/// check that does not run.
///
/// ## Which column, when several are complete
///
/// The **first** configured column whose category is complete, in board order. A
/// board with two completed columns has no single completion column, and the first is
/// the only choice that does not depend on iteration order. `None` only for a board
/// that failed validation — nothing resolves to `completed` — which the callers
/// handle rather than this function panicking on a config the caller could not have
/// built.
pub fn completion_column(board: &BoardConfiguration, config: &Config) -> Option<String> {
    let resolution = resolution(config, board, active_board_name(config));
    board
        .columns
        .iter()
        .find(|c| {
            resolution
                .resolve(c)
                .is_some_and(WorkflowCategory::is_complete)
        })
        .cloned()
}

/// The board's completion column, **total**: the first complete column, else the
/// configured `done_column`, else the literal `"done"` (WP09).
///
/// ## Why the fallback lives here and not at each call site
///
/// Three callers need "the completion column, and I cannot have a `None`" because
/// they hand the name to a service that takes it as a parameter
/// (`RelationshipGraph`, `hierarchy_cells`, `blocked_reasons`, `child_markers`).
/// Writing the fallback at each site meant four copies of
/// `.or_else(done_column).unwrap_or("done")` — and one of them drifted, which is how
/// the TUI's blocked marker ended up computed against `done_column` while the CLI's
/// used the service. One function, one fallback, one place to be right.
///
/// The fallback order is deliberate: the service's answer is the **meaning**, a
/// configured `done_column` is a reasonable second guess for a board that failed
/// validation, and the literal is a last resort so a caller that must produce a name
/// always can. Only the first is authoritative, and only the first is ever reached by
/// a config that loads.
pub fn completion_column_or_default(board: &BoardConfiguration, config: &Config) -> String {
    completion_column(board, config)
        .or_else(|| board.effective_done_column().map(str::to_string))
        .unwrap_or_else(|| "done".to_string())
}

/// The issue's category, or `None` for a column the board does not configure.
pub fn category_of(issue: &Issue, resolution: &CategoryResolution) -> Option<WorkflowCategory> {
    resolution.resolve(issue.status.display())
}

/// The fixed diagnostic vocabulary (contract §6).
///
/// One set, so the CLI, TUI, MCP and lint report a violation under the same name
/// rather than four names for one condition.
#[derive(Debug, Clone, Copy, PartialEq, Eq, PartialOrd, Ord, Hash)]
pub enum DiagnosticKind {
    MissingCompletionCategory,
    UnknownCategory,
    MappingForUnknownColumn,
    UnmappedColumnDefault,
    InvalidTransition,
    UnknownColumn,
    DirectEditPolicyViolation,
}

impl DiagnosticKind {
    pub const ALL: [DiagnosticKind; 7] = [
        DiagnosticKind::MissingCompletionCategory,
        DiagnosticKind::UnknownCategory,
        DiagnosticKind::MappingForUnknownColumn,
        DiagnosticKind::UnmappedColumnDefault,
        DiagnosticKind::InvalidTransition,
        DiagnosticKind::UnknownColumn,
        DiagnosticKind::DirectEditPolicyViolation,
    ];

    pub fn as_str(self) -> &'static str {
        match self {
            DiagnosticKind::MissingCompletionCategory => "missing_completion_category",
            DiagnosticKind::UnknownCategory => "unknown_category",
            DiagnosticKind::MappingForUnknownColumn => "mapping_for_unknown_column",
            DiagnosticKind::UnmappedColumnDefault => "unmapped_column_default",
            DiagnosticKind::InvalidTransition => "invalid_transition",
            DiagnosticKind::UnknownColumn => "unknown_column",
            DiagnosticKind::DirectEditPolicyViolation => "direct_edit_policy_violation",
        }
    }
}

/// One finding. The service never writes, so a diagnostic is the only output a
/// refusal produces.
#[derive(Debug, Clone, PartialEq, Eq)]
pub struct WorkflowDiagnostic {
    pub kind: DiagnosticKind,
    /// The board, column, or issue the finding is about, rendered for a message.
    pub subject: String,
    pub message: String,
}

impl fmt::Display for DiagnosticKind {
    /// The contract's fixed name, so a surface that renders a refusal names the
    /// condition the same way every other surface does (contract §6).
    fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
        f.write_str(self.as_str())
    }
}

impl fmt::Display for WorkflowDiagnostic {
    /// `(<kind>) for <subject>: <message>`.
    ///
    /// WP03. The kind leads, in parentheses, because the *name* is the part a
    /// caller can match on — a user reporting a bug, a test asserting the
    /// condition, and a grep over logs all key off it. `subject` sits in the
    /// middle because it says what was attempted, and `message` says why not.
    fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
        write!(f, "({}) for {}: {}", self.kind, self.subject, self.message)
    }
}

/// Configuration findings across every board.
///
/// **Never errors.** It returns a value so lint, the CLI and MCP can consume it
/// directly, and so a caller can decide for itself which findings are fatal.
/// WP01 already refuses the fatal ones at load; what is added here is the
/// board-level reporting WP01 cannot express — chiefly `unmapped_column_default`.
///
/// Deterministic: sorted by board, then column, then kind, so two runs over the
/// same config produce the same list and a test can compare it directly.
pub fn validate_config(config: &Config) -> Vec<WorkflowDiagnostic> {
    let mut out = Vec::new();
    for (name, board) in &config.kanban.configurations {
        let res = resolution(config, board, name);
        if !res.has_completion() {
            out.push(WorkflowDiagnostic {
                kind: DiagnosticKind::MissingCompletionCategory,
                subject: name.clone(),
                message: format!(
                    "no column on board `{name}` resolves to `{COMPLETE_CATEGORY}`, so \\
                     nothing on it is ever complete"
                ),
            });
        }
        for (column, key) in &board.category_map {
            if !board.columns.iter().any(|c| c == column) {
                out.push(WorkflowDiagnostic {
                    kind: DiagnosticKind::MappingForUnknownColumn,
                    subject: format!("{name}.{column}"),
                    message: format!("`{column}` is not a column on board `{name}`"),
                });
            }
            if WorkflowCategory::from_key(key).is_none() {
                out.push(WorkflowDiagnostic {
                    kind: DiagnosticKind::UnknownCategory,
                    subject: format!("{name}.{column}"),
                    message: format!("`{key}` is not in the global category vocabulary"),
                });
            }
        }
        for column in &res.unmapped {
            // WP04: a column whose *default* is the completion category is not a
            // finding. That is the legacy reconciliation this mission settled on
            // (WP01): a board with no `category_map` resolves its `done_column` to
            // `completed` so completion detection works on every existing
            // repository.
            //
            // Reporting it as `unmapped_column_default` — as WP02 did — produced one
            // finding per column on every board in the world, including the column
            // the board *intends* to be done, and each message said it "resolves to
            // the safe default `unstarted`" about a column that had resolved to
            // `completed`. The diagnostic pointed the user at the exact thing that
            // was working.
            //
            // It still belongs in `CategoryResolution::unmapped` — the **policy**
            // opt-in reads that, not this diagnostic. What changed is only whether
            // it is worth telling someone about.
            let resolved = res.resolve(column);
            if resolved.is_some_and(WorkflowCategory::is_complete) {
                continue;
            }
            out.push(WorkflowDiagnostic {
                kind: DiagnosticKind::UnmappedColumnDefault,
                subject: format!("{name}.{column}"),
                message: format!(
                    "column `{column}` has no `category_map` entry, so it resolves to the \\
                     safe default `{}`",
                    resolved
                        .map(|c| c.key())
                        .unwrap_or(config.categories.default.as_str())
                ),
            });
        }
    }
    out.sort_by(|a, b| {
        a.subject
            .cmp(&b.subject)
            .then_with(|| a.kind.cmp(&b.kind))
            .then_with(|| a.message.cmp(&b.message))
    });
    out
}

/// An explicit override out of a terminal category.
#[derive(Debug, Clone, PartialEq, Eq)]
pub struct TransitionOverride {
    /// Why. Required: an override with no reason is not recorded as one, because
    /// a bare "I did it anyway" is indistinguishable from a mistake.
    pub reason: String,
}

/// The outcome of judging a transition.
#[derive(Debug, Clone, PartialEq, Eq)]
pub enum TransitionOutcome {
    /// Legal. `changed` is false for a same-column transition, which is permitted
    /// and idempotent — no decision to append, no write.
    Accepted {
        from: String,
        to: String,
        from_category: WorkflowCategory,
        to_category: WorkflowCategory,
        changed: bool,
        /// The override, when one was supplied and used.
        override_reason: Option<String>,
    },
    /// Refused. Nothing is written, including no History entry (contract §3.5).
    Rejected(WorkflowDiagnostic),
}

/// The name of the board [`Config::default_config`] resolves to.
///
/// WP04. `default_config` is a lookup of `"default"` falling back to the first
/// declared board, and re-deriving that at a call site would be a second copy of
/// a rule that decides *which* board the whole program operates on. A diagnostic
/// naming a different board than the one consulted would be worse than no name.
///
/// Returns `"default"` when the config has no board at all, which
/// `Config::validate` already rejects; the fallback exists so a diagnostic is
/// never the thing that panics.
pub fn active_board_name(config: &Config) -> &str {
    config
        .kanban
        .configurations
        .keys()
        .find(|name| name.as_str() == "default")
        .map(String::as_str)
        .or_else(|| {
            config
                .kanban
                .configurations
                .keys()
                .next()
                .map(String::as_str)
        })
        .unwrap_or("default")
}

/// The [`CategoryResolution`] for the active board, plus that board's name.
///
/// WP04. Every surface needs the same pair — the seam to judge a transition, and
/// `tix status` / `tix list` / `tix workflow show` to render a category — and
/// building the resolution ad hoc at each site is how one of them ends up
/// consulting a different board than the others. The name comes back alongside
/// because every one of those renderers has to name the board it consulted.
pub fn active_resolution(config: &Config) -> (String, CategoryResolution) {
    let name = active_board_name(config);
    let resolution = resolution(config, config.default_config(), name);
    (name.to_string(), resolution)
}

/// One direct-edit finding: a file whose `status` no longer agrees with its History.
///
/// WP06. Separate from [`WorkflowDiagnostic`] because it has to carry **both** sides
/// of the contradiction — the recorded `from` and the current column — and a message
/// that names the rule. A `WorkflowDiagnostic` reports a condition; this reports a
/// disagreement between a record and a file, which is a different thing to say.
#[derive(Debug, Clone, PartialEq, Eq)]
pub struct DirectEditFinding {
    /// The issue number, so a caller can find the file without re-parsing.
    pub number: u32,
    pub kind: DiagnosticKind,
    /// The column the accepted decision landed in, or `None` when the file records
    /// no usable decision at all.
    pub recorded: Option<String>,
    /// The column the file says now.
    pub current: String,
    /// The rule that was broken, in words.
    pub message: String,
}

/// Report files whose `status` contradicts their own History (contract §5, C-005).
///
/// ## What it does and does not conclude
///
/// Two conditions, and both are conclusions about the *record*, not about intent:
///
/// 1. **The status diverged from the last accepted decision.** The file's History
///    says a transition landed in `recorded`; the file says `current`. Something
///    changed the column without going through the seam.
/// 2. **The recorded decision contradicts the current policy.** The decision was
///    accepted; re-evaluating it now is refused — the terminal lock, or adjacency.
///    A board's `category_map` may have been tightened since, and the historical
///    decision is still a true record of what happened then.
///
/// ## What is deliberately *not* a violation
///
/// **A file with no decision at all.** An issue created directly into a column has
/// no transition to record, and creating one in a terminal column is legal — there
/// is no `from` to judge. Reporting every such file would fire on every issue in a
/// repository that has never been moved, which is lint's characteristic failure mode:
/// a finding nobody reads.
///
/// A **same-column** decision record is likewise not a violation. The seam never
/// writes one, but a hand-edited file can contain one, and it records no move.
///
/// ## Never writes
///
/// This function, and everything that calls it, is **observational**. It does not
/// repair the file, does not append a History entry, does not rewrite existing
/// History, and offers no "fix" affordance (C-005, decision
/// `01M3C3XBMTR5WFV7059NXM04AJ`). A hand-edited file stays exactly as the user left
/// it and stays readable; the contradiction is theirs to resolve.
///
/// ## One pass, deterministic order
///
/// A single sweep, not one per rule, and each file reported **once** — a file that
/// diverged *and* whose decision now contradicts policy is one finding naming the
/// stronger of the two, not two findings for one root cause.
pub fn lint_direct_edits(
    issues: &[Issue],
    resolution: &CategoryResolution,
    config: &Config,
) -> Vec<DirectEditFinding> {
    let mut out: Vec<DirectEditFinding> = Vec::new();
    for issue in issues {
        let current = issue.status.display().to_string();
        // The last *usable* decision. `History::events()` skips lines it could not
        // parse, so a corrupted `transition_accepted` line reads here as "no
        // decision" — which is why the no-decision case is not a violation. The
        // alternative would be a diagnostic for a corrupt audit line, and the
        // contract's seven names do not include one; inventing an eighth is
        // exactly the kind of claim the shared vocabulary exists to prevent.
        let decision = issue
            .history
            .events()
            .iter()
            .rev()
            .filter(|e| e.kind == crate::model::HistoryEventKind::TransitionAccepted)
            .find_map(|e| crate::model::TransitionDecision::from_event(e).ok())
            .filter(|d| !d.is_no_op());

        let Some(decision) = decision else {
            continue;
        };

        if decision.to != current {
            out.push(DirectEditFinding {
                number: issue.number,
                kind: DiagnosticKind::DirectEditPolicyViolation,
                recorded: Some(decision.to.clone()),
                current: current.clone(),
                message: format!(
                    "status is `{current}` but this issue's History records the last \
                     accepted transition as landing in `{}`; the file was changed \
                     outside `tix`",
                    decision.to
                ),
            });
            continue;
        }

        // The status agrees with the record, so the only remaining question is
        // whether the recorded move still satisfies policy. Re-evaluated against the
        // *current* config, which is the point: a tightened `category_map` makes a
        // historical decision look wrong, and that is worth knowing even though the
        // record is accurate.
        //
        // `is_compatible(from, to, …)`, **not** `validate_transition(issue, from, …)`.
        // The first version used the latter and evaluated the *current* column back
        // to the recorded `from` — so it judged the reverse of the decision that was
        // actually recorded, and reported every legal forward move in the repository
        // as a policy violation. `is_compatible` is the predicate for exactly this
        // question: "may this pair of columns move?" without inventing an issue.
        let from = decision.from.clone();
        let to = decision.to.clone();
        if !is_compatible(&from, &to, resolution, config) {
            out.push(DirectEditFinding {
                number: issue.number,
                kind: DiagnosticKind::DirectEditPolicyViolation,
                recorded: Some(to.clone()),
                current,
                message: format!(
                    "the accepted transition recorded in this issue's History \
                     (`{from}` -> `{to}`) is no longer permitted by the current \
                     policy; the record is accurate but the board's category mapping \
                     has since changed"
                ),
            });
        }
    }
    // Deterministic: by issue number, then by the columns involved. Two runs over the
    // same tree must produce the same list, byte for byte (contract §5).
    out.sort_by(|a, b| {
        a.number
            .cmp(&b.number)
            .then_with(|| a.current.cmp(&b.current))
            .then_with(|| a.recorded.cmp(&b.recorded))
    });
    out
}

/// The pure compatibility predicate behind [`validate_transition`].
///
/// Separated so the policy is testable without constructing a decision, and so a
/// caller that only wants to know "may this move?" does not have to invent a
/// decision to ask. Never errors: an unconfigured column is simply incompatible.
pub fn is_compatible(
    from_column: &str,
    to_column: &str,
    resolution: &CategoryResolution,
    config: &Config,
) -> bool {
    // Category policy — the terminal lock and adjacency alike — is **opt in**,
    // gated on `explicit_policy`. WP03: a board that never declared a
    // `category_map` gets the completion definition and the commit-clearing rule
    // and nothing else, because those are about *what* a column means while
    // policy is about *what may change*.
    //
    // The two are gated together deliberately, and they have to be. On a legacy
    // board every non-done column resolves to the single `unstarted` category, so
    // adjacency's "may not move backwards in the declared order" is exactly the
    // terminal lock minus the reasoned override — `completed` is last in the
    // vocabulary, so every exit from it is also backwards. Gating only the lock
    // would therefore have left adjacency to refuse the very moves the lock was
    // relaxed to allow, with a message that does not mention an override. The
    // first version of this change did exactly that, and its two TUI tests stayed
    // red.
    let policy_applies = config.transitions.terminal_locked && resolution.explicit_policy;

    // Same column is permitted and idempotent, whatever the category (contract §3.2).
    if from_column == to_column {
        return true;
    }
    let (Some(from), Some(to)) = (
        resolution.resolve(from_column),
        resolution.resolve(to_column),
    ) else {
        return false;
    };
    // The terminal lock is category-level, so it is written once here rather than
    // per column pair.
    if policy_applies && from.is_terminal() && !to.is_terminal() {
        return false;
    }
    // Adjacency: a category may move to itself or forward through the declared
    // order. Going backwards is what a policy rule restricts, and expressing it on
    // the order means a board with custom column names needs no configuration for
    // it to behave.
    if !policy_applies {
        return true;
    }
    let order = |c: WorkflowCategory| {
        config
            .categories
            .order
            .iter()
            .position(|k| k == c.key())
            .unwrap_or(usize::MAX)
    };
    order(to) >= order(from)
}

/// The single transition evaluation (contract §3).
///
/// The only place legality is decided. A surface that judges a transition on its
/// own is a parity defect.
pub fn validate_transition(
    issue: &Issue,
    target_column: &str,
    resolution: &CategoryResolution,
    config: &Config,
    override_reason: Option<&str>,
) -> TransitionOutcome {
    let from_column = issue.status.display().to_string();
    let reject = |kind: DiagnosticKind, message: String| {
        TransitionOutcome::Rejected(WorkflowDiagnostic {
            kind,
            subject: format!("{from_column} -> {target_column}"),
            message,
        })
    };

    // 1. Unknown column.
    //
    // WP03: the valid-column list moved in from `mv.rs`, which used to carry its
    // own copy of this check so it could print the list. Two copies of the rule
    // is what C-003 forbids, and the copy in `mv.rs` is gone — but its message was
    // the more useful of the two, because a user who mistypes a column needs to be
    // told what to type instead. So the list is *widened into* the service rather
    // than dropped with it: one rule, and the better message.
    let Some(to_category) = resolution.resolve(target_column) else {
        return reject(
            DiagnosticKind::UnknownColumn,
            format!(
                "`{target_column}` is not a column on board `{}`; valid columns: {}",
                resolution.board,
                resolution.column_list()
            ),
        );
    };
    let Some(from_category) = resolution.resolve(&from_column) else {
        return reject(
            DiagnosticKind::UnknownColumn,
            format!(
                "issue is in `{from_column}`, which is not a column on board `{}`; \
                 valid columns: {}",
                resolution.board,
                resolution.column_list()
            ),
        );
    };

    // 2. Same column: permitted, idempotent, and no decision to append.
    if from_column == target_column {
        return TransitionOutcome::Accepted {
            from: from_column,
            to: target_column.to_string(),
            from_category,
            to_category,
            changed: false,
            override_reason: None,
        };
    }

    // 3. Terminal lock, with the reasoned escape hatch.
    //
    // Gated on `explicit_policy`, together with adjacency in `is_compatible` —
    // see that function's note for why the two cannot be gated separately.
    let reason = override_reason.map(str::trim).filter(|r| !r.is_empty());
    if config.transitions.terminal_locked
        && resolution.explicit_policy
        && from_category.is_terminal()
        && !to_category.is_complete()
        && !to_category.is_terminal()
    {
        return match reason {
            Some(reason) => TransitionOutcome::Accepted {
                from: from_column,
                to: target_column.to_string(),
                from_category,
                to_category,
                changed: true,
                override_reason: Some(reason.to_string()),
            },
            None => reject(
                DiagnosticKind::InvalidTransition,
                // WP04: the message names the **spelling** of the override.
                //
                // It previously ended at "needs an explicit override with a reason",
                // which tells a user the rule and leaves them to guess the flag. The
                // rendered string also carried a Rust line-continuation `\` into the
                // output, because the `\\` in the source literal survives into the
                // format string — so the message a user saw contained a stray
                // backslash in the middle of a sentence. Both are fixed by writing
                // the sentence as one line with an explicit em dash.
                format!(
                    "issue is in terminal category `{}`; moving to `{target_column}` \
                     (`{}`) needs an explicit override with a reason \u{2014} \
                     `tix mv <issue> {target_column} --reason \"why\"`",
                    from_category.key(),
                    to_category.key()
                ),
            ),
        };
    }

    // 4. Adjacency.
    if !is_compatible(&from_column, target_column, resolution, config) {
        return reject(
            DiagnosticKind::InvalidTransition,
            format!(
                "`{}` -> `{}` is not permitted by the category policy",
                from_category.key(),
                to_category.key()
            ),
        );
    }

    TransitionOutcome::Accepted {
        from: from_column,
        to: target_column.to_string(),
        from_category,
        to_category,
        changed: true,
        override_reason: reason.map(str::to_string),
    }
}

/// The documented safe default, re-exported so a surface reporting a defaulted
/// column quotes the same constant the resolution used.
pub const SAFE_DEFAULT: &str = SAFE_DEFAULT_CATEGORY;

#[cfg(test)]
mod tests {
    use super::*;
    use crate::config::BoardConfiguration;
    use indexmap::IndexMap;

    fn board(columns: &[&str], done: &str, map: &[(&str, &str)]) -> BoardConfiguration {
        let mut category_map = IndexMap::new();
        for (column, category) in map {
            category_map.insert((*column).to_string(), (*category).to_string());
        }
        BoardConfiguration {
            columns: columns.iter().map(|c| (*c).to_string()).collect(),
            done_column: Some(done.to_string()),
            category_map,
            hidden_columns: vec![],
            show_mismatch: false,
            wrap_titles: true,
            title_lines: 3,
            card_order: vec![],
            order_by: crate::config::OrderBy::CreatedAtDesc,
        }
    }

    fn config_with(board: BoardConfiguration) -> Config {
        let mut config = Config::default();
        config
            .kanban
            .configurations
            .insert("default".to_string(), board);
        config
    }

    /// A board with its own column names, fully mapped.
    fn custom_config() -> Config {
        config_with(board(
            &["triage", "wip", "review", "shipped"],
            "shipped",
            &[
                ("triage", "backlog"),
                ("wip", "active"),
                ("review", "active"),
                ("shipped", "completed"),
            ],
        ))
    }

    /// An issue in `column`. `Issue` has no `Default`, so it is written out: a
    /// derived default would hide a field added to the model behind a silently
    /// zero value, which is the same failure as a test that measures nothing.
    fn issue_in(column: &str) -> Issue {
        Issue {
            number: 1,
            title: "T".into(),
            status: crate::model::Status::new(column),
            labels: vec![],
            priority: crate::model::Priority::Medium,
            assignee: None,
            estimate: None,
            commit: None,
            gitlab_id: None,
            linear_id: None,
            mission: None,
            task: None,
            relationships: vec![],
            files: vec![],
            cycles: None,
            milestones: None,
            reviewer: None,
            start_date: None,
            due_date: None,
            created: "2026-01-01".into(),
            updated: "2026-01-01".into(),
            filename: "t.md".into(),
            body: String::new(),
            history: crate::model::History::new(),
            has_retired_links_key: false,
            parent: None,
            extra_frontmatter: std::collections::BTreeMap::new(),
            archived: false,
            entered_at: None,
            source: None,
        }
    }

    // -- T006: the vocabulary ------------------------------------------------

    #[test]
    fn every_key_round_trips() {
        for (i, category) in WorkflowCategory::ALL.iter().enumerate() {
            assert_eq!(
                WorkflowCategory::from_key(category.key()),
                Some(*category),
                "{:?} must parse back to itself",
                category
            );
            // And the order agrees with the vocabulary constant WP01 exported, so
            // the two cannot drift.
            assert_eq!(category.key(), CATEGORY_KEYS[i]);
        }
        assert_eq!(WorkflowCategory::ALL.len(), CATEGORY_KEYS.len());
    }

    #[test]
    fn an_unknown_key_yields_none_and_never_a_default() {
        // The `Option` is the point: a typo must be an error, not a silent
        // fallback to `unstarted`.
        for key in ["wontfix", "Done", "COMPLETED", "", " done", "unstarted "] {
            assert_eq!(
                WorkflowCategory::from_key(key),
                None,
                "`{key}` must not resolve to a category"
            );
        }
    }

    #[test]
    fn only_completed_and_canceled_are_terminal() {
        let terminal: Vec<&str> = WorkflowCategory::ALL
            .iter()
            .filter(|c| c.is_terminal())
            .map(|c| c.key())
            .collect();
        assert_eq!(terminal, vec!["completed", "canceled"]);
        // Terminal is not the same claim as complete.
        assert!(WorkflowCategory::Canceled.is_terminal());
        assert!(!WorkflowCategory::Canceled.is_complete());
        assert!(WorkflowCategory::Completed.is_complete());
        assert_eq!(COMPLETE_CATEGORY, "completed");
    }

    #[test]
    fn labels_are_distinct() {
        let mut labels: Vec<&str> = WorkflowCategory::ALL.iter().map(|c| c.label()).collect();
        labels.sort_unstable();
        let before = labels.len();
        labels.dedup();
        assert_eq!(labels.len(), before, "two categories share a display label");
    }

    /// A colour is presentation. Asserted as inert rather than merely present: the
    /// point of the contract clause is that no decision reads it.
    #[test]
    fn color_hint_is_inert_with_respect_to_completion() {
        for category in WorkflowCategory::ALL {
            let hint = category.color_hint();
            if category.is_complete() {
                assert_eq!(hint, Some(ColorHint::Ok));
            }
            // Whatever the hint, the completion answer is the category's alone.
            assert_eq!(
                category.is_complete(),
                category.key() == COMPLETE_CATEGORY,
                "{category:?}: the hint must not decide completion"
            );
        }
    }

    // -- T007: resolution ----------------------------------------------------

    #[test]
    fn an_explicit_mapping_resolves_and_nothing_is_unmapped() {
        let config = custom_config();
        let res = resolution(&config, config.default_config(), "default");
        assert_eq!(res.resolve("triage"), Some(WorkflowCategory::Backlog));
        assert_eq!(res.resolve("wip"), Some(WorkflowCategory::Active));
        assert_eq!(res.resolve("shipped"), Some(WorkflowCategory::Completed));
        assert!(res.unmapped.is_empty());
        assert!(!res.default_applied);
        assert!(res.has_completion());
    }

    #[test]
    fn an_unmapped_column_resolves_to_the_safe_default_and_is_recorded() {
        let config = config_with(board(
            &["triage", "wip", "review", "shipped"],
            "shipped",
            &[
                ("triage", "backlog"),
                ("review", "active"),
                ("shipped", "completed"),
            ],
        ));
        let res = resolution(&config, config.default_config(), "default");
        assert_eq!(res.resolve("wip"), Some(WorkflowCategory::Unstarted));
        assert_eq!(
            res.unmapped,
            vec!["wip".to_string()],
            "recorded, in board order"
        );
        assert!(res.default_applied);
    }

    #[test]
    fn a_custom_named_completion_column_resolves_to_completed() {
        let config = custom_config();
        let res = resolution(&config, config.default_config(), "default");
        // The column is called `shipped`, not `done`. Completion is the category,
        // not the name — which is the whole point of the mapping.
        assert_ne!(
            config.default_config().effective_done_column(),
            Some("done")
        );
        assert_eq!(res.resolve("shipped"), Some(WorkflowCategory::Completed));
        assert!(res.has_completion());
    }

    #[test]
    fn an_unconfigured_column_yields_none() {
        let config = custom_config();
        let res = resolution(&config, config.default_config(), "default");
        assert_eq!(res.resolve("nope"), None);
    }

    /// A legacy board with no `category_map`: `done_column` completes, everything
    /// else is the safe default. WP01 owns the fallback; this asserts the service
    /// reads it rather than duplicating it.
    #[test]
    fn a_legacy_board_with_no_map_completes_on_its_done_column() {
        let config = config_with(board(
            &["todo", "in progress", "in review", "done"],
            "done",
            &[],
        ));
        let res = resolution(&config, config.default_config(), "default");
        assert_eq!(res.resolve("done"), Some(WorkflowCategory::Completed));
        assert_eq!(res.resolve("todo"), Some(WorkflowCategory::Unstarted));
        assert!(res.has_completion());
    }

    #[test]
    fn two_resolutions_of_the_same_config_are_equal() {
        let config = custom_config();
        let a = resolution(&config, config.default_config(), "default");
        let b = resolution(&config, config.default_config(), "default");
        assert_eq!(
            a, b,
            "resolution must be a function of the config, not of when it ran"
        );
    }

    // -- T008: the single completion decision ---------------------------------

    #[test]
    fn completion_is_the_category_alone() {
        let config = config_with(board(
            &["triage", "wip", "dropped", "shipped"],
            "shipped",
            &[
                ("triage", "backlog"),
                ("wip", "active"),
                ("dropped", "canceled"),
                ("shipped", "completed"),
            ],
        ));
        let res = resolution(&config, config.default_config(), "default");
        assert!(is_completed(&issue_in("shipped"), &res));
        // `canceled` is terminal and **not** complete — the distinction triage's
        // decline action depends on.
        assert!(!is_completed(&issue_in("dropped"), &res));
        assert!(!is_completed(&issue_in("wip"), &res));
        // An unconfigured column is not complete, and does not error.
        assert!(!is_completed(&issue_in("nope"), &res));
        assert_eq!(
            category_of(&issue_in("dropped"), &res),
            Some(WorkflowCategory::Canceled)
        );
        assert_eq!(category_of(&issue_in("nope"), &res), None);
    }

    // -- T009: transition policy ---------------------------------------------

    #[test]
    fn a_compatible_transition_is_accepted() {
        let config = custom_config();
        let res = resolution(&config, config.default_config(), "default");
        let outcome = validate_transition(&issue_in("triage"), "wip", &res, &config, None);
        match outcome {
            TransitionOutcome::Accepted {
                from,
                to,
                changed,
                override_reason,
                from_category,
                to_category,
            } => {
                assert_eq!((from.as_str(), to.as_str()), ("triage", "wip"));
                assert_eq!(from_category, WorkflowCategory::Backlog);
                assert_eq!(to_category, WorkflowCategory::Active);
                assert!(changed);
                assert_eq!(override_reason, None);
            }
            other @ TransitionOutcome::Rejected(_) => {
                panic!("expected acceptance, got {other:?}")
            }
        }
    }

    /// Contract §3.2 and the intake's third invariant: a same-column transition is
    /// permitted, idempotent, and produces no decision to append.
    #[test]
    fn a_same_column_transition_is_idempotent_with_no_decision() {
        let config = custom_config();
        let res = resolution(&config, config.default_config(), "default");
        for column in ["triage", "wip", "review", "shipped"] {
            match validate_transition(&issue_in(column), column, &res, &config, None) {
                TransitionOutcome::Accepted { changed, .. } => {
                    assert!(!changed, "`{column}` -> `{column}` must be a no-op")
                }
                TransitionOutcome::Rejected(other) => {
                    panic!("expected acceptance for `{column}`, got {other:?}")
                }
            }
        }
    }

    #[test]
    fn an_unknown_target_column_is_rejected() {
        let config = custom_config();
        let res = resolution(&config, config.default_config(), "default");
        match validate_transition(&issue_in("wip"), "nowhere", &res, &config, None) {
            TransitionOutcome::Rejected(d) => {
                assert_eq!(d.kind, DiagnosticKind::UnknownColumn)
            }
            TransitionOutcome::Accepted { .. } => {
                panic!("expected a rejection, got an accepted transition")
            }
        }
    }

    /// The terminal lock, and the reasoned escape hatch. The override must carry a
    /// reason: a bare "I did it anyway" is indistinguishable from a mistake.
    #[test]
    fn a_terminal_exit_is_refused_without_a_reason_and_allowed_with_one() {
        let config = config_with(board(
            &["triage", "wip", "dropped", "shipped"],
            "shipped",
            &[
                ("triage", "backlog"),
                ("wip", "active"),
                ("dropped", "canceled"),
                ("shipped", "completed"),
            ],
        ));
        let res = resolution(&config, config.default_config(), "default");

        // Out of a terminal category into a non-terminal one: refused.
        for from in ["dropped", "shipped"] {
            match validate_transition(&issue_in(from), "wip", &res, &config, None) {
                TransitionOutcome::Rejected(d) => {
                    assert_eq!(d.kind, DiagnosticKind::InvalidTransition, "from `{from}`")
                }
                TransitionOutcome::Accepted { .. } => {
                    panic!("expected a rejection from `{from}`")
                }
            }
            // A blank reason is not a reason.
            match validate_transition(&issue_in(from), "wip", &res, &config, Some("   ")) {
                TransitionOutcome::Rejected(_) => {}
                TransitionOutcome::Accepted { .. } => {
                    panic!("a blank override must not unlock `{from}`")
                }
            }
            // A real one is accepted and recorded.
            match validate_transition(&issue_in(from), "wip", &res, &config, Some("wrong call")) {
                TransitionOutcome::Accepted {
                    override_reason,
                    changed,
                    ..
                } => {
                    assert_eq!(override_reason.as_deref(), Some("wrong call"));
                    assert!(changed);
                }
                TransitionOutcome::Rejected(d) => {
                    panic!("a reasoned override must be accepted, got: {}", d.message)
                }
            }
        }
    }

    /// Terminal to terminal is not an **exit**, so the lock does not apply.
    ///
    /// The first version of this test moved `canceled -> completed` and failed. The
    /// lock was not what refused it: `canceled` is *after* `completed` in the
    /// declared order, so **adjacency** refused it. The two rules are independent
    /// and the test conflated them. `completed -> canceled` is terminal to
    /// terminal *and* forward, so the lock is the only rule that could have applied
    /// and it does not.
    #[test]
    fn a_terminal_to_terminal_move_is_not_locked() {
        let config = config_with(board(
            &["triage", "dropped", "shipped"],
            "shipped",
            &[
                ("triage", "backlog"),
                ("dropped", "canceled"),
                ("shipped", "completed"),
            ],
        ));
        let res = resolution(&config, config.default_config(), "default");
        assert!(matches!(
            validate_transition(&issue_in("shipped"), "dropped", &res, &config, None),
            TransitionOutcome::Accepted { .. }
        ));
        // And the backwards direction is still refused — by adjacency, which is a
        // different rule and a different answer for a different reason.
        match validate_transition(&issue_in("dropped"), "shipped", &res, &config, None) {
            TransitionOutcome::Rejected(d) => {
                assert_eq!(d.kind, DiagnosticKind::InvalidTransition);
                assert!(
                    d.message.contains("category policy"),
                    "refused by adjacency, not the lock: {}",
                    d.message
                );
            }
            TransitionOutcome::Accepted { .. } => {
                panic!("expected a rejection, got an accepted transition")
            }
        }
    }

    /// The lock is a **separate** rule, and this is the only configuration where
    /// it is the *sole* thing preventing a move.
    ///
    /// With the declared order (`... completed, canceled` last), every exit from a
    /// terminal category is also *backwards*, so adjacency refuses it regardless and
    /// the lock is redundant. Putting `canceled` first in the order makes the exit
    /// forward, which isolates the lock: with it on the move is refused, with it off
    /// the move is permitted. Without this ordering the switch-off would prove
    /// nothing — the move would be refused either way, and the test would pass
    /// while measuring adjacency.
    #[test]
    fn the_terminal_lock_can_be_switched_off() {
        let mut config = config_with(board(
            &["triage", "dropped", "shipped"],
            "shipped",
            &[
                ("triage", "backlog"),
                ("dropped", "canceled"),
                ("shipped", "completed"),
            ],
        ));
        config.categories.order = vec![
            "canceled".into(),
            "backlog".into(),
            "active".into(),
            "completed".into(),
        ];
        let res = resolution(&config, config.default_config(), "default");

        // Precondition, stated on the *order* rather than on `is_compatible`:
        // `is_compatible` applies the lock too, so asking it "is adjacency
        // permitting this?" cannot be done through it. With `canceled` before
        // `backlog`, adjacency permits the move and the lock is the only thing
        // standing in its way.
        let pos = |key: &str| {
            config
                .categories
                .order
                .iter()
                .position(|k| k == key)
                .expect("both keys are in the order")
        };
        assert!(
            pos("canceled") < pos("backlog"),
            "precondition: the move is forward"
        );
        assert!(matches!(
            validate_transition(&issue_in("dropped"), "triage", &res, &config, None),
            TransitionOutcome::Rejected { .. }
        ));

        config.transitions.terminal_locked = false;
        let res = resolution(&config, config.default_config(), "default");
        assert!(matches!(
            validate_transition(&issue_in("dropped"), "triage", &res, &config, None),
            TransitionOutcome::Accepted { changed: true, .. }
        ));
    }

    /// Adjacency is expressed on the *category* order, so a board with custom
    /// column names needs no per-pair configuration for it to behave.
    #[test]
    fn a_backwards_category_move_is_rejected() {
        let config = custom_config();
        let res = resolution(&config, config.default_config(), "default");
        // `active` is later than `backlog` in the vocabulary, so going back is not
        // permitted; a same-category move between two active columns is.
        assert!(!is_compatible("review", "triage", &res, &config));
        assert!(is_compatible("triage", "review", &res, &config));
        assert!(is_compatible("wip", "review", &res, &config));
        match validate_transition(&issue_in("review"), "triage", &res, &config, None) {
            TransitionOutcome::Rejected(d) => assert_eq!(d.kind, DiagnosticKind::InvalidTransition),
            TransitionOutcome::Accepted { .. } => {
                panic!("expected a rejection, got an accepted transition")
            }
        }
    }

    /// Rejection is inert: the service returns a diagnostic and writes nothing.
    /// Asserted as a property of the return type's shape — there is no file, no
    /// store and no `Result` in the signature to write through.
    #[test]
    fn a_rejection_carries_a_diagnostic_and_nothing_else() {
        let config = custom_config();
        let res = resolution(&config, config.default_config(), "default");
        let outcome = validate_transition(&issue_in("review"), "triage", &res, &config, None);
        let TransitionOutcome::Rejected(d) = outcome else {
            panic!("expected a rejection")
        };
        assert!(!d.message.is_empty());
        assert!(!d.subject.is_empty());
    }

    // -- T010: configuration diagnostics -------------------------------------

    #[test]
    fn a_clean_config_reports_nothing() {
        let config = custom_config();
        assert_eq!(validate_config(&config), vec![]);
    }

    #[test]
    fn a_board_with_no_completion_column_is_reported() {
        // Built directly, since config load refuses it — the service reports the
        // same condition under the same name rather than being the second rule.
        let config = config_with(board(
            &["triage", "wip", "shipped"],
            "shipped",
            &[("triage", "backlog"), ("wip", "active")],
        ));
        let found: Vec<DiagnosticKind> = validate_config(&config)
            .into_iter()
            .map(|d| d.kind)
            .collect();
        assert!(
            found.contains(&DiagnosticKind::MissingCompletionCategory),
            "got {found:?}"
        );
    }

    #[test]
    fn an_unmapped_column_is_reported_but_is_not_an_error() {
        let config = config_with(board(
            &["triage", "wip", "shipped"],
            "shipped",
            &[("shipped", "completed")],
        ));
        let found: Vec<DiagnosticKind> = validate_config(&config)
            .into_iter()
            .map(|d| d.kind)
            .collect();
        assert!(
            found.contains(&DiagnosticKind::UnmappedColumnDefault),
            "got {found:?}"
        );
        // Reported, never fatal: `validate_config` returns a value and does not
        // error, and a defaulted column resolves (WP01 proved that at load).
        assert!(!found.contains(&DiagnosticKind::UnknownColumn));
    }

    #[test]
    fn an_unknown_column_and_category_are_reported() {
        let config = config_with(board(
            &["triage", "shipped"],
            "shipped",
            &[
                ("triage", "backlog"),
                ("shipped", "completed"),
                ("nowhere", "active"),
            ],
        ));
        let found: Vec<DiagnosticKind> = validate_config(&config)
            .into_iter()
            .map(|d| d.kind)
            .collect();
        assert!(
            found.contains(&DiagnosticKind::MappingForUnknownColumn),
            "{found:?}"
        );
    }

    #[test]
    fn two_runs_return_equal_results() {
        let config = config_with(board(
            &["triage", "wip", "shipped"],
            "shipped",
            &[("shipped", "completed"), ("nowhere", "wontfix")],
        ));
        assert_eq!(validate_config(&config), validate_config(&config));
        // And deterministically ordered, not merely equal run to run.
        let subjects: Vec<String> = validate_config(&config)
            .into_iter()
            .map(|d| d.subject)
            .collect();
        let mut sorted = subjects.clone();
        sorted.sort();
        assert_eq!(subjects, sorted, "diagnostics must be sorted by subject");
    }

    #[test]
    fn the_diagnostic_kind_set_is_the_contract_set() {
        let names: Vec<&str> = DiagnosticKind::ALL.iter().map(|k| k.as_str()).collect();
        assert_eq!(
            names,
            vec![
                "missing_completion_category",
                "unknown_category",
                "mapping_for_unknown_column",
                "unmapped_column_default",
                "invalid_transition",
                "unknown_column",
                "direct_edit_policy_violation",
            ],
            "contract §6 fixes these names; every surface shares them"
        );
        // And they round-trip through nothing: `as_str` is the only spelling.
        for kind in DiagnosticKind::ALL {
            assert!(!kind.as_str().is_empty());
        }
    }

    /// NFR-001's gate: the per-issue path is a hash lookup, not a scan. Measured
    /// against a deliberately wasteful re-resolution, which is the failure mode.
    #[test]
    fn the_per_issue_path_is_a_lookup_not_a_rebuild() {
        let config = custom_config();
        let board = config.default_config();
        let res = resolution(&config, board, "default");
        let build = std::time::Instant::now();
        for _ in 0..2_000 {
            let _ = resolution(&config, board, "default");
        }
        let rebuild_cost = build.elapsed();
        let lookup = std::time::Instant::now();
        for _ in 0..2_000 {
            let _ = res.resolve("wip");
        }
        let lookup_cost = lookup.elapsed();
        assert!(
            lookup_cost < rebuild_cost,
            "2,000 lookups ({lookup_cost:?}) must cost less than 2,000 rebuilds \
             ({rebuild_cost:?}) — resolution is built once and read many times"
        );
    }
}