car-verify 0.52.0

//! Temporal policies over an execution **trace**, not a plan.
//!
//! CAR could express "never call this tool" but not "never call this tool
//! before that one succeeded in this run". The two existing mechanisms each
//! stop short:
//!
//! * `car-policy` rules (`deny_tool`, `deny_keyword`, `deny_tool_param`) are
//!   stateless single-action predicates — each is evaluated against one action
//!   in isolation, and nothing consults what has already happened.
//! * [`crate::workflow_graph::TemporalPolicy`] has exactly one operator,
//!   `Precedes`, and it is checked over the workflow **graph** before execution.
//!   It reads no event log, and it does not apply to the assistant loop at all
//!   — only to declared `car-workflow` stage graphs.
//!
//! So CAR statically checked properties of the plan and enforced stateless predicates on
//! each action, but never checked that *this particular run* satisfied an
//! ordering constraint (Parslee-ai/car#704).
//!
//! # Deterministic and judge-free
//!
//! Everything here is pure functions over a trace. That is the point: it is the
//! rare quality mechanism that needs no model in the loop, which matches the
//! runtime's posture — the same reason `car-verify`'s existing checks are graph
//! algorithms rather than prompts. One rule set drives two uses:
//!
//! * [`evaluate_trace`] scores a **completed** run, e.g. from a `car-eventlog`
//!   journal, for compliance after the fact;
//! * [`check_next`] checks a **prefix** online, before a call executes, so a
//!   violating call can be blocked rather than reported afterwards. That is what
//!   makes this enforcement rather than reporting.
//!
//! The two must agree, and the asymmetry between them is deliberate: a liveness
//! rule ([`TraceRule::Eventually`]) can only be violated by a run that *ends*
//! without the obligation discharged, so a prefix can never violate it. Treating
//! it as violated online would block a call for something the run might still do.

use serde::{Deserialize, Serialize};
use std::collections::HashSet;

/// One observed step of an execution trace.
#[derive(Debug, Clone, PartialEq, Eq, Serialize, Deserialize)]
pub struct TraceStep {
    /// The tool that ran.
    pub tool: String,
    /// Whether it succeeded. Load-bearing: "deploy may not run unless `test`
    /// **succeeded** earlier" is a different rule from "unless `test` ran", and
    /// the weaker reading is satisfied by a test that ran and failed.
    pub ok: bool,
}

impl TraceStep {
    pub fn ok(tool: impl Into<String>) -> Self {
        Self {
            tool: tool.into(),
            ok: true,
        }
    }
    pub fn failed(tool: impl Into<String>) -> Self {
        Self {
            tool: tool.into(),
            ok: false,
        }
    }
}

/// A temporal rule over a trace prefix.
#[derive(Debug, Clone, PartialEq, Eq, Serialize, Deserialize)]
#[serde(tag = "kind", rename_all = "snake_case")]
pub enum TraceRule {
    /// `later` may not run unless `earlier` **succeeded** earlier in this run.
    /// ("`deploy` may not run unless `test` succeeded.")
    Precedes {
        earlier: String,
        later: String,
        #[serde(default)]
        name: Option<String>,
    },
    /// `tool` may never run in this run. The trace-level counterpart of
    /// `deny_tool`, included so one spec file can express a whole procedure.
    Never {
        tool: String,
        #[serde(default)]
        name: Option<String>,
    },
    /// Once `trigger` runs, `required` must run before the trace ends.
    /// ("Once `acquire_lease` is called, `release_lease` must follow.")
    ///
    /// A **liveness** rule: only a completed trace can violate it.
    Eventually {
        trigger: String,
        required: String,
        #[serde(default)]
        name: Option<String>,
    },
    /// After `start` runs, `forbidden` may not run until `release` runs.
    /// ("`write_file` must never follow `fetch_url` without an intervening
    /// approval.")
    Until {
        start: String,
        forbidden: String,
        release: String,
        #[serde(default)]
        name: Option<String>,
    },
}

impl TraceRule {
    /// The rule's label, or a derived one so a violation is always attributable.
    pub fn label(&self) -> String {
        match self {
            Self::Precedes {
                earlier,
                later,
                name,
            } => name
                .clone()
                .unwrap_or_else(|| format!("{earlier}_precedes_{later}")),
            Self::Never { tool, name } => name.clone().unwrap_or_else(|| format!("never_{tool}")),
            Self::Eventually {
                trigger,
                required,
                name,
            } => name
                .clone()
                .unwrap_or_else(|| format!("{trigger}_eventually_{required}")),
            Self::Until {
                start,
                forbidden,
                release,
                name,
            } => name
                .clone()
                .unwrap_or_else(|| format!("{forbidden}_forbidden_between_{start}_and_{release}")),
        }
    }
}

/// A rule violated by a trace or by the call about to run.
#[derive(Debug, Clone, PartialEq, Eq, Serialize, Deserialize)]
pub struct TraceViolation {
    pub rule: String,
    /// The tool whose execution violates (or would violate) the rule.
    pub tool: String,
    /// Index into the trace, or the prefix length for an online check — i.e.
    /// the position the offending call occupies.
    pub step: usize,
    pub explanation: String,
}

/// The result of scoring a completed trace.
#[derive(Debug, Clone, PartialEq, Eq, Serialize, Deserialize)]
pub struct TraceReport {
    pub compliant: bool,
    pub violations: Vec<TraceViolation>,
    /// Steps examined, so a caller can tell "compliant" from "nothing ran".
    pub steps: usize,
}

impl TraceReport {
    /// What kind of check produced these violations — see
    /// [`crate::EvidenceTier`].
    ///
    /// Each rule is a bounded temporal predicate over a finite, fully-supplied
    /// sequence of steps, evaluated by scanning it: `Precedes` and `Until` are
    /// safety properties decided at the offending index, `Never` is membership,
    /// `Eventually` is discharge-by-end-of-trace. No search, no abstraction, no
    /// threshold — this is the crate's one *runtime* verifier, and it is as
    /// decided as the static ones.
    ///
    /// It decides compliance of **the trace it was given**. A run whose events
    /// never reached the log is not a compliant run; it is an unexamined one,
    /// which is what [`Self::steps`] is there to expose.
    pub const fn evidence_tier(&self) -> crate::EvidenceTier {
        crate::EvidenceTier::DecisionProcedure
    }
}

/// Whether `prefix` has a successful run of `tool`.
fn succeeded_in(prefix: &[TraceStep], tool: &str) -> bool {
    prefix.iter().any(|s| s.tool == tool && s.ok)
}

/// Whether `tool` appears at all (successfully or not).
fn appears_in(prefix: &[TraceStep], tool: &str) -> bool {
    prefix.iter().any(|s| s.tool == tool)
}

/// Violations that running `next` would introduce, given everything already
/// executed in `prefix`.
///
/// This is the online gate: call it *before* dispatching, and a non-empty result
/// means the call breaks the procedure. Only safety rules can be decided from a
/// prefix — see the module docs on why `Eventually` is deliberately absent here.
pub fn check_next(rules: &[TraceRule], prefix: &[TraceStep], next: &str) -> Vec<TraceViolation> {
    let step = prefix.len();
    let mut out = Vec::new();

    for rule in rules {
        match rule {
            TraceRule::Precedes { earlier, later, .. }
                if next == later && !succeeded_in(prefix, earlier) =>
            {
                let ran_but_failed = appears_in(prefix, earlier);
                out.push(TraceViolation {
                    rule: rule.label(),
                    tool: next.to_string(),
                    step,
                    explanation: if ran_but_failed {
                        format!("`{next}` requires `{earlier}` to have succeeded first; it ran and failed")
                    } else {
                        format!("`{next}` requires `{earlier}` to have succeeded first; it has not run")
                    },
                });
            }
            TraceRule::Never { tool, .. } if next == tool => {
                out.push(TraceViolation {
                    rule: rule.label(),
                    tool: next.to_string(),
                    step,
                    explanation: format!("`{next}` may never run"),
                });
            }
            TraceRule::Until {
                start,
                forbidden,
                release,
                ..
            } if next == forbidden && in_forbidden_window(prefix, start, release) => {
                out.push(TraceViolation {
                    rule: rule.label(),
                    tool: next.to_string(),
                    step,
                    explanation: format!(
                        "`{next}` may not run after `{start}` until `{release}` has run"
                    ),
                });
            }
            // `Eventually` is liveness: a prefix cannot violate it, because the
            // run may still discharge the obligation. Judged by `evaluate_trace`.
            _ => {}
        }
    }
    out
}

/// Whether the prefix currently sits inside a `start`…`release` window: `start`
/// has run more recently than any `release`.
fn in_forbidden_window(prefix: &[TraceStep], start: &str, release: &str) -> bool {
    let last = |tool: &str| prefix.iter().rposition(|s| s.tool == tool && s.ok);
    match (last(start), last(release)) {
        (Some(s), Some(r)) => s > r,
        (Some(_), None) => true,
        (None, _) => false,
    }
}

/// Score a **completed** trace against the rules.
///
/// Replays the trace through the same online check so the two can never
/// disagree about a safety rule, then adds the liveness rules that only a
/// finished run can settle.
pub fn evaluate_trace(rules: &[TraceRule], trace: &[TraceStep]) -> TraceReport {
    let mut violations = Vec::new();

    for (i, step) in trace.iter().enumerate() {
        violations.extend(check_next(rules, &trace[..i], &step.tool));
    }

    // Liveness: an obligation triggered but never discharged.
    for rule in rules {
        if let TraceRule::Eventually {
            trigger, required, ..
        } = rule
        {
            let triggered_at: Vec<usize> = trace
                .iter()
                .enumerate()
                .filter(|(_, s)| &s.tool == trigger && s.ok)
                .map(|(i, _)| i)
                .collect();
            for at in triggered_at {
                let discharged = trace[at + 1..].iter().any(|s| &s.tool == required && s.ok);
                if !discharged {
                    violations.push(TraceViolation {
                        rule: rule.label(),
                        tool: trigger.clone(),
                        step: at,
                        explanation: format!(
                            "`{trigger}` ran at step {at} but `{required}` never followed"
                        ),
                    });
                }
            }
        }
    }

    TraceReport {
        compliant: violations.is_empty(),
        steps: trace.len(),
        violations,
    }
}

/// Build a trace from `car-eventlog` JSONL records.
///
/// Takes parsed JSON rather than `car_eventlog::Event` deliberately: `car-verify`
/// depends only on `car-ir` and serde, and making the verifier depend on the
/// logger would invert the layering for no gain — the journal is already JSON,
/// and one field access is cheaper than a crate edge.
///
/// Only `action_succeeded` / `action_failed` become steps; every other kind is
/// bookkeeping about a call rather than the call itself, and counting
/// `action_executing` too would double every step. The tool name is read from
/// `data.tool`, falling back to `action_id` — the coder journals a tool call
/// under `data.tool` and its checks under an `action_id` of `check:<name>`.
pub fn trace_from_events(events: &[serde_json::Value]) -> Vec<TraceStep> {
    events
        .iter()
        .filter_map(|e| {
            let kind = e.get("kind")?.as_str()?;
            let ok = match kind {
                "action_succeeded" => true,
                "action_failed" => false,
                _ => return None,
            };
            let tool = e
                .get("data")
                .and_then(|d| d.get("tool"))
                .and_then(|t| t.as_str())
                .or_else(|| e.get("action_id").and_then(|a| a.as_str()))?
                .to_string();
            Some(TraceStep { tool, ok })
        })
        .collect()
}

/// Tools named by any rule — the set a dispatcher needs to watch, so a runtime
/// can skip the check entirely for calls no rule mentions.
pub fn governed_tools(rules: &[TraceRule]) -> HashSet<String> {
    let mut out = HashSet::new();
    for rule in rules {
        match rule {
            TraceRule::Precedes { earlier, later, .. } => {
                out.insert(earlier.clone());
                out.insert(later.clone());
            }
            TraceRule::Never { tool, .. } => {
                out.insert(tool.clone());
            }
            TraceRule::Eventually {
                trigger, required, ..
            } => {
                out.insert(trigger.clone());
                out.insert(required.clone());
            }
            TraceRule::Until {
                start,
                forbidden,
                release,
                ..
            } => {
                out.insert(start.clone());
                out.insert(forbidden.clone());
                out.insert(release.clone());
            }
        }
    }
    out
}

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

    fn precedes(earlier: &str, later: &str) -> TraceRule {
        TraceRule::Precedes {
            earlier: earlier.into(),
            later: later.into(),
            name: None,
        }
    }

    // --- Precedes: "deploy may not run unless test succeeded" -------------

    #[test]
    fn deploy_without_test_is_blocked_online_and_offline() {
        let rules = [precedes("test", "deploy")];
        let prefix = [TraceStep::ok("build")];
        let online = check_next(&rules, &prefix, "deploy");
        assert_eq!(online.len(), 1, "{online:?}");
        assert!(online[0].explanation.contains("has not run"));

        let report = evaluate_trace(&rules, &[TraceStep::ok("build"), TraceStep::ok("deploy")]);
        assert!(!report.compliant);
        assert_eq!(report.violations.len(), 1);
    }

    #[test]
    fn deploy_after_a_successful_test_is_allowed() {
        let rules = [precedes("test", "deploy")];
        let trace = [TraceStep::ok("test"), TraceStep::ok("deploy")];
        assert!(check_next(&rules, &trace[..1], "deploy").is_empty());
        assert!(evaluate_trace(&rules, &trace).compliant);
    }

    /// The distinction the `ok` flag exists for: a test that RAN is not a test
    /// that PASSED, and the weaker reading would authorize the deploy.
    #[test]
    fn a_failed_test_does_not_authorize_the_deploy() {
        let rules = [precedes("test", "deploy")];
        let prefix = [TraceStep::failed("test")];
        let v = check_next(&rules, &prefix, "deploy");
        assert_eq!(v.len(), 1);
        assert!(
            v[0].explanation.contains("ran and failed"),
            "the message must distinguish this from never having run: {:?}",
            v[0].explanation
        );
    }

    #[test]
    fn an_unrelated_tool_is_never_blocked() {
        let rules = [precedes("test", "deploy")];
        assert!(check_next(&rules, &[], "format").is_empty());
    }

    // --- Never ------------------------------------------------------------

    #[test]
    fn never_blocks_on_the_first_call() {
        let rules = [TraceRule::Never {
            tool: "rm_rf".into(),
            name: None,
        }];
        assert_eq!(check_next(&rules, &[], "rm_rf").len(), 1);
        assert!(!evaluate_trace(&rules, &[TraceStep::ok("rm_rf")]).compliant);
    }

    // --- Eventually: liveness ---------------------------------------------

    #[test]
    fn an_undischarged_obligation_fails_the_completed_trace() {
        let rules = [TraceRule::Eventually {
            trigger: "acquire_lease".into(),
            required: "release_lease".into(),
            name: None,
        }];
        let report = evaluate_trace(&rules, &[TraceStep::ok("acquire_lease")]);
        assert!(!report.compliant);
        assert!(report.violations[0].explanation.contains("never followed"));
    }

    #[test]
    fn a_discharged_obligation_passes() {
        let rules = [TraceRule::Eventually {
            trigger: "acquire_lease".into(),
            required: "release_lease".into(),
            name: None,
        }];
        let trace = [
            TraceStep::ok("acquire_lease"),
            TraceStep::ok("write_file"),
            TraceStep::ok("release_lease"),
        ];
        assert!(evaluate_trace(&rules, &trace).compliant);
    }

    /// The deliberate asymmetry: a prefix can never violate liveness, or the
    /// gate would block a call for something the run might still do.
    #[test]
    fn liveness_never_blocks_a_prefix() {
        let rules = [TraceRule::Eventually {
            trigger: "acquire_lease".into(),
            required: "release_lease".into(),
            name: None,
        }];
        let prefix = [TraceStep::ok("acquire_lease")];
        assert!(check_next(&rules, &prefix, "anything").is_empty());
    }

    /// Each trigger carries its own obligation — a single release does not
    /// discharge a lease acquired after it.
    #[test]
    fn a_second_trigger_needs_its_own_discharge() {
        let rules = [TraceRule::Eventually {
            trigger: "acquire_lease".into(),
            required: "release_lease".into(),
            name: None,
        }];
        let trace = [
            TraceStep::ok("acquire_lease"),
            TraceStep::ok("release_lease"),
            TraceStep::ok("acquire_lease"),
        ];
        let report = evaluate_trace(&rules, &trace);
        assert!(!report.compliant);
        assert_eq!(report.violations[0].step, 2);
    }

    // --- Until: scoped prohibition ----------------------------------------

    fn until_rule() -> TraceRule {
        TraceRule::Until {
            start: "fetch_url".into(),
            forbidden: "write_file".into(),
            release: "approval".into(),
            name: None,
        }
    }

    #[test]
    fn the_window_opens_at_start_and_closes_at_release() {
        let rules = [until_rule()];
        // Before `fetch_url` the write is fine.
        assert!(check_next(&rules, &[], "write_file").is_empty());
        // Inside the window it is not.
        let inside = [TraceStep::ok("fetch_url")];
        assert_eq!(check_next(&rules, &inside, "write_file").len(), 1);
        // After the release it is fine again.
        let released = [TraceStep::ok("fetch_url"), TraceStep::ok("approval")];
        assert!(check_next(&rules, &released, "write_file").is_empty());
    }

    /// A second `fetch_url` after an approval re-opens the window — otherwise
    /// one approval would authorize every later fetch for the rest of the run.
    #[test]
    fn a_later_start_reopens_the_window() {
        let rules = [until_rule()];
        let prefix = [
            TraceStep::ok("fetch_url"),
            TraceStep::ok("approval"),
            TraceStep::ok("fetch_url"),
        ];
        assert_eq!(check_next(&rules, &prefix, "write_file").len(), 1);
    }

    /// A failed approval does not close the window.
    #[test]
    fn a_failed_release_does_not_close_the_window() {
        let rules = [until_rule()];
        let prefix = [TraceStep::ok("fetch_url"), TraceStep::failed("approval")];
        assert_eq!(check_next(&rules, &prefix, "write_file").len(), 1);
    }

    // --- Agreement between the two entry points ---------------------------

    /// Offline scoring replays the online check, so a safety rule can never be
    /// enforced one way live and scored another way afterwards.
    #[test]
    fn offline_scoring_agrees_with_the_online_gate() {
        let rules = [precedes("test", "deploy"), until_rule()];
        let trace = [
            TraceStep::ok("fetch_url"),
            TraceStep::ok("write_file"), // violates Until
            TraceStep::ok("deploy"),     // violates Precedes
        ];
        let report = evaluate_trace(&rules, &trace);
        assert_eq!(report.violations.len(), 2, "{report:?}");
        assert_eq!(report.steps, 3);

        // The same two calls are refused online, at the same positions.
        assert_eq!(check_next(&rules, &trace[..1], "write_file").len(), 1);
        assert_eq!(check_next(&rules, &trace[..2], "deploy").len(), 1);
    }

    #[test]
    fn an_empty_rule_set_is_vacuously_compliant() {
        let report = evaluate_trace(&[], &[TraceStep::ok("anything")]);
        assert!(report.compliant);
        assert_eq!(report.steps, 1);
    }

    #[test]
    fn governed_tools_lists_every_tool_a_rule_mentions() {
        let rules = [precedes("test", "deploy"), until_rule()];
        let tools = governed_tools(&rules);
        for expected in ["test", "deploy", "fetch_url", "write_file", "approval"] {
            assert!(
                tools.contains(expected),
                "{expected} missing from {tools:?}"
            );
        }
    }

    #[test]
    fn a_trace_is_built_from_event_log_records() {
        let events: Vec<serde_json::Value> = vec![
            serde_json::json!({"kind": "action_executing", "data": {"tool": "test"}}),
            serde_json::json!({"kind": "action_succeeded", "data": {"tool": "test"}}),
            serde_json::json!({"kind": "action_failed", "data": {"tool": "deploy"}}),
            serde_json::json!({"kind": "state_changed", "data": {}}),
            serde_json::json!({"kind": "action_succeeded", "action_id": "check:lint"}),
        ];
        let trace = trace_from_events(&events);
        assert_eq!(
            trace,
            vec![
                TraceStep::ok("test"),
                TraceStep::failed("deploy"),
                TraceStep::ok("check:lint"),
            ],
            "only executed calls become steps, and `action_executing` must not \
             double-count the call its `action_succeeded` already records"
        );
    }

    /// End-to-end for the acceptance criterion: a rule is authored, a run is
    /// replayed from its journal, and the violation is detected.
    #[test]
    fn a_violating_run_is_detected_from_its_event_log() {
        let rules = [precedes("test", "deploy")];
        let events: Vec<serde_json::Value> = vec![
            serde_json::json!({"kind": "action_succeeded", "data": {"tool": "build"}}),
            serde_json::json!({"kind": "action_succeeded", "data": {"tool": "deploy"}}),
        ];
        let report = evaluate_trace(&rules, &trace_from_events(&events));
        assert!(!report.compliant);
        assert_eq!(report.violations[0].tool, "deploy");
    }

    #[test]
    fn rules_round_trip_through_json() {
        let rules = vec![precedes("test", "deploy"), until_rule()];
        let json = serde_json::to_string(&rules).unwrap();
        let back: Vec<TraceRule> = serde_json::from_str(&json).unwrap();
        assert_eq!(rules, back);
    }
}

/// A live gate: accumulates the run's trace and refuses a call that would break
/// the procedure.
///
/// This is the piece that makes trace rules *enforcement* rather than reporting.
/// `car-policy`'s three rule kinds are stateless, so they can be registered as
/// `PolicyCheck`s that see one action in isolation; a temporal rule cannot —
/// it needs the prefix. Hence a gate object the dispatcher owns for the life of
/// the run.
///
/// Empty rules make every method a no-op, which is the overwhelmingly common
/// case: a project with no `trace_rule` entries behaves exactly as before.
#[derive(Debug, Clone, Default)]
pub struct TraceGate {
    rules: Vec<TraceRule>,
    trace: Vec<TraceStep>,
    governed: HashSet<String>,
}

impl TraceGate {
    pub fn new(rules: Vec<TraceRule>) -> Self {
        let governed = governed_tools(&rules);
        Self {
            rules,
            trace: Vec::new(),
            governed,
        }
    }

    /// True when no rule was authored — callers can skip the gate entirely.
    pub fn is_empty(&self) -> bool {
        self.rules.is_empty()
    }

    /// Check a call **before** dispatching it. Empty result = allowed.
    ///
    /// Short-circuits on tools no rule mentions, so the cost on an ungoverned
    /// call is one hash lookup.
    pub fn check(&self, tool: &str) -> Vec<TraceViolation> {
        if self.rules.is_empty() || !self.governed.contains(tool) {
            return Vec::new();
        }
        check_next(&self.rules, &self.trace, tool)
    }

    /// Record that `tool` ran. Call this for every executed tool, including
    /// ungoverned ones: a rule added later in the session is not the concern,
    /// but `Until` windows and `Precedes` both depend on ordering, and a trace
    /// with holes in it silently answers the wrong question.
    pub fn record(&mut self, tool: &str, ok: bool) {
        self.trace.push(TraceStep {
            tool: tool.to_string(),
            ok,
        });
    }

    /// Score the completed run, including the liveness rules a prefix cannot
    /// settle. Call at the end of a run.
    pub fn finish(&self) -> TraceReport {
        evaluate_trace(&self.rules, &self.trace)
    }

    /// The trace accumulated so far.
    pub fn trace(&self) -> &[TraceStep] {
        &self.trace
    }
}

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

    fn rules() -> Vec<TraceRule> {
        vec![
            TraceRule::Precedes {
                earlier: "test".into(),
                later: "deploy".into(),
                name: None,
            },
            TraceRule::Eventually {
                trigger: "acquire_lease".into(),
                required: "release_lease".into(),
                name: None,
            },
        ]
    }

    #[test]
    fn an_empty_gate_allows_everything() {
        let gate = TraceGate::default();
        assert!(gate.is_empty());
        assert!(gate.check("anything").is_empty());
        assert!(gate.finish().compliant);
    }

    #[test]
    fn the_gate_refuses_then_allows_as_the_run_progresses() {
        let mut gate = TraceGate::new(rules());
        assert_eq!(gate.check("deploy").len(), 1, "no test has run yet");

        gate.record("test", true);
        assert!(gate.check("deploy").is_empty(), "the precondition is met");
    }

    /// A failed run of the precondition must not unlock the gated call.
    #[test]
    fn a_failed_precondition_keeps_the_gate_shut() {
        let mut gate = TraceGate::new(rules());
        gate.record("test", false);
        assert_eq!(gate.check("deploy").len(), 1);
    }

    /// Ungoverned tools short-circuit, and are still recorded — ordering
    /// matters for `Until`, so a trace with holes answers the wrong question.
    #[test]
    fn ungoverned_tools_are_allowed_but_still_recorded() {
        let mut gate = TraceGate::new(rules());
        assert!(gate.check("read_file").is_empty());
        gate.record("read_file", true);
        assert_eq!(gate.trace().len(), 1);
    }

    /// Liveness is settled only at the end, never by the gate mid-run.
    #[test]
    fn an_undischarged_obligation_surfaces_only_at_finish() {
        let mut gate = TraceGate::new(rules());
        gate.record("acquire_lease", true);
        assert!(
            gate.check("anything").is_empty(),
            "a prefix must not block on liveness"
        );
        let report = gate.finish();
        assert!(!report.compliant, "the completed run is non-compliant");

        let mut gate = TraceGate::new(rules());
        gate.record("acquire_lease", true);
        gate.record("release_lease", true);
        assert!(gate.finish().compliant);
    }
}