lex_vcs/

attestation.rs

//! Persistent evidence about a stage (#132).
//!
//! [`Operation`](crate::Operation) records *what* changed.
//! [`Intent`](crate::Intent) records *why*. An [`Attestation`] records
//! *what we know about the result*: did this stage typecheck, did its
//! examples pass, did a spec prove it, did `lex agent-tool` run it
//! cleanly under a sandbox.
//!
//! Today every verification (`lex check`, `lex agent-tool --spec ...`,
//! `lex audit --effect ...`) runs, prints a verdict, and exits. The
//! evidence is ephemeral — there's no persistent answer to "has this
//! stage ever been spec-checked?" beyond rerunning. That makes
//! attestations useless as a CI gate and useless as a trust signal
//! across sessions.
//!
//! This module is the foundational data layer for tier-2's evidence
//! story. Producers (`lex check` emits `TypeCheck`, `lex agent-tool`
//! emits `Spec` / `Examples` / `DiffBody` / `SandboxRun`) and
//! consumers (`lex blame --with-evidence`, `GET /v1/stage/<id>/
//! attestations`) wire to it in subsequent slices.
//!
//! # Identity
//!
//! [`AttestationId`] is the lowercase-hex SHA-256 of the canonical
//! form of `(stage_id, op_id, intent_id, kind, result, produced_by)`.
//! `cost`, `timestamp`, and `signature` are deliberately *not* in the
//! hash so two independent runs of the same logical verification —
//! same stage, same kind, same producer, same outcome — produce the
//! same `attestation_id`. This is the dedup property the issue calls
//! out: harnesses can ask "has this exact verification been done?"
//! by checking for the id without rerunning.
//!
//! # Storage
//!
//! ```text
//! <root>/attestations/<AttestationId>.json
//! <root>/attestations/by-stage/<StageId>/<AttestationId>
//! ```
//!
//! The primary file under `attestations/` is the source of truth.
//! `by-stage/` is a per-stage index — empty marker files whose names
//! point at the primary record. Rebuildable from primary records on
//! demand; we write it eagerly so `lex stage <id> --attestations` is
//! a directory listing rather than a full scan.
//!
//! `by-spec/` (mentioned in the issue) is deferred until a producer
//! actually emits `Spec` attestations against persisted spec ids.
//!
//! # Trust model
//!
//! Attestations are claims, not proofs. The store doesn't trust
//! attestations from outside — it just stores them. A maintainer
//! choosing to skip CI for a stage that already has a passing spec
//! attestation from a known producer is a *policy* decision, not a
//! guarantee the store enforces. The optional Ed25519 signature
//! field exists so an attestation can be cryptographically tied to
//! a producer (e.g. a CI runner's public key) and the policy
//! decision auditable. Verifying signatures is out of scope for the
//! data layer.

use serde::{Deserialize, Serialize};
use std::collections::BTreeSet;
use std::fs;
use std::io::{self, Write};
use std::path::{Path, PathBuf};
use std::time::{SystemTime, UNIX_EPOCH};

use crate::canonical;
use crate::intent::IntentId;
use crate::operation::{OpId, StageId};

/// Content-addressed identity of an attestation. Lowercase-hex
/// SHA-256 of the canonical form of
/// `(stage_id, op_id, intent_id, kind, result, produced_by)`.
pub type AttestationId = String;

/// Reference to a spec file. Free-form string so callers can use
/// either a content hash or a logical name; the data layer doesn't
/// care which. Producers should pick one and stick with it for
/// dedup to work as expected.
pub type SpecId = String;

/// Content hash of a file (examples list, body source, etc.). Kept
/// as a string for the same reason as [`OpId`]: we want this crate
/// to have no view into the hash function used by callers.
pub type ContentHash = String;

/// The decision a [`AttestationKind::Review`] carries (#836 G4).
#[derive(Debug, Clone, PartialEq, Eq, Serialize, Deserialize)]
#[serde(rename_all = "snake_case")]
pub enum ReviewVerdict {
    /// This candidate should win / this stage is good to promote.
    Approve,
    /// This candidate should not win / this stage should not advance.
    Reject,
    /// Not a veto, but changes are wanted before it advances.
    RequestChanges,
}

/// What was verified. The variants mirror the verdict surfaces
/// `lex agent-tool` and the store-write gate already produce.
#[derive(Debug, Clone, PartialEq, Eq, Serialize, Deserialize)]
#[serde(tag = "kind", rename_all = "snake_case")]
pub enum AttestationKind {
    /// `lex agent-tool --examples FILE` — body was run against
    /// `{input, expected}` pairs.
    Examples {
        file_hash: ContentHash,
        count: usize,
    },
    /// `lex spec check` or `lex agent-tool --spec FILE` — a
    /// behavioral contract was checked against the body.
    Spec {
        spec_id: SpecId,
        method: SpecMethod,
        #[serde(default, skip_serializing_if = "Option::is_none")]
        trials: Option<usize>,
    },
    /// `lex agent-tool --diff-body 'src'` — a second body was run on
    /// the same inputs and the outputs compared.
    DiffBody {
        other_body_hash: ContentHash,
        input_count: usize,
    },
    /// A structured review verdict on a stage — closes the
    /// Candidate->Promote gap (#836 G4): the path from a `Candidate`
    /// to a `Promote` otherwise carries no recorded reason. An agent
    /// or human records why a candidate should (or shouldn't) win the
    /// bake-off, addressable at the candidate's stage like any other
    /// attestation. `Approve`/`Reject`/`RequestChanges` also map onto
    /// the `result` field (Passed/Failed/Inconclusive) so existing
    /// result-based tooling reads it sensibly.
    Review {
        reviewer: String,
        verdict: ReviewVerdict,
        #[serde(default, skip_serializing_if = "Option::is_none")]
        notes: Option<String>,
    },
    /// Emitted by the store-write gate (#130) on every accepted op.
    /// The store can answer "the HEAD typechecks" as a queryable
    /// fact rather than an implicit invariant.
    TypeCheck,
    /// Emitted by `lex audit --effect K` when no violations are
    /// found. Useful as a trust signal that a stage was checked
    /// against a specific effect-policy revision.
    EffectAudit,
    /// Emitted by `lex agent-tool` on a successful sandboxed run.
    /// `effects` is the set the sandbox actually allowed; useful for
    /// answering "did this code run under fs_write?" after the fact.
    SandboxRun {
        effects: BTreeSet<String>,
    },
    /// Human-issued override (lex-tea v3, #172). Records that a
    /// human took an action that bypassed an automatic verdict
    /// — e.g. activating a stage despite a `Spec::Failed` or
    /// `TypeCheck::Failed` attestation. Subject to the same
    /// trust trail as agent attestations: the audit fact lives
    /// in the log alongside what it overrode.
    ///
    /// `actor` is the human's identifier (today: `LEX_TEA_USER`
    /// env var or `--actor` flag; v3b adds session auth).
    /// `target_attestation_id` points at the attestation being
    /// overridden, when one exists; for unconditional pins
    /// (e.g. activate-by-default) it can be `None`.
    Override {
        actor: String,
        reason: String,
        #[serde(default, skip_serializing_if = "Option::is_none")]
        target_attestation_id: Option<AttestationId>,
    },
    /// `lex stage defer` (lex-tea v3b, #172). Records that a human
    /// looked at the stage and chose to revisit it later. No state
    /// change — purely an audit/triage signal so dashboards and AI
    /// reviewers can see "this isn't abandoned, it's snoozed."
    Defer {
        actor: String,
        reason: String,
    },
    /// `lex stage block` (lex-tea v3b, #172). Records that a human
    /// has decided this stage should not activate. `lex stage pin`
    /// and any other activation path consults the attestation log
    /// and refuses while a Block is the latest decision for the
    /// stage. Reversed by [`AttestationKind::Unblock`].
    Block {
        actor: String,
        reason: String,
    },
    /// `lex stage unblock` (lex-tea v3b, #172). Counterpart to
    /// [`AttestationKind::Block`]. The attestation log is append-
    /// only, so we encode "block lifted" as a separate, later fact
    /// rather than mutating the original block.
    Unblock {
        actor: String,
        reason: String,
    },
    /// `lex run --trace` finalized a [`lex_trace::TraceTree`] (#246).
    /// Links the trace blob to the stage that was the run's entry
    /// point. The trace itself stays at
    /// `<store>/traces/<run_id>/trace.json` (per
    /// `docs/design/trace-vs-vcs.md`); this attestation is the
    /// audit-side hook so `lex attest filter --kind trace` and
    /// cross-store sync can reason about runs without copying the
    /// trace bytes.
    ///
    /// `root_target` is the entry function's `SigId` — the call site
    /// the user (or agent) typed on the command line. Distinct from
    /// `Attestation::stage_id`, which records the *content-addressed*
    /// stage the entry function resolved to; the same `root_target`
    /// across multiple body edits surfaces as multiple
    /// `(stage_id, root_target)` rows in the attestation log.
    Trace {
        run_id: TraceRunId,
        root_target: super::operation::SigId,
    },
    /// Retroactive producer quarantine (#248). Declares "as of
    /// `blocked_at`, attestations produced by `tool_id` are no
    /// longer trusted; the branch advance gate must refuse to move
    /// past any op whose attestations were produced by this tool
    /// at or after `blocked_at`."
    ///
    /// Distinct from `policy.json`'s `blocked_producers` (#181):
    /// that is a *forward-going* read-time tag for the activity
    /// feed; this is a write-time gate on branch advance, retro-
    /// active to a specific timestamp. The two compose cleanly —
    /// `blocked_producers` filters what reviewers see; `ProducerBlock`
    /// stops a compromised tool's history from being promoted past
    /// a known-bad point.
    ///
    /// Stored at the attestation log under `stage_id == tool_id`
    /// so the by-stage index doubles as a by-tool lookup for these
    /// records — no schema break, no separate index needed.
    /// `Attestation::stage_id` carries the `tool_id` for these
    /// records; the variant payload duplicates it for clarity in
    /// the JSON.
    ProducerBlock {
        tool_id: String,
        reason: String,
        blocked_at: u64,
    },
    /// Counterpart to [`AttestationKind::ProducerBlock`] (#248). The
    /// attestation log is append-only, so revoking a producer block
    /// is a separate, later fact rather than a delete. The branch
    /// advance gate honors the most recent verdict for each
    /// `tool_id` by timestamp.
    ProducerUnblock {
        tool_id: String,
        reason: String,
        unblocked_at: u64,
    },
    /// Auto-emitted by `Store::apply_operation_checked` when an op
    /// is rejected for `TypeError` (#281). Records the failed op's
    /// id, the structured type-error envelope, and an optional
    /// suggested-transform payload (left empty by the gate; the
    /// `lex repair --apply` flow populates it via LLM call). The
    /// hint is attached to the candidate stage that didn't
    /// typecheck, so `lex_vcs::AttestationLog::list_for_stage`
    /// surfaces it on the next read.
    ///
    /// Schema: `errors` and `suggested_transform` are
    /// `serde_json::Value` to keep this crate independent of
    /// `lex-types::TypeError` (which lives downstream) and to let
    /// the slice-2 LLM integration ship without a schema bump.
    RepairHint {
        failed_op_id: super::operation::OpId,
        errors: serde_json::Value,
        #[serde(default, skip_serializing_if = "Option::is_none")]
        suggested_transform: Option<serde_json::Value>,
    },
    /// Records one iteration of `lex repair --apply` (#281). The
    /// repair loop emits a chain of `RepairAttempt`s — one per
    /// applied transform — so the audit trail walks the agent's
    /// fix progression.
    RepairAttempt {
        hint_id: super::operation::OpId,
        /// Outcome tag: `passed` / `failed` / `skipped`.
        outcome: String,
        #[serde(default, skip_serializing_if = "Option::is_none")]
        applied_op_id: Option<super::operation::OpId>,
    },
    /// Positive trust signal for a producer (#293). Complement to
    /// [`Self::ProducerBlock`]. Computed from a producer's recent
    /// history of (passed, failed, inconclusive) attestations;
    /// not manually set. `score_thousandths` is in `[0, 1000]`
    /// (representing `0.0 .. 1.0`); fixed-point because
    /// `AttestationKind` is `Eq` for content-addressed hashing,
    /// which `f64` doesn't implement. Consumers (the
    /// `required_attestations` gate) may waive a requirement
    /// when the latest score for a tool exceeds a configured
    /// threshold in `policy.required_attestations[].skip_if_producer_trust_thousandths_above`.
    ///
    /// Refuses to grant trust to a tool with an active
    /// `ProducerBlock` (the hard veto wins).
    ///
    /// Stored under `stage_id == tool_id` so the by-stage index
    /// doubles as a per-tool lookup — same trick `ProducerBlock`
    /// uses.
    ProducerTrust {
        tool_id: String,
        /// Score × 1000, clamped to `[0, 1000]`. Derived from
        /// `passed / (passed + failed + inconclusive)` over the
        /// last `window` attestations from this tool.
        score_thousandths: u32,
        /// Free-form reference to the evidence corpus the score
        /// was derived from — e.g. "window=1000 as of <head_op>".
        evidence: String,
        granted_by: String,
    },
    /// Records that the `required_attestations` gate waived a
    /// requirement because the producer's `ProducerTrust` score
    /// exceeded the configured threshold (#293). Audit signal —
    /// not load-bearing for gate decisions, but ensures every
    /// skip is recoverable from the attestation log.
    TrustWaived {
        /// Tool whose trust score caused the waiver.
        producer: String,
        /// Latest score (× 1000) consulted at gate time.
        score_thousandths: u32,
        /// Threshold (× 1000) from the policy rule.
        threshold_thousandths: u32,
        /// Which required-attestation kind tag was skipped
        /// (e.g. `spec`, `type_check`).
        kind_tag: String,
    },
    /// A capsule installed cleanly under lex-os (lex-os#36 / #38).
    /// Promotes the tamper-evident `CapsuleInstalled` record from a
    /// `lex-os capsule install --audit-out` log into a durable,
    /// content-addressed attestation, via `lex attest import-install`.
    ///
    /// In the capsule distribution model the publisher's signing key
    /// *is* the producer identity, so these records are stored under
    /// `stage_id == signer` **and** carry `produced_by.tool == signer`
    /// — the same convention `ProducerBlock` / `ProducerTrust` use.
    /// That makes a publisher's install track record feed
    /// `recompute_producer_trust` (which scores `produced_by.tool`)
    /// and, through it, the trusted-keys keyring that `capsule install
    /// --trusted-keys` consumes. The loop closes: install → attestation
    /// → earned trust → keyring → next install.
    CapsuleInstall {
        /// `name@version` label of the installed artifact.
        artifact: String,
        /// Hex SHA-256 of the published archive bytes — the
        /// publish-time identity of exactly which bytes installed.
        /// Empty when imported from a pre-content-hash audit log.
        content_hash: ContentHash,
        /// The publisher's Ed25519 public key (hex): the verified
        /// signer of the capability contract. Duplicated from
        /// `stage_id` / `produced_by.tool` for clarity in the JSON.
        signer: String,
        /// The grant the box actually ran at — `meet(consumer,
        /// requires)`, pretty-printed.
        effective_grant: String,
    },
    /// A plan-shaped decision a capability gate reached, promoted into
    /// durable evidence by `lex attest import-apply` (#790).
    ///
    /// Two gates emit this fact today — `lex-iac` between `terraform
    /// plan` and `terraform apply`, and `lex-k8s` at Kubernetes
    /// admission — and both emit the *same* fact: a plan-shaped
    /// artifact, checked against a manifest, decided under a signer.
    /// The name is deliberately generic. An `InfraApply` variant would
    /// have pushed the Kubernetes gate into minting a near-duplicate,
    /// and a duplicate discriminant splits one producer's track record
    /// across two kinds. Whatever differs between the gates lives in
    /// the `gate` and `subject` fields, which are payload rather than
    /// identity-by-variant.
    ///
    /// Stored under `stage_id == signer` **and** `produced_by.tool ==
    /// signer`, the convention [`Self::CapsuleInstall`] /
    /// [`Self::ProducerBlock`] / [`Self::ProducerTrust`] use — get it
    /// wrong and `recompute_producer_trust`, which scores
    /// `produced_by.tool`, silently never sees these records.
    ///
    /// # Refusals are part of the record
    ///
    /// [`AttestationResult`] carries the verdict, so a refused decision
    /// is this same kind with `Failed { detail }`. That is not an
    /// afterthought: producer trust is `passed / (passed + failed)`, so
    /// a corpus of acceptances only would score every submitter 1.0 and
    /// mean nothing. A submitter loses trust by having its refusals on
    /// the record next to its acceptances.
    PlanApply {
        /// Which gate decided — `terraform`, `kubernetes`, … Free-form,
        /// and in the payload rather than the discriminant so a third
        /// gate needs no schema change here.
        gate: String,
        /// What was decided about, in the gate's own vocabulary: a
        /// workspace, a namespaced pod name. Human-facing; may be empty
        /// when the gate names nothing.
        subject: String,
        /// Hex SHA-256 of the artifact's bytes — the plan or spec the
        /// decision was actually reached about. Load-bearing: an
        /// acceptance authorises *these* bytes, so a substituted plan
        /// must not match. Never empty; the importer refuses an event
        /// without it rather than minting evidence that matches
        /// anything.
        artifact_sha256: ContentHash,
        /// The identity the decision was made under — a CI pipeline
        /// key, a ServiceAccount, an agent key. Duplicated from
        /// `stage_id` / `produced_by.tool` for clarity in the JSON.
        signer: String,
        /// The manifest the artifact was checked against: the ceiling
        /// in force at decision time.
        manifest: String,
    },
    /// Replay-as-verification (#836 G3): the recorded [`Intent`] behind
    /// an op was re-run against the op's parent state, and the
    /// regenerated stage compared to the recorded one. Makes the
    /// reproducibility claim concrete — "can this change be regenerated
    /// from its recorded cause". Addressed to the op's recorded stage;
    /// `result` maps `reproduced` onto Passed/Failed so result-based
    /// tooling reads it. The model call itself is external (the agent
    /// harness regenerates and hands back a candidate); this attestation
    /// records the deterministic comparison lex performed.
    ///
    /// [`Intent`]: crate::Intent
    Replay {
        /// The stage id the op recorded producing — what a faithful
        /// regeneration should reproduce.
        expected_stage_id: super::operation::StageId,
        /// The stage id the regeneration actually produced, or `None`
        /// when the regenerator returned nothing / a non-matching sig.
        #[serde(default, skip_serializing_if = "Option::is_none")]
        produced_stage_id: Option<super::operation::StageId>,
        /// Whether the regeneration reproduced the recorded change — by
        /// exact stage-id match, or (see `behavioral_samples`) behaviorally.
        reproduced: bool,
        /// When reproduction was established *behaviorally* rather than by
        /// exact stage-id match — the regenerated function returned the same
        /// value as the recorded one over this many sampled inputs (#836
        /// follow-up). `None` for an exact match (the stronger claim:
        /// `produced_stage_id == expected_stage_id`) or a genuine miss.
        /// Distinguishes "the same function, written differently" from
        /// "byte-identical" without conflating them.
        #[serde(default, skip_serializing_if = "Option::is_none")]
        behavioral_samples: Option<usize>,
        /// The model the recorded intent named, for audit (`None` when
        /// the op carried no intent or the intent no model).
        #[serde(default, skip_serializing_if = "Option::is_none")]
        model: Option<String>,
    },
}

/// Walk a tool's `ProducerBlock` / `ProducerUnblock` attestations
/// and return the active block timestamp, if any (#248). The
/// attestation log is append-only, so a tool's state is whichever
/// `ProducerBlock` / `ProducerUnblock` record has the latest
/// `timestamp`. Returns `Some(blocked_at)` when the latest verdict
/// is a `ProducerBlock` and `None` when the latest is an unblock or
/// no verdict exists.
///
/// Ties: a `ProducerUnblock` at the same wall-clock second as a
/// `ProducerBlock` wins, so re-running an unblock immediately after
/// a block leaves the tool unblocked. Mirrors the tie-breaking in
/// [`is_stage_blocked`].
pub fn active_producer_block(
    attestations: &[Attestation],
    tool_id: &str,
) -> Option<u64> {
    let mut latest: Option<&Attestation> = None;
    for a in attestations {
        let matches = match &a.kind {
            AttestationKind::ProducerBlock { tool_id: tid, .. }
            | AttestationKind::ProducerUnblock { tool_id: tid, .. } => tid == tool_id,
            _ => false,
        };
        if !matches {
            continue;
        }
        match latest {
            None => latest = Some(a),
            Some(prev) if a.timestamp > prev.timestamp => latest = Some(a),
            Some(prev) if a.timestamp == prev.timestamp
                && matches!(a.kind, AttestationKind::ProducerUnblock { .. }) =>
            {
                latest = Some(a);
            }
            _ => {}
        }
    }
    match latest.map(|a| &a.kind) {
        Some(AttestationKind::ProducerBlock { blocked_at, .. }) => Some(*blocked_at),
        _ => None,
    }
}

/// Stable identifier for a [`lex_trace::TraceTree`]. Mirrors the
/// `run_id` field on the trace JSON; kept as a `String` so this
/// crate doesn't pull `lex-trace` in.
pub type TraceRunId = String;

/// Walk a stage's attestations and return whether the latest
/// Block/Unblock decision is currently a Block. Used by
/// activation paths (e.g. `lex stage pin`) to refuse when a
/// human has signalled the stage shouldn't ship.
///
/// "Latest" is defined by `timestamp`, which matches what users
/// see in `lex stage <id> --attestations`. Ties go to Unblock so
/// retrying an unblock right after a block (same wall-clock
/// second) doesn't leave the stage stuck.
pub fn is_stage_blocked(attestations: &[Attestation]) -> bool {
    let mut latest: Option<&Attestation> = None;
    for a in attestations {
        if !matches!(a.kind, AttestationKind::Block { .. } | AttestationKind::Unblock { .. }) {
            continue;
        }
        match latest {
            None => latest = Some(a),
            Some(prev) if a.timestamp > prev.timestamp => latest = Some(a),
            Some(prev) if a.timestamp == prev.timestamp
                && matches!(a.kind, AttestationKind::Unblock { .. }) =>
            {
                latest = Some(a);
            }
            _ => {}
        }
    }
    matches!(latest.map(|a| &a.kind), Some(AttestationKind::Block { .. }))
}

/// Verification method for [`AttestationKind::Spec`]. Mirrors the
/// tag the spec checker already uses — kept as a string so the
/// vcs crate doesn't have to pull `spec-checker` in.
#[derive(Debug, Clone, Copy, PartialEq, Eq, Serialize, Deserialize)]
#[serde(rename_all = "snake_case")]
pub enum SpecMethod {
    /// Exhaustive search; `trials` is unset.
    Exhaustive,
    /// Random sampling; `trials` carries the sample count.
    Random,
    /// Symbolic execution.
    Symbolic,
}

/// Whether the verification succeeded. `Inconclusive` is its own
/// state because some checkers (e.g. random-sampling spec checks
/// over an unbounded input space) can pass within their budget
/// without proving the contract holds in general.
#[derive(Debug, Clone, PartialEq, Eq, Serialize, Deserialize)]
#[serde(tag = "result", rename_all = "snake_case")]
pub enum AttestationResult {
    Passed,
    Failed { detail: String },
    Inconclusive { detail: String },
}

/// Who produced this attestation. `tool` is the CLI / harness name
/// (`"lex check"`, `"lex agent-tool"`, `"ci-runner@v3"`). `version`
/// pins the tool revision so a regression in the producer is
/// distinguishable from a regression in the code being verified.
/// `model` is set when an LLM was the proximate producer — for
/// `--spec`-style runs the harness is the producer; for `lex
/// agent-tool` the model is, and we want both recorded.
#[derive(Debug, Clone, PartialEq, Eq, Serialize, Deserialize)]
pub struct ProducerDescriptor {
    pub tool: String,
    pub version: String,
    #[serde(default, skip_serializing_if = "Option::is_none")]
    pub model: Option<String>,
}

/// Optional cost record. Excluded from the attestation hash so
/// rerunning a verification on a different machine (different
/// wall-clock, different token pricing) doesn't break dedup.
#[derive(Debug, Clone, PartialEq, Eq, Serialize, Deserialize)]
pub struct Cost {
    #[serde(default, skip_serializing_if = "Option::is_none")]
    pub tokens_in: Option<u64>,
    #[serde(default, skip_serializing_if = "Option::is_none")]
    pub tokens_out: Option<u64>,
    /// USD cents (avoid floating-point in persisted form).
    #[serde(default, skip_serializing_if = "Option::is_none")]
    pub usd_cents: Option<u64>,
    #[serde(default, skip_serializing_if = "Option::is_none")]
    pub wall_time_ms: Option<u64>,
}

/// Optional Ed25519 signature over the attestation hash. Verifying
/// it is the consumer's job; the data layer just stores the bytes.
#[derive(Debug, Clone, PartialEq, Eq, Serialize, Deserialize)]
pub struct Signature {
    /// Hex-encoded Ed25519 public key.
    pub public_key: String,
    /// Hex-encoded signature over the lowercase-hex `attestation_id`.
    pub signature: String,
}

/// The persisted attestation. See module docs for what each field
/// is, what's in the hash, and what isn't.
#[derive(Debug, Clone, PartialEq, Eq, Serialize, Deserialize)]
pub struct Attestation {
    pub attestation_id: AttestationId,
    pub stage_id: StageId,
    #[serde(default, skip_serializing_if = "Option::is_none")]
    pub op_id: Option<OpId>,
    #[serde(default, skip_serializing_if = "Option::is_none")]
    pub intent_id: Option<IntentId>,
    pub kind: AttestationKind,
    pub result: AttestationResult,
    pub produced_by: ProducerDescriptor,
    #[serde(default, skip_serializing_if = "Option::is_none")]
    pub cost: Option<Cost>,
    /// Wall-clock seconds since epoch when this attestation was
    /// produced. Excluded from `attestation_id` so the dedup
    /// property holds across runs.
    pub timestamp: u64,
    #[serde(default, skip_serializing_if = "Option::is_none")]
    pub signature: Option<Signature>,
}

impl Attestation {
    /// Build an attestation against a stage, computing its
    /// content-addressed id. `timestamp` defaults to the current
    /// wall clock; pass to [`Attestation::with_timestamp`] in tests.
    #[allow(clippy::too_many_arguments)]
    pub fn new(
        stage_id: impl Into<StageId>,
        op_id: Option<OpId>,
        intent_id: Option<IntentId>,
        kind: AttestationKind,
        result: AttestationResult,
        produced_by: ProducerDescriptor,
        cost: Option<Cost>,
    ) -> Self {
        let now = SystemTime::now()
            .duration_since(UNIX_EPOCH)
            .map(|d| d.as_secs())
            .unwrap_or(0);
        Self::with_timestamp(stage_id, op_id, intent_id, kind, result, produced_by, cost, now)
    }

    /// Build an attestation with a caller-controlled `timestamp`.
    /// Used in tests to keep golden hashes stable.
    #[allow(clippy::too_many_arguments)]
    pub fn with_timestamp(
        stage_id: impl Into<StageId>,
        op_id: Option<OpId>,
        intent_id: Option<IntentId>,
        kind: AttestationKind,
        result: AttestationResult,
        produced_by: ProducerDescriptor,
        cost: Option<Cost>,
        timestamp: u64,
    ) -> Self {
        let stage_id = stage_id.into();
        let attestation_id = compute_attestation_id(
            &stage_id,
            op_id.as_deref(),
            intent_id.as_deref(),
            &kind,
            &result,
            &produced_by,
        );
        Self {
            attestation_id,
            stage_id,
            op_id,
            intent_id,
            kind,
            result,
            produced_by,
            cost,
            timestamp,
            signature: None,
        }
    }

    /// Attach a signature. The signature is not part of the hash;
    /// the same logical attestation produced by an unsigned harness
    /// dedupes against a signed one. Callers who *want* signature
    /// to be part of identity should hash signature into the
    /// `produced_by.tool` string explicitly.
    pub fn with_signature(mut self, signature: Signature) -> Self {
        self.signature = Some(signature);
        self
    }
}

fn compute_attestation_id(
    stage_id: &str,
    op_id: Option<&str>,
    intent_id: Option<&str>,
    kind: &AttestationKind,
    result: &AttestationResult,
    produced_by: &ProducerDescriptor,
) -> AttestationId {
    let view = CanonicalAttestationView {
        stage_id,
        op_id,
        intent_id,
        kind,
        result,
        produced_by,
    };
    canonical::hash(&view)
}

/// Hashable shadow of [`Attestation`] omitting the fields we
/// deliberately exclude from identity (`attestation_id`, `cost`,
/// `timestamp`, `signature`). Lives only as a transient.
#[derive(Serialize)]
struct CanonicalAttestationView<'a> {
    stage_id: &'a str,
    #[serde(skip_serializing_if = "Option::is_none")]
    op_id: Option<&'a str>,
    #[serde(skip_serializing_if = "Option::is_none")]
    intent_id: Option<&'a str>,
    kind: &'a AttestationKind,
    result: &'a AttestationResult,
    produced_by: &'a ProducerDescriptor,
}

// ---- Persistence -------------------------------------------------

/// Persistent log of [`Attestation`] records.
///
/// Mirrors [`crate::OpLog`] / [`crate::IntentLog`] in shape: one
/// canonical-JSON file per attestation, atomic writes via tempfile +
/// rename, idempotent on re-puts. Maintains two secondary indices
/// for cheap reverse lookups:
///
/// * `by-stage/<StageId>/<AttestationId>` — every attestation,
///   indexed by the stage it records evidence for.
/// * `by-run/<TraceRunId>/<AttestationId>` (#246) — only
///   `AttestationKind::Trace` entries are indexed here, so
///   `list_for_run` is `O(traces of that run)` rather than scanning
///   the whole log.
pub struct AttestationLog {
    dir: PathBuf,
    by_stage: PathBuf,
    by_run: PathBuf,
}

impl AttestationLog {
    pub fn open(root: &Path) -> io::Result<Self> {
        let dir = root.join("attestations");
        let by_stage = dir.join("by-stage");
        let by_run = dir.join("by-run");
        fs::create_dir_all(&by_stage)?;
        fs::create_dir_all(&by_run)?;
        Ok(Self { dir, by_stage, by_run })
    }

    fn primary_path(&self, id: &AttestationId) -> PathBuf {
        self.dir.join(format!("{id}.json"))
    }

    /// Persist an attestation. Idempotent on existing ids — content
    /// addressing guarantees the same logical attestation produces
    /// the same id, so re-putting is a no-op for the primary file.
    /// The by-stage index is also re-written idempotently.
    pub fn put(&self, attestation: &Attestation) -> io::Result<()> {
        let primary = self.primary_path(&attestation.attestation_id);
        if !primary.exists() {
            let bytes = serde_json::to_vec(attestation)
                .map_err(|e| io::Error::new(io::ErrorKind::InvalidData, e))?;
            let tmp = primary.with_extension("json.tmp");
            let mut f = fs::File::create(&tmp)?;
            f.write_all(&bytes)?;
            f.sync_all()?;
            fs::rename(&tmp, &primary)?;
        }
        // Index entry: empty marker file. Reading the index is a
        // directory listing; resolving each entry is a primary-file
        // read by id.
        let stage_dir = self.by_stage.join(&attestation.stage_id);
        fs::create_dir_all(&stage_dir)?;
        let idx = stage_dir.join(&attestation.attestation_id);
        if !idx.exists() {
            fs::File::create(&idx)?;
        }
        // by-run secondary index for Trace attestations (#246) —
        // only the variants that carry a `run_id` are indexed; every
        // other kind skips this directory entirely.
        if let AttestationKind::Trace { run_id, .. } = &attestation.kind {
            let run_dir = self.by_run.join(run_id);
            fs::create_dir_all(&run_dir)?;
            let idx = run_dir.join(&attestation.attestation_id);
            if !idx.exists() {
                fs::File::create(&idx)?;
            }
        }
        Ok(())
    }

    /// Remove an attestation from the log along with both index
    /// entries (#258). Idempotent on missing files.
    ///
    /// **Not** part of the day-to-day API — the attestation log is
    /// append-only by design (#132). The only legitimate caller is
    /// the migration tool, which supervises a destructive,
    /// `--confirm`-gated batch.
    pub fn delete(&self, attestation: &Attestation) -> io::Result<()> {
        let primary = self.primary_path(&attestation.attestation_id);
        match fs::remove_file(&primary) {
            Ok(()) | Err(_) => {} // best-effort; missing is fine
        }
        let stage_idx = self.by_stage
            .join(&attestation.stage_id)
            .join(&attestation.attestation_id);
        let _ = fs::remove_file(&stage_idx);
        if let AttestationKind::Trace { run_id, .. } = &attestation.kind {
            let run_idx = self.by_run.join(run_id).join(&attestation.attestation_id);
            let _ = fs::remove_file(&run_idx);
        }
        Ok(())
    }

    pub fn get(&self, id: &AttestationId) -> io::Result<Option<Attestation>> {
        let path = self.primary_path(id);
        if !path.exists() {
            return Ok(None);
        }
        let bytes = fs::read(&path)?;
        let attestation: Attestation = serde_json::from_slice(&bytes)
            .map_err(|e| io::Error::new(io::ErrorKind::InvalidData, e))?;
        Ok(Some(attestation))
    }

    /// Enumerate every attestation in the log. Walks
    /// `<root>/attestations/*.json` directly — no per-stage index
    /// — so cost is `O(total attestations)`. Used by `lex attest
    /// filter` for CI / dashboard queries that span stages.
    /// Order is not stable; callers that need stable ordering
    /// should sort by `timestamp` or `attestation_id`.
    pub fn list_all(&self) -> io::Result<Vec<Attestation>> {
        let mut out = Vec::new();
        if !self.dir.exists() {
            return Ok(out);
        }
        for entry in fs::read_dir(&self.dir)? {
            let entry = entry?;
            let p = entry.path();
            // Skip the by-stage/ subdir and the .tmp staging files
            // a crashed put might have left behind.
            if p.is_dir() {
                continue;
            }
            if p.extension().is_none_or(|e| e != "json") {
                continue;
            }
            let bytes = fs::read(&p)?;
            // A corrupt primary file shouldn't take down a filter
            // query — log to stderr and skip.
            match serde_json::from_slice::<Attestation>(&bytes) {
                Ok(att) => out.push(att),
                Err(e) => eprintln!(
                    "warning: skipping unreadable attestation {}: {e}",
                    p.display()
                ),
            }
        }
        Ok(out)
    }

    /// Enumerate attestations for a given stage. Order is not
    /// stable across calls (it follows directory iteration order).
    /// Callers that need a stable ordering should sort by
    /// `timestamp` or `attestation_id`.
    pub fn list_for_stage(&self, stage_id: &StageId) -> io::Result<Vec<Attestation>> {
        let stage_dir = self.by_stage.join(stage_id);
        if !stage_dir.exists() {
            return Ok(Vec::new());
        }
        let mut out = Vec::new();
        for entry in fs::read_dir(&stage_dir)? {
            let entry = entry?;
            let id = match entry.file_name().into_string() {
                Ok(s) => s,
                Err(_) => continue,
            };
            if let Some(att) = self.get(&id)? {
                out.push(att);
            }
        }
        Ok(out)
    }

    /// Enumerate `AttestationKind::Trace` entries for a given
    /// `run_id` (#246). Walks the `by-run/<run_id>/` directory; cost
    /// is `O(trace attestations for that run)`, typically 1.
    /// Returns an empty vec if the run has no Trace attestations.
    /// Order is not stable.
    pub fn list_for_run(&self, run_id: &TraceRunId) -> io::Result<Vec<Attestation>> {
        let run_dir = self.by_run.join(run_id);
        if !run_dir.exists() {
            return Ok(Vec::new());
        }
        let mut out = Vec::new();
        for entry in fs::read_dir(&run_dir)? {
            let entry = entry?;
            let id = match entry.file_name().into_string() {
                Ok(s) => s,
                Err(_) => continue,
            };
            if let Some(att) = self.get(&id)? {
                out.push(att);
            }
        }
        Ok(out)
    }
}

// ---- Tests --------------------------------------------------------

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

    fn ci_runner() -> ProducerDescriptor {
        ProducerDescriptor {
            tool: "lex check".into(),
            version: "0.1.0".into(),
            model: None,
        }
    }

    fn typecheck_passed() -> Attestation {
        Attestation::with_timestamp(
            "stage-abc",
            Some("op-123".into()),
            None,
            AttestationKind::TypeCheck,
            AttestationResult::Passed,
            ci_runner(),
            None,
            1000,
        )
    }

    #[test]
    fn same_logical_verification_hashes_equal() {
        // Dedup invariant: same stage, same kind, same producer,
        // same outcome → same `attestation_id` regardless of
        // wall-clock or cost.
        let a = typecheck_passed();
        let b = Attestation::with_timestamp(
            "stage-abc",
            Some("op-123".into()),
            None,
            AttestationKind::TypeCheck,
            AttestationResult::Passed,
            ci_runner(),
            Some(Cost {
                tokens_in: Some(0),
                tokens_out: Some(0),
                usd_cents: Some(0),
                wall_time_ms: Some(42),
            }),
            99999,
        );
        assert_eq!(a.attestation_id, b.attestation_id);
    }

    #[test]
    fn different_stages_hash_differently() {
        let a = typecheck_passed();
        let b = Attestation::with_timestamp(
            "stage-XYZ",
            Some("op-123".into()),
            None,
            AttestationKind::TypeCheck,
            AttestationResult::Passed,
            ci_runner(),
            None,
            1000,
        );
        assert_ne!(a.attestation_id, b.attestation_id);
    }

    #[test]
    fn different_op_ids_hash_differently() {
        let a = typecheck_passed();
        let b = Attestation::with_timestamp(
            "stage-abc",
            Some("op-XYZ".into()),
            None,
            AttestationKind::TypeCheck,
            AttestationResult::Passed,
            ci_runner(),
            None,
            1000,
        );
        assert_ne!(a.attestation_id, b.attestation_id);
    }

    #[test]
    fn different_intents_hash_differently() {
        let a = Attestation::with_timestamp(
            "stage-abc", None,
            Some("intent-A".into()),
            AttestationKind::TypeCheck, AttestationResult::Passed,
            ci_runner(), None, 1000,
        );
        let b = Attestation::with_timestamp(
            "stage-abc", None,
            Some("intent-B".into()),
            AttestationKind::TypeCheck, AttestationResult::Passed,
            ci_runner(), None, 1000,
        );
        assert_ne!(a.attestation_id, b.attestation_id);
    }

    #[test]
    fn different_kinds_hash_differently() {
        let a = typecheck_passed();
        let b = Attestation::with_timestamp(
            "stage-abc",
            Some("op-123".into()),
            None,
            AttestationKind::EffectAudit,
            AttestationResult::Passed,
            ci_runner(),
            None,
            1000,
        );
        assert_ne!(a.attestation_id, b.attestation_id);
    }

    #[test]
    fn passed_vs_failed_hash_differently() {
        // Critical: a Failed attestation must not collide with a
        // Passed one for the same logical verification. Otherwise
        // a flaky producer could overwrite the negative evidence
        // by re-running and getting Passed.
        let a = typecheck_passed();
        let b = Attestation::with_timestamp(
            "stage-abc",
            Some("op-123".into()),
            None,
            AttestationKind::TypeCheck,
            AttestationResult::Failed { detail: "arity mismatch".into() },
            ci_runner(),
            None,
            1000,
        );
        assert_ne!(a.attestation_id, b.attestation_id);
    }

    #[test]
    fn different_producers_hash_differently() {
        let a = typecheck_passed();
        let mut other = ci_runner();
        other.tool = "third-party-runner".into();
        let b = Attestation::with_timestamp(
            "stage-abc",
            Some("op-123".into()),
            None,
            AttestationKind::TypeCheck,
            AttestationResult::Passed,
            other,
            None,
            1000,
        );
        assert_ne!(
            a.attestation_id, b.attestation_id,
            "an attestation from a different producer is a different fact",
        );
    }

    #[test]
    fn signature_is_excluded_from_hash() {
        // A signed and unsigned attestation of the same logical
        // fact must dedupe. Otherwise late-signing a record would
        // create two attestations that say the same thing.
        let a = typecheck_passed();
        let b = typecheck_passed().with_signature(Signature {
            public_key: "ed25519:fffe".into(),
            signature: "0xabcd".into(),
        });
        assert_eq!(a.attestation_id, b.attestation_id);
    }

    #[test]
    fn attestation_id_is_64_char_lowercase_hex() {
        let a = typecheck_passed();
        assert_eq!(a.attestation_id.len(), 64);
        assert!(a
            .attestation_id
            .chars()
            .all(|c| c.is_ascii_digit() || ('a'..='f').contains(&c)));
    }

    #[test]
    fn round_trip_through_serde_json() {
        let a = Attestation::with_timestamp(
            "stage-abc",
            Some("op-123".into()),
            Some("intent-A".into()),
            AttestationKind::Spec {
                spec_id: "clamp.spec".into(),
                method: SpecMethod::Random,
                trials: Some(1000),
            },
            AttestationResult::Passed,
            ProducerDescriptor {
                tool: "lex agent-tool".into(),
                version: "0.1.0".into(),
                model: Some("claude-opus-4-7".into()),
            },
            Some(Cost {
                tokens_in: Some(1234),
                tokens_out: Some(567),
                usd_cents: Some(2),
                wall_time_ms: Some(3400),
            }),
            99,
        )
        .with_signature(Signature {
            public_key: "ed25519:abc".into(),
            signature: "0x1234".into(),
        });
        let json = serde_json::to_string(&a).unwrap();
        let back: Attestation = serde_json::from_str(&json).unwrap();
        assert_eq!(a, back);
    }

    /// Golden hash. If this changes, the canonical form has shifted
    /// — every `AttestationId` in every existing store has changed
    /// too. Update with care; same protective shape as the
    /// `Operation` and `Intent` golden tests.
    #[test]
    fn canonical_form_is_stable_for_a_known_input() {
        let a = Attestation::with_timestamp(
            "stage-abc",
            Some("op-123".into()),
            None,
            AttestationKind::TypeCheck,
            AttestationResult::Passed,
            ProducerDescriptor {
                tool: "lex check".into(),
                version: "0.1.0".into(),
                model: None,
            },
            None,
            0,
        );
        assert_eq!(
            a.attestation_id,
            "a4ef921f7bb0db70779c5b698cda1744d49165a4a56aa8414bdbafc85bcbc16b",
            "canonical-form regression: the AttestationId for a known input changed",
        );
    }

    // ---- AttestationLog ----

    #[test]
    fn log_round_trips_through_disk() {
        let tmp = tempfile::tempdir().unwrap();
        let log = AttestationLog::open(tmp.path()).unwrap();
        let a = typecheck_passed();
        log.put(&a).unwrap();
        let read_back = log.get(&a.attestation_id).unwrap().unwrap();
        assert_eq!(a, read_back);
    }

    #[test]
    fn log_get_unknown_returns_none() {
        let tmp = tempfile::tempdir().unwrap();
        let log = AttestationLog::open(tmp.path()).unwrap();
        assert!(log
            .get(&"nonexistent".to_string())
            .unwrap()
            .is_none());
    }

    #[test]
    fn log_put_is_idempotent() {
        let tmp = tempfile::tempdir().unwrap();
        let log = AttestationLog::open(tmp.path()).unwrap();
        let a = typecheck_passed();
        log.put(&a).unwrap();
        log.put(&a).unwrap();
        let read_back = log.get(&a.attestation_id).unwrap().unwrap();
        assert_eq!(a, read_back);
    }

    #[test]
    fn list_for_stage_returns_only_that_stage() {
        let tmp = tempfile::tempdir().unwrap();
        let log = AttestationLog::open(tmp.path()).unwrap();

        let on_abc_1 = typecheck_passed();
        let on_abc_2 = Attestation::with_timestamp(
            "stage-abc",
            Some("op-123".into()),
            None,
            AttestationKind::EffectAudit,
            AttestationResult::Passed,
            ci_runner(),
            None,
            2000,
        );
        let on_xyz = Attestation::with_timestamp(
            "stage-xyz",
            Some("op-456".into()),
            None,
            AttestationKind::TypeCheck,
            AttestationResult::Passed,
            ci_runner(),
            None,
            1000,
        );

        log.put(&on_abc_1).unwrap();
        log.put(&on_abc_2).unwrap();
        log.put(&on_xyz).unwrap();

        let mut on_abc = log.list_for_stage(&"stage-abc".to_string()).unwrap();
        on_abc.sort_by_key(|a| a.timestamp);
        assert_eq!(on_abc.len(), 2);
        assert_eq!(on_abc[0], on_abc_1);
        assert_eq!(on_abc[1], on_abc_2);

        let on_xyz_listed = log.list_for_stage(&"stage-xyz".to_string()).unwrap();
        assert_eq!(on_xyz_listed.len(), 1);
        assert_eq!(on_xyz_listed[0], on_xyz);
    }

    #[test]
    fn list_for_unknown_stage_is_empty() {
        let tmp = tempfile::tempdir().unwrap();
        let log = AttestationLog::open(tmp.path()).unwrap();
        let v = log.list_for_stage(&"never-attested".to_string()).unwrap();
        assert!(v.is_empty());
    }

    #[test]
    fn list_all_returns_every_persisted_attestation() {
        // Cross-stage enumeration: `list_all` walks the primary
        // directory regardless of stage, so a CI / dashboard query
        // can filter across the whole log without iterating the
        // by-stage index.
        let tmp = tempfile::tempdir().unwrap();
        let log = AttestationLog::open(tmp.path()).unwrap();
        let on_abc = typecheck_passed();
        let on_xyz = Attestation::with_timestamp(
            "stage-xyz",
            Some("op-456".into()),
            None,
            AttestationKind::TypeCheck,
            AttestationResult::Passed,
            ci_runner(),
            None,
            2000,
        );
        log.put(&on_abc).unwrap();
        log.put(&on_xyz).unwrap();
        let mut all = log.list_all().unwrap();
        all.sort_by_key(|a| a.attestation_id.clone());
        assert_eq!(all.len(), 2);
        let ids: BTreeSet<_> = all.iter().map(|a| a.attestation_id.clone()).collect();
        assert!(ids.contains(&on_abc.attestation_id));
        assert!(ids.contains(&on_xyz.attestation_id));
    }

    #[test]
    fn list_all_on_empty_log_is_empty() {
        let tmp = tempfile::tempdir().unwrap();
        let log = AttestationLog::open(tmp.path()).unwrap();
        let v = log.list_all().unwrap();
        assert!(v.is_empty());
    }

    #[test]
    fn passed_and_failed_for_same_stage_both_persist() {
        // Failure attestations are evidence too; they must not be
        // overwritten by a later passing attestation. The hash
        // distinction (tested above) plus the by-stage listing
        // should keep both visible.
        let tmp = tempfile::tempdir().unwrap();
        let log = AttestationLog::open(tmp.path()).unwrap();

        let passed = typecheck_passed();
        let failed = Attestation::with_timestamp(
            "stage-abc",
            Some("op-123".into()),
            None,
            AttestationKind::TypeCheck,
            AttestationResult::Failed { detail: "arity mismatch".into() },
            ci_runner(),
            None,
            500,
        );

        log.put(&failed).unwrap();
        log.put(&passed).unwrap();

        let listing = log.list_for_stage(&"stage-abc".to_string()).unwrap();
        assert_eq!(listing.len(), 2, "both passing and failing evidence must persist");
    }

    fn human_decision(kind: AttestationKind, ts: u64) -> Attestation {
        Attestation::with_timestamp(
            "stage-abc",
            None, None,
            kind,
            AttestationResult::Passed,
            ProducerDescriptor {
                tool: "lex stage".into(),
                version: "0.1.0".into(),
                model: None,
            },
            None,
            ts,
        )
    }

    #[test]
    fn is_stage_blocked_empty_log_is_false() {
        assert!(!is_stage_blocked(&[]));
    }

    #[test]
    fn is_stage_blocked_only_unrelated_attestations() {
        // TypeCheck/Override attestations don't gate activation —
        // only Block/Unblock do.
        let attestations = vec![
            typecheck_passed(),
            human_decision(
                AttestationKind::Override {
                    actor: "alice".into(),
                    reason: "ship".into(),
                    target_attestation_id: None,
                },
                500,
            ),
        ];
        assert!(!is_stage_blocked(&attestations));
    }

    #[test]
    fn is_stage_blocked_block_alone_blocks() {
        let attestations = vec![human_decision(
            AttestationKind::Block { actor: "alice".into(), reason: "x".into() },
            500,
        )];
        assert!(is_stage_blocked(&attestations));
    }

    #[test]
    fn is_stage_blocked_later_unblock_clears_block() {
        let attestations = vec![
            human_decision(
                AttestationKind::Block { actor: "alice".into(), reason: "x".into() },
                500,
            ),
            human_decision(
                AttestationKind::Unblock { actor: "alice".into(), reason: "ok".into() },
                600,
            ),
        ];
        assert!(!is_stage_blocked(&attestations));
    }

    #[test]
    fn is_stage_blocked_later_block_re_blocks() {
        let attestations = vec![
            human_decision(
                AttestationKind::Block { actor: "a".into(), reason: "1".into() },
                500,
            ),
            human_decision(
                AttestationKind::Unblock { actor: "a".into(), reason: "2".into() },
                600,
            ),
            human_decision(
                AttestationKind::Block { actor: "a".into(), reason: "3".into() },
                700,
            ),
        ];
        assert!(is_stage_blocked(&attestations));
    }

    #[test]
    fn is_stage_blocked_unblock_wins_at_same_timestamp() {
        // Tie-break favours Unblock so a hasty re-attempt at the
        // same wall-clock second can't strand the stage.
        let attestations = vec![
            human_decision(
                AttestationKind::Block { actor: "a".into(), reason: "1".into() },
                500,
            ),
            human_decision(
                AttestationKind::Unblock { actor: "a".into(), reason: "2".into() },
                500,
            ),
        ];
        assert!(!is_stage_blocked(&attestations));
    }
}