crtx-ledger 0.1.0

//! External anchor receipt primitive (ADR 0013 Mechanism C foundation).
//!
//! This module defines the **parser-only** v1 surface for the external
//! anchor authority work: the typed [`ExternalSink`] selector, the
//! [`ExternalReceipt`] struct, the canonical header
//! [`EXTERNAL_RECEIPT_FORMAT_HEADER_V1`], and a fail-closed parser for
//! single records and append-only receipt histories.
//!
//! **Out of scope (intentional):** live submission to Rekor or
//! OpenTimestamps, Rekor `SignedEntryTimestamp` cryptographic verification,
//! and OTS `.ots` binary-proof verification. Those wait on operator
//! decisions enumerated in `docs/design/DESIGN_external_anchor_authority.md`
//! §Residual risk — specifically the Rekor public key pin, the
//! ECDSA-P-256 vs Ed25519 choice for `SignedEntryTimestamp`, and the OTS
//! binary proof format. The parser here is sufficient to round-trip
//! receipts that an operator obtained out-of-band and to refuse anything
//! that is not a fully-specified v1 sidecar.
//!
//! The text format mirrors the existing position-bound `LedgerAnchor`
//! format: a one-line `# cortex-external-anchor-receipt-format: 1` header
//! followed by exactly one JSON body line. Receipt histories are the same
//! record repeated back-to-back, with monotonicity on `anchor_event_count`
//! enforced by [`parse_external_receipt_history`].
//!
//! ```text
//! # cortex-external-anchor-receipt-format: 1
//! {"sink":"rekor", "anchor_text_sha256":"<hex>", ...}
//! # cortex-external-anchor-receipt-format: 1
//! {"sink":"opentimestamps", "anchor_text_sha256":"<hex>", ...}
//! ```

pub mod ots;
pub mod rekor;
pub mod trusted_root;

use std::fmt;
use std::path::{Path, PathBuf};
use std::time::Duration;

use chrono::{DateTime, Utc};
use serde::{Deserialize, Serialize};
use thiserror::Error;

use crate::anchor::{verify_anchor, AnchorParseError, AnchorVerifyError, LedgerAnchor};
use crate::sha256::sha256_hex;

pub use trusted_root::{
    active_trusted_root, ActiveTrustedRoot, TransparencyLogInstance, TransparencyLogPublicKey,
    TrustRootStalenessAnchor, TrustRootStalenessError, TrustedRoot, TrustedRootIoError,
    TrustedRootKeyError, TrustedRootParseError, ValidityPeriod, CACHED_ROOT_STATUS,
    DEFAULT_MAX_TRUST_ROOT_AGE, EMBEDDED_ROOT_STATUS, EMBEDDED_TRUSTED_ROOT_SNAPSHOT_DATE,
    REKOR_TRUSTED_ROOT_TLOG_LOGID_NO_MATCH_INVARIANT, TRUSTED_ROOT_CACHE_STALE_INVARIANT,
    TRUSTED_ROOT_JSON, TRUSTED_ROOT_PARSE_INVARIANT, TRUSTED_ROOT_SNAPSHOT_STALE_INVARIANT,
    TRUSTED_ROOT_STALE_INVARIANT,
};

/// Header required at the top of every v1 external anchor receipt record.
pub const EXTERNAL_RECEIPT_FORMAT_HEADER_V1: &str = "# cortex-external-anchor-receipt-format: 1";

/// SHA-256 hex digest length, in lowercase ASCII characters.
const SHA256_HEX_LEN: usize = 64;

/// BLAKE3 hex digest length used elsewhere in the ledger; reused for
/// `anchor_chain_head_hash` validation since the receipt mirrors a
/// [`crate::LedgerAnchor`] chain head.
const BLAKE3_HEX_LEN: usize = 64;

/// Typed external anchor sink selector.
///
/// `None` is the doctrine default: no external sink is configured and no
/// receipt can be emitted. The two adapter-bound variants are currently
/// parser-only — submitting and verifying with a live network adapter is
/// deferred per the design doc.
#[derive(Debug, Clone, Copy, PartialEq, Eq, Hash)]
pub enum ExternalSink {
    /// No external sink configured. Fail-closed default.
    None,
    /// Sigstore Rekor public transparency log.
    Rekor,
    /// OpenTimestamps Bitcoin-rooted calendar proof.
    OpenTimestamps,
}

impl ExternalSink {
    /// Stable wire token for the `sink` field of an [`ExternalReceipt`].
    #[must_use]
    pub const fn as_wire_str(self) -> &'static str {
        match self {
            Self::None => "none",
            Self::Rekor => "rekor",
            Self::OpenTimestamps => "opentimestamps",
        }
    }

    /// Parse a wire-form sink token. Unknown tokens fail closed.
    pub fn from_wire_str(value: &str) -> Result<Self, ExternalReceiptParseError> {
        match value {
            "none" => Ok(Self::None),
            "rekor" => Ok(Self::Rekor),
            "opentimestamps" => Ok(Self::OpenTimestamps),
            other => Err(ExternalReceiptParseError::UnknownSink {
                observed: other.to_string(),
            }),
        }
    }
}

impl fmt::Display for ExternalSink {
    fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
        f.write_str(self.as_wire_str())
    }
}

/// v1 external anchor receipt sidecar.
///
/// Mirrors the JSON shape in `DESIGN_external_anchor_authority.md` §Receipt
/// shape. `receipt` carries the sink-specific payload and is intentionally
/// left as `serde_json::Value`: Rekor and OpenTimestamps each pin their own
/// shape inside this field, but the live adapters that consume them are
/// deferred. Unknown fields inside `receipt` are not validated here.
#[derive(Debug, Clone, PartialEq, Eq, Serialize, Deserialize)]
pub struct ExternalReceipt {
    /// Sink that produced this receipt.
    pub sink: ExternalSink,
    /// Lowercase hex SHA-256 over the canonical [`crate::LedgerAnchor`] text
    /// at the witnessed position. The verifier recomputes this against the
    /// local ledger; mismatch is `external_anchor_receipts.anchor_text_hash.mismatch`.
    pub anchor_text_sha256: String,
    /// Event count at the witnessed position.
    pub anchor_event_count: u64,
    /// Lowercase hex BLAKE3 ledger event hash at `anchor_event_count`.
    pub anchor_chain_head_hash: String,
    /// RFC 3339 submission timestamp recorded by the operator client.
    pub submitted_at: DateTime<Utc>,
    /// Sink endpoint actually contacted (e.g. `https://rekor.sigstore.dev`).
    pub sink_endpoint: String,
    /// Sink-specific payload (Rekor entry envelope or OTS proof envelope).
    pub receipt: serde_json::Value,
}

impl ExternalReceipt {
    /// Render this receipt as a canonical v1 record: header line, then the
    /// JSON body on one line, then a trailing newline.
    pub fn to_record_text(&self) -> Result<String, ExternalReceiptParseError> {
        let body = serde_json::to_string(self).map_err(|source| {
            ExternalReceiptParseError::MalformedBody {
                reason: format!("failed to serialize receipt body: {source}"),
            }
        })?;
        Ok(format!("{EXTERNAL_RECEIPT_FORMAT_HEADER_V1}\n{body}\n"))
    }
}

impl ExternalSink {
    /// Custom serde representation: emit `as_wire_str`, parse via
    /// `from_wire_str`. This keeps the wire token stable even if the enum
    /// reorders.
    fn serialize_sink<S>(sink: &Self, ser: S) -> Result<S::Ok, S::Error>
    where
        S: serde::Serializer,
    {
        ser.serialize_str(sink.as_wire_str())
    }

    fn deserialize_sink<'de, D>(de: D) -> Result<Self, D::Error>
    where
        D: serde::Deserializer<'de>,
    {
        let raw = String::deserialize(de)?;
        Self::from_wire_str(&raw).map_err(serde::de::Error::custom)
    }
}

// The ExternalSink serde adapter has to flow through ExternalReceipt's serde
// derive without losing the wire-token contract. We achieve that by wiring
// the field via #[serde(serialize_with / deserialize_with)] below.
impl Serialize for ExternalSink {
    fn serialize<S>(&self, ser: S) -> Result<S::Ok, S::Error>
    where
        S: serde::Serializer,
    {
        Self::serialize_sink(self, ser)
    }
}

impl<'de> Deserialize<'de> for ExternalSink {
    fn deserialize<D>(de: D) -> Result<Self, D::Error>
    where
        D: serde::Deserializer<'de>,
    {
        Self::deserialize_sink(de)
    }
}

/// Parse a single v1 external anchor receipt record from text.
///
/// Expects exactly two structural lines: the [`EXTERNAL_RECEIPT_FORMAT_HEADER_V1`]
/// header and a one-line JSON body. Trailing content, missing header, or
/// missing body all fail closed.
pub fn parse_external_receipt(input: &str) -> Result<ExternalReceipt, ExternalReceiptParseError> {
    let mut lines = input.lines();
    let Some(header) = lines.next() else {
        return Err(ExternalReceiptParseError::MissingHeader);
    };
    if header != EXTERNAL_RECEIPT_FORMAT_HEADER_V1 {
        return Err(ExternalReceiptParseError::UnknownFormatHeader {
            observed: header.to_string(),
        });
    }

    let Some(body) = lines.next() else {
        return Err(ExternalReceiptParseError::MissingBody);
    };
    if body.trim() != body {
        return Err(ExternalReceiptParseError::MalformedBody {
            reason: "body line must not have leading or trailing whitespace".to_string(),
        });
    }
    if body.is_empty() {
        return Err(ExternalReceiptParseError::MalformedBody {
            reason: "body line must not be empty".to_string(),
        });
    }
    if lines.next().is_some() {
        return Err(ExternalReceiptParseError::TrailingContent);
    }

    let receipt: ExternalReceipt =
        serde_json::from_str(body).map_err(|source| ExternalReceiptParseError::MalformedBody {
            reason: format!("invalid receipt JSON: {source}"),
        })?;
    validate_external_receipt_fields(&receipt)?;
    Ok(receipt)
}

/// Parse a v1 external anchor receipt history from repeated canonical records.
///
/// Mirrors [`crate::anchor::parse_anchor_history`]: receipts are the
/// `header\nbody\n` record repeated back-to-back. Monotonicity on
/// `anchor_event_count` is enforced — a later record may equal but must not
/// be less than the previous record's count. An empty history is a parse
/// error.
pub fn parse_external_receipt_history(
    input: &str,
) -> Result<Vec<ExternalReceipt>, ExternalReceiptParseError> {
    let mut lines = input.lines();
    let mut receipts = Vec::new();

    loop {
        let Some(header) = lines.next() else {
            break;
        };
        let Some(body) = lines.next() else {
            return Err(ExternalReceiptParseError::MissingBody);
        };
        receipts.push(parse_external_receipt(&format!("{header}\n{body}\n"))?);
    }

    if receipts.is_empty() {
        return Err(ExternalReceiptParseError::MissingHeader);
    }

    let mut previous_event_count: Option<u64> = None;
    for (index, receipt) in receipts.iter().enumerate() {
        if let Some(previous) = previous_event_count {
            if receipt.anchor_event_count < previous {
                return Err(ExternalReceiptParseError::NonMonotonic {
                    receipt_index: index + 1,
                    previous_event_count: previous,
                    event_count: receipt.anchor_event_count,
                });
            }
        }
        previous_event_count = Some(receipt.anchor_event_count);
    }

    Ok(receipts)
}

fn validate_external_receipt_fields(
    receipt: &ExternalReceipt,
) -> Result<(), ExternalReceiptParseError> {
    if receipt.sink == ExternalSink::None {
        return Err(ExternalReceiptParseError::UnknownSink {
            observed: ExternalSink::None.as_wire_str().to_string(),
        });
    }
    validate_lower_hex(
        &receipt.anchor_text_sha256,
        SHA256_HEX_LEN,
        "anchor_text_sha256",
    )?;
    validate_lower_hex(
        &receipt.anchor_chain_head_hash,
        BLAKE3_HEX_LEN,
        "anchor_chain_head_hash",
    )?;
    if receipt.sink_endpoint.is_empty() {
        return Err(ExternalReceiptParseError::MalformedBody {
            reason: "sink_endpoint must not be empty".to_string(),
        });
    }
    if receipt.anchor_event_count == 0 {
        return Err(ExternalReceiptParseError::MalformedBody {
            reason: "anchor_event_count must be positive".to_string(),
        });
    }
    if !receipt.receipt.is_object() {
        return Err(ExternalReceiptParseError::MalformedBody {
            reason: "receipt body field must be a JSON object".to_string(),
        });
    }
    Ok(())
}

fn validate_lower_hex(
    value: &str,
    expected_len: usize,
    field: &'static str,
) -> Result<(), ExternalReceiptParseError> {
    if value.len() != expected_len
        || !value
            .bytes()
            .all(|b| b.is_ascii_digit() || (b'a'..=b'f').contains(&b))
    {
        return Err(ExternalReceiptParseError::InvalidHexField {
            field,
            value: value.to_string(),
            expected_len,
        });
    }
    Ok(())
}

/// Parse errors for the v1 external anchor receipt text format.
#[derive(Debug, Clone, PartialEq, Eq, Error)]
pub enum ExternalReceiptParseError {
    /// No first line was present.
    #[error("missing external anchor receipt format header")]
    MissingHeader,
    /// Header was present but was not the supported v1 header.
    #[error("unknown external anchor receipt format header: {observed}")]
    UnknownFormatHeader {
        /// Header line found in the input.
        observed: String,
    },
    /// Header was present but the body line was absent.
    #[error("missing external anchor receipt body")]
    MissingBody,
    /// Body did not parse as a valid v1 receipt JSON document.
    #[error("malformed external anchor receipt body: {reason}")]
    MalformedBody {
        /// Human-readable parse failure.
        reason: String,
    },
    /// Extra non-format structure followed the body line.
    #[error("external anchor receipt has trailing content")]
    TrailingContent,
    /// Receipt referenced an unknown sink token.
    #[error("unknown external anchor receipt sink: {observed}")]
    UnknownSink {
        /// Sink token as parsed from the input.
        observed: String,
    },
    /// A hex field did not have the expected length or lowercase ASCII shape.
    #[error("invalid external anchor receipt {field}: expected {expected_len} lowercase hex chars, got `{value}`")]
    InvalidHexField {
        /// Field name in the receipt envelope.
        field: &'static str,
        /// Field value as parsed from the input.
        value: String,
        /// Expected number of hex characters.
        expected_len: usize,
    },
    /// Receipt history moved backwards in logical event position.
    #[error(
        "external anchor receipt history is non-monotonic at record {receipt_index}: event_count {event_count} follows {previous_event_count}"
    )]
    NonMonotonic {
        /// 1-based receipt record index.
        receipt_index: usize,
        /// Previous receipt event count.
        previous_event_count: u64,
        /// Current receipt event count.
        event_count: u64,
    },
}

/// I/O errors when reading a receipt history file off disk.
#[derive(Debug, Error)]
pub enum ExternalReceiptHistoryIoError {
    /// The history file could not be opened or read.
    #[error("failed to read external anchor receipt history {path:?}: {source}")]
    ReadHistory {
        /// Receipt history path that was being read.
        path: PathBuf,
        /// I/O failure.
        source: std::io::Error,
    },
    /// The receipt history text did not parse as repeated v1 receipt records.
    #[error("invalid external anchor receipt history {path:?}: {source}")]
    Parse {
        /// Receipt history path that was being parsed.
        path: PathBuf,
        /// Parse failure.
        source: ExternalReceiptParseError,
    },
}

/// Read a receipt history file and return the parsed monotonic record list.
pub fn read_external_receipt_history(
    path: impl Into<PathBuf>,
) -> Result<Vec<ExternalReceipt>, ExternalReceiptHistoryIoError> {
    let path = path.into();
    let text = std::fs::read_to_string(&path).map_err(|source| {
        ExternalReceiptHistoryIoError::ReadHistory {
            path: path.clone(),
            source,
        }
    })?;
    parse_external_receipt_history(&text)
        .map_err(|source| ExternalReceiptHistoryIoError::Parse { path, source })
}

/// Stable invariant identifier emitted when the recomputed
/// `anchor_text_sha256` for an external receipt does not match the local
/// ledger. Surfaced both in CLI diagnostics and in any future export
/// artifact so wrappers can grep for the exact token.
pub const ANCHOR_TEXT_HASH_MISMATCH_INVARIANT: &str =
    "external_anchor_receipts.anchor_text_hash.mismatch";

/// Stable status emitted by [`verify_external_receipts`] today: the parser
/// has confirmed the receipt envelope is well-formed and the local
/// position-bound anchor it claims matches the ledger, but the live Rekor
/// signature / OTS proof verification adapters are deferred. Operators and
/// dashboards key off this token to distinguish "parsed only" from a
/// future "fully cryptographically verified" status.
pub const PARSED_ONLY_VERIFICATION_STATUS: &str = "parsed_only_signature_verification_pending";

/// Successful external-receipt verification summary.
#[derive(Debug, Clone, PartialEq, Eq)]
pub struct ExternalReceiptVerification {
    /// Ledger path that was verified against.
    pub path: PathBuf,
    /// Receipt history path that was verified.
    pub receipts_path: PathBuf,
    /// Number of rows observed in the current ledger after scanning the
    /// last receipt position.
    pub db_count: u64,
    /// Number of receipts parsed and parser-verified.
    pub receipts_verified: usize,
    /// The latest receipt that was verified — has the largest
    /// `anchor_event_count`.
    pub latest_receipt: ExternalReceipt,
    /// Stable status string. See [`PARSED_ONLY_VERIFICATION_STATUS`].
    pub status: &'static str,
    /// Provenance token for the trusted root that was in force during
    /// verification. Either [`EMBEDDED_ROOT_STATUS`] when no operator
    /// cache was supplied or could be loaded, or [`CACHED_ROOT_STATUS`]
    /// when a refreshed cache was active.
    pub trust_root_status: &'static str,
    /// Activation timestamp of the trusted root that was in force.
    pub trust_root_signed_at: Option<DateTime<Utc>>,
}

/// Verification errors for an external receipt history checked against a
/// JSONL ledger.
#[derive(Debug, Error)]
pub enum ExternalReceiptVerifyError {
    /// The receipt history file could not be read.
    #[error("failed to read external anchor receipt history {path:?}: {source}")]
    ReadHistory {
        /// Receipt history path that was being read.
        path: PathBuf,
        /// I/O failure.
        source: std::io::Error,
    },
    /// The receipt history did not parse as repeated v1 records.
    #[error("invalid external anchor receipt history {path:?}: {source}")]
    Parse {
        /// Receipt history path that was being parsed.
        path: PathBuf,
        /// Parse failure.
        source: ExternalReceiptParseError,
    },
    /// One receipt referenced a chain-head hash that does not validate as a
    /// canonical [`LedgerAnchor`].
    #[error(
        "external anchor receipt {receipt_index} in {path:?} carries a malformed anchor: {source}"
    )]
    Anchor {
        /// Receipt history path that was being verified.
        path: PathBuf,
        /// 1-based receipt record index.
        receipt_index: usize,
        /// Anchor field validation failure.
        source: AnchorParseError,
    },
    /// The receipt's position-bound anchor failed to verify against the local ledger.
    #[error(
        "external anchor receipt {receipt_index} in {path:?} failed local anchor verification: {source}"
    )]
    AnchorVerify {
        /// Receipt history path that was being verified.
        path: PathBuf,
        /// 1-based receipt record index.
        receipt_index: usize,
        /// Local-ledger anchor verification failure.
        source: Box<AnchorVerifyError>,
    },
    /// The recomputed `anchor_text_sha256` did not match the receipt-declared value.
    #[error(
        "{invariant}: external anchor receipt {receipt_index} in {path:?} declared anchor_text_sha256 {declared} but local ledger recomputes {observed}"
    )]
    AnchorTextHashMismatch {
        /// Stable invariant token, equal to [`ANCHOR_TEXT_HASH_MISMATCH_INVARIANT`].
        invariant: &'static str,
        /// Receipt history path that was being verified.
        path: PathBuf,
        /// 1-based receipt record index.
        receipt_index: usize,
        /// Anchor-text hash declared by the receipt.
        declared: String,
        /// Anchor-text hash recomputed from the local ledger.
        observed: String,
    },
    /// The cached or embedded `trusted_root.json` is older than the
    /// operator-configured staleness window. Emits the stable
    /// [`TRUSTED_ROOT_STALE_INVARIANT`].
    #[error(
        "{invariant}: trusted_root.json (status={trust_root_status}) signed_at {signed_at:?} is stale beyond max_age {max_age:?} at now {now}"
    )]
    TrustedRootStale {
        /// Stable invariant token, equal to [`TRUSTED_ROOT_STALE_INVARIANT`].
        invariant: &'static str,
        /// Provenance token: [`EMBEDDED_ROOT_STATUS`] or [`CACHED_ROOT_STATUS`].
        trust_root_status: &'static str,
        /// Cache path that was inspected, if any.
        cache_path: Option<PathBuf>,
        /// Latest `validFor.start` observed in the active trust root.
        signed_at: Option<DateTime<Utc>>,
        /// Wall-clock used to compute staleness.
        now: DateTime<Utc>,
        /// Maximum age permitted by the operator policy.
        max_age: Duration,
    },
    /// The cached `trusted_root.json` could not be loaded — I/O or parse
    /// failure on the operator-supplied path. The embedded fallback path
    /// is selected by passing `None` for the cache; this variant only
    /// fires when a cache path was supplied AND the file existed.
    #[error("{invariant}: failed to load trusted_root.json from {path:?}: {source}")]
    TrustedRootIo {
        /// Stable invariant token, equal to [`TRUSTED_ROOT_PARSE_INVARIANT`].
        invariant: &'static str,
        /// Cache path that was being inspected.
        path: PathBuf,
        /// Underlying I/O / parse failure.
        source: Box<TrustedRootIoError>,
    },
}

/// Verify a v1 external anchor receipt history against the local JSONL
/// ledger using the **parser-only** rules, with the embedded trust root
/// and `Utc::now()` for the staleness gate.
///
/// For each receipt this enforces:
///
/// 1. The receipt envelope parses and the receipt is well-formed.
/// 2. The receipt's `(anchor_event_count, anchor_chain_head_hash)` pair
///    parses as a canonical [`LedgerAnchor`] and verifies against the
///    local ledger via [`verify_anchor`].
/// 3. SHA-256 over the canonical anchor text at that position matches
///    `anchor_text_sha256`. Mismatch returns
///    [`ExternalReceiptVerifyError::AnchorTextHashMismatch`] with the
///    stable [`ANCHOR_TEXT_HASH_MISMATCH_INVARIANT`] token.
/// 4. Monotonicity across the receipt history is enforced by
///    [`parse_external_receipt_history`] before any per-receipt check
///    runs.
/// 5. The active trusted root (embedded snapshot here, see
///    [`verify_external_receipts_with_options`] for cached refresh) is
///    not stale beyond [`DEFAULT_MAX_TRUST_ROOT_AGE`]. The staleness
///    gate fails closed with [`ExternalReceiptVerifyError::TrustedRootStale`].
///
/// **Out of scope today:** Rekor `SignedEntryTimestamp` verification and
/// OpenTimestamps `.ots` proof verification. A successful return from this
/// function carries `status = `[`PARSED_ONLY_VERIFICATION_STATUS`] to make
/// the deferred-authority surface explicit to operators.
pub fn verify_external_receipts(
    ledger_path: impl AsRef<Path>,
    receipts_path: impl Into<PathBuf>,
) -> Result<ExternalReceiptVerification, ExternalReceiptVerifyError> {
    verify_external_receipts_with_options(
        ledger_path,
        receipts_path,
        None,
        Utc::now(),
        DEFAULT_MAX_TRUST_ROOT_AGE,
    )
}

/// Same as [`verify_external_receipts`] but with the trust-root cache
/// path, wall clock, and staleness window injected by the caller.
///
/// `trust_root_cache` is `Some(path)` when the operator has refreshed
/// `trusted_root.json` via `cortex audit anchor refresh-trust`. When the
/// file is missing or unparseable, the embedded snapshot is the
/// fail-closed floor. `now` and `max_age` follow the ADR 0041 pattern of
/// caller-injected freshness inputs (no system clock buried in the trust
/// path) so test fixtures can pin both axes.
pub fn verify_external_receipts_with_options(
    ledger_path: impl AsRef<Path>,
    receipts_path: impl Into<PathBuf>,
    trust_root_cache: Option<&Path>,
    now: DateTime<Utc>,
    max_age: Duration,
) -> Result<ExternalReceiptVerification, ExternalReceiptVerifyError> {
    let receipts_path = receipts_path.into();
    let active = match active_trusted_root(trust_root_cache) {
        Ok(active) => active,
        Err(source) => {
            let path = trust_root_cache
                .map(Path::to_path_buf)
                .unwrap_or_else(|| PathBuf::from("<embedded>"));
            return Err(ExternalReceiptVerifyError::TrustedRootIo {
                invariant: TRUSTED_ROOT_PARSE_INVARIANT,
                path,
                source: Box::new(source),
            });
        }
    };
    // ADR 0013 staleness policy (council Decision #1; 2026-05-15
    // portfolio-extension fix on the 2026-05-12 footnote):
    //
    //   embedded + stale  -> warn-only, allow operation (operator may not
    //                        have refreshed yet; refusing here would brick
    //                        every first-time install)
    //   cached   + stale  -> fail closed (operator HAS refreshed once, the
    //                        refresh cadence has lapsed beyond max_age, so
    //                        external anchor authority cannot stand)
    //
    // Anchor field-choice (Bug J + portfolio extension): cached-path
    // staleness is anchored to the cache file's mtime, NOT the Sigstore
    // tlog signing-key activation date inside the JSON (the latter
    // rotates rarely so would make every release immediately stale).
    // The warn-only branch returns the active status verbatim so callers
    // still see `embedded_snapshot` and can surface the warning.
    let trust_root_status = active.status;
    let trust_root_signed_at = active.root.metadata_signed_at();
    if active.status == CACHED_ROOT_STATUS {
        let cache_path = active
            .cache_path
            .as_deref()
            .expect("CACHED_ROOT_STATUS implies a cache path was inspected");
        let anchor = TrustRootStalenessAnchor::cache_file_mtime(cache_path);
        match active.root.is_stale_at(now, max_age, anchor) {
            Ok(true) => {
                return Err(ExternalReceiptVerifyError::TrustedRootStale {
                    invariant: TRUSTED_ROOT_CACHE_STALE_INVARIANT,
                    trust_root_status,
                    cache_path: active.cache_path,
                    signed_at: trust_root_signed_at,
                    now,
                    max_age,
                });
            }
            Ok(false) => {}
            Err(TrustRootStalenessError::CacheFutureDated { .. }) => {
                // Prior F3 closure: future-dated cache mtime is a
                // dedicated bypass guard, not a parse / I/O failure.
                // Surface it as the `cache_future_dated` invariant so
                // operators and dashboards can pivot on a stable token.
                return Err(ExternalReceiptVerifyError::TrustedRootStale {
                    invariant: trusted_root::STABLE_INVARIANT_TRUSTED_ROOT_CACHE_FUTURE_DATED,
                    trust_root_status,
                    cache_path: active.cache_path,
                    signed_at: trust_root_signed_at,
                    now,
                    max_age,
                });
            }
            Err(source) => {
                return Err(ExternalReceiptVerifyError::TrustedRootIo {
                    invariant: TRUSTED_ROOT_PARSE_INVARIANT,
                    path: cache_path.to_path_buf(),
                    source: Box::new(TrustedRootIoError::Read {
                        path: cache_path.to_path_buf(),
                        source: std::io::Error::other(source.to_string()),
                    }),
                });
            }
        }
    }

    let text = std::fs::read_to_string(&receipts_path).map_err(|source| {
        ExternalReceiptVerifyError::ReadHistory {
            path: receipts_path.clone(),
            source,
        }
    })?;
    let receipts = parse_external_receipt_history(&text).map_err(|source| {
        ExternalReceiptVerifyError::Parse {
            path: receipts_path.clone(),
            source,
        }
    })?;

    // Note: `parse_external_receipt_history` already verified monotonicity
    // and that there is at least one receipt; this expect is structural.
    let mut latest_db_count = 0u64;
    let mut latest_receipt: Option<ExternalReceipt> = None;

    for (index, receipt) in receipts.iter().enumerate() {
        let record_index = index + 1;
        // Build a canonical anchor for the witnessed position. We do not
        // accept the receipt's chain head verbatim — we ask the local
        // ledger to confirm the position-hash pair, just like
        // `verify_anchor` does.
        let anchor = LedgerAnchor::new(
            receipt.submitted_at,
            receipt.anchor_event_count,
            receipt.anchor_chain_head_hash.clone(),
        )
        .map_err(|source| ExternalReceiptVerifyError::Anchor {
            path: receipts_path.clone(),
            receipt_index: record_index,
            source,
        })?;
        let verified = verify_anchor(ledger_path.as_ref(), &anchor).map_err(|source| {
            ExternalReceiptVerifyError::AnchorVerify {
                path: receipts_path.clone(),
                receipt_index: record_index,
                source: Box::new(source),
            }
        })?;
        let recomputed = sha256_hex(anchor.to_anchor_text().as_bytes());
        if recomputed != receipt.anchor_text_sha256 {
            return Err(ExternalReceiptVerifyError::AnchorTextHashMismatch {
                invariant: ANCHOR_TEXT_HASH_MISMATCH_INVARIANT,
                path: receipts_path,
                receipt_index: record_index,
                declared: receipt.anchor_text_sha256.clone(),
                observed: recomputed,
            });
        }
        latest_db_count = verified.db_count;
        latest_receipt = Some(receipt.clone());
    }

    let latest_receipt = latest_receipt.expect("parse_external_receipt_history returns non-empty");
    Ok(ExternalReceiptVerification {
        path: ledger_path.as_ref().to_path_buf(),
        receipts_path,
        db_count: latest_db_count,
        receipts_verified: receipts.len(),
        latest_receipt,
        status: PARSED_ONLY_VERIFICATION_STATUS,
        trust_root_status,
        trust_root_signed_at,
    })
}

/// Helper for callers (CLI, drill scripts, etc.) that need to construct a
/// stable, canonical `anchor_text_sha256` value for a given
/// [`LedgerAnchor`]. Equivalent to `sha256_hex(anchor.to_anchor_text())`.
#[must_use]
pub fn anchor_text_sha256(anchor: &LedgerAnchor) -> String {
    sha256_hex(anchor.to_anchor_text().as_bytes())
}

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

    fn sample_receipt(event_count: u64, sink: ExternalSink) -> ExternalReceipt {
        ExternalReceipt {
            sink,
            anchor_text_sha256: "0".repeat(SHA256_HEX_LEN),
            anchor_event_count: event_count,
            anchor_chain_head_hash: "a".repeat(BLAKE3_HEX_LEN),
            submitted_at: Utc.with_ymd_and_hms(2026, 5, 12, 18, 0, 0).unwrap(),
            sink_endpoint: "https://rekor.sigstore.dev".to_string(),
            receipt: serde_json::json!({"logIndex": 1, "uuid": "abc"}),
        }
    }

    #[test]
    fn parses_clean_record_round_trip() {
        let receipt = sample_receipt(7, ExternalSink::Rekor);
        let text = receipt.to_record_text().unwrap();
        assert!(text.starts_with(EXTERNAL_RECEIPT_FORMAT_HEADER_V1));
        let parsed = parse_external_receipt(&text).unwrap();
        assert_eq!(parsed, receipt);
    }

    #[test]
    fn rejects_unknown_sink_token() {
        let body = serde_json::json!({
            "sink": "unknown-sink",
            "anchor_text_sha256": "0".repeat(SHA256_HEX_LEN),
            "anchor_event_count": 1,
            "anchor_chain_head_hash": "a".repeat(BLAKE3_HEX_LEN),
            "submitted_at": "2026-05-12T18:00:00Z",
            "sink_endpoint": "https://example.invalid",
            "receipt": {},
        });
        let text = format!("{EXTERNAL_RECEIPT_FORMAT_HEADER_V1}\n{body}\n");
        let err = parse_external_receipt(&text).unwrap_err();
        match err {
            ExternalReceiptParseError::MalformedBody { reason } => {
                assert!(
                    reason.contains("unknown external anchor receipt sink"),
                    "{reason}"
                );
            }
            other => panic!("expected MalformedBody, got {other:?}"),
        }
    }

    #[test]
    fn rejects_missing_header() {
        let body = serde_json::to_string(&sample_receipt(1, ExternalSink::Rekor)).unwrap();
        let err = parse_external_receipt(&body).unwrap_err();
        assert!(matches!(
            err,
            ExternalReceiptParseError::UnknownFormatHeader { .. }
        ));
    }

    #[test]
    fn rejects_unknown_format_header() {
        let body = serde_json::to_string(&sample_receipt(1, ExternalSink::Rekor)).unwrap();
        let text = format!("# cortex-external-anchor-receipt-format: 2\n{body}\n");
        let err = parse_external_receipt(&text).unwrap_err();
        assert!(matches!(
            err,
            ExternalReceiptParseError::UnknownFormatHeader { .. }
        ));
    }

    #[test]
    fn rejects_missing_required_field() {
        let body = serde_json::json!({
            "sink": "rekor",
            "anchor_event_count": 1,
            "anchor_chain_head_hash": "a".repeat(BLAKE3_HEX_LEN),
            "submitted_at": "2026-05-12T18:00:00Z",
            "sink_endpoint": "https://example.invalid",
            "receipt": {},
        });
        let text = format!("{EXTERNAL_RECEIPT_FORMAT_HEADER_V1}\n{body}\n");
        let err = parse_external_receipt(&text).unwrap_err();
        match err {
            ExternalReceiptParseError::MalformedBody { reason } => {
                assert!(reason.contains("anchor_text_sha256"), "{reason}");
            }
            other => panic!("expected MalformedBody, got {other:?}"),
        }
    }

    #[test]
    fn rejects_invalid_hex_lengths() {
        let mut receipt = sample_receipt(1, ExternalSink::Rekor);
        receipt.anchor_text_sha256 = "abc".to_string();
        let body = serde_json::to_string(&receipt).unwrap();
        let text = format!("{EXTERNAL_RECEIPT_FORMAT_HEADER_V1}\n{body}\n");
        let err = parse_external_receipt(&text).unwrap_err();
        assert!(matches!(
            err,
            ExternalReceiptParseError::InvalidHexField {
                field: "anchor_text_sha256",
                ..
            }
        ));
    }

    #[test]
    fn rejects_trailing_content() {
        let body = serde_json::to_string(&sample_receipt(1, ExternalSink::Rekor)).unwrap();
        let text = format!("{EXTERNAL_RECEIPT_FORMAT_HEADER_V1}\n{body}\nextra\n");
        let err = parse_external_receipt(&text).unwrap_err();
        assert_eq!(err, ExternalReceiptParseError::TrailingContent);
    }

    #[test]
    fn rejects_none_sink_in_payload() {
        let body = serde_json::json!({
            "sink": "none",
            "anchor_text_sha256": "0".repeat(SHA256_HEX_LEN),
            "anchor_event_count": 1,
            "anchor_chain_head_hash": "a".repeat(BLAKE3_HEX_LEN),
            "submitted_at": "2026-05-12T18:00:00Z",
            "sink_endpoint": "https://example.invalid",
            "receipt": {},
        });
        let text = format!("{EXTERNAL_RECEIPT_FORMAT_HEADER_V1}\n{body}\n");
        let err = parse_external_receipt(&text).unwrap_err();
        assert!(matches!(err, ExternalReceiptParseError::UnknownSink { .. }));
    }

    #[test]
    fn parses_history_round_trip_with_monotonic_records() {
        let r1 = sample_receipt(1, ExternalSink::Rekor);
        let r2 = sample_receipt(3, ExternalSink::OpenTimestamps);
        let text = format!(
            "{}{}",
            r1.to_record_text().unwrap(),
            r2.to_record_text().unwrap()
        );
        let parsed = parse_external_receipt_history(&text).unwrap();
        assert_eq!(parsed, vec![r1, r2]);
    }

    #[test]
    fn history_rejects_non_monotonic_event_count() {
        let r1 = sample_receipt(5, ExternalSink::Rekor);
        let r2 = sample_receipt(2, ExternalSink::Rekor);
        let text = format!(
            "{}{}",
            r1.to_record_text().unwrap(),
            r2.to_record_text().unwrap()
        );
        let err = parse_external_receipt_history(&text).unwrap_err();
        assert!(matches!(
            err,
            ExternalReceiptParseError::NonMonotonic {
                receipt_index: 2,
                previous_event_count: 5,
                event_count: 2,
            }
        ));
    }

    #[test]
    fn history_rejects_truncated_record() {
        let err = parse_external_receipt_history(EXTERNAL_RECEIPT_FORMAT_HEADER_V1).unwrap_err();
        assert_eq!(err, ExternalReceiptParseError::MissingBody);
    }

    #[test]
    fn history_rejects_empty_input() {
        let err = parse_external_receipt_history("").unwrap_err();
        assert_eq!(err, ExternalReceiptParseError::MissingHeader);
    }

    #[test]
    fn sink_wire_tokens_are_stable() {
        assert_eq!(ExternalSink::None.as_wire_str(), "none");
        assert_eq!(ExternalSink::Rekor.as_wire_str(), "rekor");
        assert_eq!(ExternalSink::OpenTimestamps.as_wire_str(), "opentimestamps");
    }

    #[test]
    fn sink_from_wire_str_rejects_garbage() {
        let err = ExternalSink::from_wire_str("garbage").unwrap_err();
        assert!(matches!(err, ExternalReceiptParseError::UnknownSink { .. }));
    }

    // ---------- Slice 3: verify_external_receipts ----------

    use cortex_core::{Event, EventId, EventSource, EventType, SCHEMA_VERSION};
    use tempfile::tempdir;

    use crate::JsonlLog;

    fn ledger_event(seq: u64) -> Event {
        Event {
            id: EventId::new(),
            schema_version: SCHEMA_VERSION,
            observed_at: Utc.with_ymd_and_hms(2026, 5, 12, 18, 0, 0).unwrap(),
            recorded_at: Utc.with_ymd_and_hms(2026, 5, 12, 18, 0, 1).unwrap(),
            source: EventSource::User,
            event_type: EventType::UserMessage,
            trace_id: None,
            session_id: Some("ext-receipt".into()),
            domain_tags: vec![],
            payload: serde_json::json!({"seq": seq}),
            payload_hash: String::new(),
            prev_event_hash: None,
            event_hash: String::new(),
        }
    }

    fn build_ledger(count: u64) -> (tempfile::TempDir, std::path::PathBuf, Vec<String>) {
        let dir = tempdir().unwrap();
        let path = dir.path().join("events.jsonl");
        let mut log = JsonlLog::open(&path).unwrap();
        let mut heads = Vec::new();
        let policy = crate::append_policy_decision_test_allow();
        for seq in 0..count {
            heads.push(log.append(ledger_event(seq), &policy).unwrap());
        }
        (dir, path, heads)
    }

    fn make_canonical_receipt(
        timestamp: DateTime<Utc>,
        event_count: u64,
        chain_head: &str,
        sink: ExternalSink,
    ) -> ExternalReceipt {
        let anchor = LedgerAnchor::new(timestamp, event_count, chain_head.to_string()).unwrap();
        ExternalReceipt {
            sink,
            anchor_text_sha256: anchor_text_sha256(&anchor),
            anchor_event_count: event_count,
            anchor_chain_head_hash: chain_head.to_string(),
            submitted_at: timestamp,
            sink_endpoint: "https://rekor.sigstore.dev".to_string(),
            receipt: serde_json::json!({"logIndex": event_count, "uuid": "fixture"}),
        }
    }

    fn write_receipt_history(path: &Path, receipts: &[ExternalReceipt]) {
        let mut text = String::new();
        for receipt in receipts {
            text.push_str(&receipt.to_record_text().unwrap());
        }
        std::fs::write(path, text).unwrap();
    }

    #[test]
    fn clean_receipt_history_parses_and_verifies() {
        let (_dir, ledger, heads) = build_ledger(3);
        let receipts_path = ledger.parent().unwrap().join("EXTERNAL_ANCHOR_RECEIPTS");
        let r1 = make_canonical_receipt(
            Utc.with_ymd_and_hms(2026, 5, 12, 18, 5, 0).unwrap(),
            1,
            &heads[0],
            ExternalSink::Rekor,
        );
        let r2 = make_canonical_receipt(
            Utc.with_ymd_and_hms(2026, 5, 12, 18, 10, 0).unwrap(),
            3,
            &heads[2],
            ExternalSink::Rekor,
        );
        write_receipt_history(&receipts_path, &[r1, r2.clone()]);

        let verification = verify_external_receipts(&ledger, &receipts_path).unwrap();
        assert_eq!(verification.receipts_verified, 2);
        assert_eq!(verification.latest_receipt, r2);
        assert_eq!(verification.db_count, 3);
        assert_eq!(verification.status, PARSED_ONLY_VERIFICATION_STATUS);
    }

    #[test]
    fn tampered_anchor_text_hash_fails_closed_with_stable_invariant() {
        let (_dir, ledger, heads) = build_ledger(3);
        let receipts_path = ledger.parent().unwrap().join("EXTERNAL_ANCHOR_RECEIPTS");
        let mut r1 = make_canonical_receipt(
            Utc.with_ymd_and_hms(2026, 5, 12, 18, 5, 0).unwrap(),
            3,
            &heads[2],
            ExternalSink::Rekor,
        );
        r1.anchor_text_sha256 = "f".repeat(SHA256_HEX_LEN);
        write_receipt_history(&receipts_path, &[r1]);

        let err = verify_external_receipts(&ledger, &receipts_path).unwrap_err();
        match err {
            ExternalReceiptVerifyError::AnchorTextHashMismatch {
                invariant,
                receipt_index,
                ..
            } => {
                assert_eq!(invariant, ANCHOR_TEXT_HASH_MISMATCH_INVARIANT);
                assert_eq!(receipt_index, 1);
            }
            other => panic!("expected AnchorTextHashMismatch, got {other:?}"),
        }
    }

    #[test]
    fn tampered_anchor_chain_head_hash_fails_closed() {
        let (_dir, ledger, heads) = build_ledger(3);
        let receipts_path = ledger.parent().unwrap().join("EXTERNAL_ANCHOR_RECEIPTS");
        let mut r1 = make_canonical_receipt(
            Utc.with_ymd_and_hms(2026, 5, 12, 18, 5, 0).unwrap(),
            3,
            &heads[2],
            ExternalSink::Rekor,
        );
        // Replace with a valid-shape hash that does not match the ledger.
        r1.anchor_chain_head_hash = "0".repeat(BLAKE3_HEX_LEN);
        // Also resynth anchor_text_sha256 so the AnchorVerify branch
        // fires before the hash mismatch branch — verifies that the
        // local-anchor verification is the load-bearing check.
        let bogus_anchor = LedgerAnchor::new(
            r1.submitted_at,
            r1.anchor_event_count,
            r1.anchor_chain_head_hash.clone(),
        )
        .unwrap();
        r1.anchor_text_sha256 = anchor_text_sha256(&bogus_anchor);
        write_receipt_history(&receipts_path, &[r1]);

        let err = verify_external_receipts(&ledger, &receipts_path).unwrap_err();
        assert!(
            matches!(err, ExternalReceiptVerifyError::AnchorVerify { .. }),
            "got {err:?}"
        );
    }

    #[test]
    fn non_monotonic_receipt_history_fails_closed_before_anchor_check() {
        let (_dir, ledger, heads) = build_ledger(3);
        let receipts_path = ledger.parent().unwrap().join("EXTERNAL_ANCHOR_RECEIPTS");
        let r1 = make_canonical_receipt(
            Utc.with_ymd_and_hms(2026, 5, 12, 18, 5, 0).unwrap(),
            3,
            &heads[2],
            ExternalSink::Rekor,
        );
        let r2 = make_canonical_receipt(
            Utc.with_ymd_and_hms(2026, 5, 12, 18, 10, 0).unwrap(),
            1,
            &heads[0],
            ExternalSink::Rekor,
        );
        write_receipt_history(&receipts_path, &[r1, r2]);

        let err = verify_external_receipts(&ledger, &receipts_path).unwrap_err();
        match err {
            ExternalReceiptVerifyError::Parse { source, .. } => {
                assert!(matches!(
                    source,
                    ExternalReceiptParseError::NonMonotonic {
                        receipt_index: 2,
                        previous_event_count: 3,
                        event_count: 1,
                    }
                ));
            }
            other => panic!("expected Parse(NonMonotonic), got {other:?}"),
        }
    }

    #[test]
    fn missing_receipt_history_file_fails_closed() {
        let dir = tempdir().unwrap();
        let ledger = dir.path().join("events.jsonl");
        std::fs::write(&ledger, "").unwrap();
        let receipts_path = dir.path().join("missing-receipts");
        let err = verify_external_receipts(&ledger, &receipts_path).unwrap_err();
        assert!(matches!(
            err,
            ExternalReceiptVerifyError::ReadHistory { .. }
        ));
    }

    // ---------- Slice 4: trusted-root staleness gate ----------

    fn near_root_now() -> DateTime<Utc> {
        // Pin `now` close to the embedded trust root's latest tlog
        // activation so the staleness gate does not falsely fire when
        // the test wall clock drifts.
        let root = TrustedRoot::embedded().unwrap();
        let signed_at = root.metadata_signed_at().unwrap();
        signed_at + chrono::Duration::days(1)
    }

    fn build_receipts_fixture() -> (tempfile::TempDir, std::path::PathBuf, std::path::PathBuf) {
        let (dir, ledger, heads) = build_ledger(3);
        let receipts_path = ledger.parent().unwrap().join("EXTERNAL_ANCHOR_RECEIPTS");
        let r1 = make_canonical_receipt(
            Utc.with_ymd_and_hms(2026, 5, 12, 18, 5, 0).unwrap(),
            3,
            &heads[2],
            ExternalSink::Rekor,
        );
        write_receipt_history(&receipts_path, &[r1]);
        (dir, ledger, receipts_path)
    }

    #[test]
    fn fresh_cached_root_allows_verification() {
        let (dir, ledger, receipts_path) = build_receipts_fixture();
        let trust_root_path = dir.path().join("trusted_root.json");
        TrustedRoot::embedded()
            .unwrap()
            .write_atomic(&trust_root_path)
            .unwrap();

        let now = near_root_now();
        // Prior F3 closure (2026-05-13): pin the cache file's mtime
        // back to the injected `now`. Without this, the cache mtime
        // (real wall-clock at write time, ~2026-05-13) is ahead of
        // the injected `now` (`signed_at + 1 day` ~2025-09-24) by
        // months, and the future-dated bypass guard correctly fires.
        // We are NOT trying to exercise that guard here; we are
        // pinning the standard "fresh cache mtime, fresh now" path.
        let mtime_systemtime = std::time::SystemTime::UNIX_EPOCH
            + std::time::Duration::from_secs(now.timestamp() as u64);
        std::fs::File::options()
            .write(true)
            .open(&trust_root_path)
            .unwrap()
            .set_modified(mtime_systemtime)
            .expect("set mtime");
        let verification = verify_external_receipts_with_options(
            &ledger,
            &receipts_path,
            Some(&trust_root_path),
            now,
            DEFAULT_MAX_TRUST_ROOT_AGE,
        )
        .expect("fresh cached root verifies");
        assert_eq!(verification.trust_root_status, CACHED_ROOT_STATUS);
        assert!(verification.trust_root_signed_at.is_some());
        assert_eq!(verification.status, PARSED_ONLY_VERIFICATION_STATUS);
    }

    #[test]
    fn cached_root_older_than_31_days_fails_closed_with_cache_stale_invariant() {
        let (dir, ledger, receipts_path) = build_receipts_fixture();
        let trust_root_path = dir.path().join("trusted_root.json");
        TrustedRoot::embedded()
            .unwrap()
            .write_atomic(&trust_root_path)
            .unwrap();

        // 2026-05-15 portfolio extension of Bug J: cached-path staleness
        // is anchored to file mtime, NOT the Sigstore tlog activation
        // inside the JSON. Set the cache file's mtime 31 days in the
        // past so the gate fires on the operator-meaningful datum.
        let now = Utc::now();
        let old_mtime = now - chrono::Duration::days(31);
        let mtime_systemtime = std::time::SystemTime::UNIX_EPOCH
            + std::time::Duration::from_secs(old_mtime.timestamp() as u64);
        std::fs::File::options()
            .write(true)
            .open(&trust_root_path)
            .unwrap()
            .set_modified(mtime_systemtime)
            .expect("set mtime");

        let err = verify_external_receipts_with_options(
            &ledger,
            &receipts_path,
            Some(&trust_root_path),
            now,
            DEFAULT_MAX_TRUST_ROOT_AGE,
        )
        .unwrap_err();
        match err {
            ExternalReceiptVerifyError::TrustedRootStale {
                invariant,
                trust_root_status,
                ..
            } => {
                assert_eq!(invariant, TRUSTED_ROOT_CACHE_STALE_INVARIANT);
                assert_eq!(trust_root_status, CACHED_ROOT_STATUS);
            }
            other => panic!("expected TrustedRootStale, got {other:?}"),
        }
    }

    #[test]
    fn cached_root_with_fresh_mtime_passes_even_when_metadata_old() {
        // 2026-05-15 portfolio extension of Bug J: a freshly-written
        // cache MUST pass the staleness gate even when the embedded
        // JSON's tlog-activation date is months old. This is the
        // structural defense against the metadata_signed_at-derived
        // staleness bug.
        let (dir, ledger, receipts_path) = build_receipts_fixture();
        let trust_root_path = dir.path().join("trusted_root.json");
        TrustedRoot::embedded()
            .unwrap()
            .write_atomic(&trust_root_path)
            .unwrap();
        // Wall clock 1 year past the embedded snapshot's tlog
        // activation. Under the buggy metadata_signed_at anchor this
        // would have fired stale; under the fixed mtime anchor it does
        // not provided the cache file's mtime is also pinned forward.
        let now = TrustedRoot::embedded()
            .unwrap()
            .metadata_signed_at()
            .unwrap()
            + chrono::Duration::days(365);
        // Pin cache mtime to the simulated `now` so the staleness gate
        // sees age=0 instead of negative drift between wall-clock
        // injection and real fs mtime.
        let mtime_systemtime = std::time::SystemTime::UNIX_EPOCH
            + std::time::Duration::from_secs(now.timestamp() as u64);
        std::fs::File::options()
            .write(true)
            .open(&trust_root_path)
            .unwrap()
            .set_modified(mtime_systemtime)
            .expect("set mtime");
        let verification = verify_external_receipts_with_options(
            &ledger,
            &receipts_path,
            Some(&trust_root_path),
            now,
            DEFAULT_MAX_TRUST_ROOT_AGE,
        )
        .expect("fresh cache mtime must pass the staleness gate");
        assert_eq!(verification.trust_root_status, CACHED_ROOT_STATUS);
    }

    #[test]
    fn missing_cache_falls_back_to_embedded_and_allows_even_when_stale() {
        let (dir, ledger, receipts_path) = build_receipts_fixture();
        let missing_cache = dir.path().join("nonexistent-trusted_root.json");
        // Step the clock far past any plausible embedded activation.
        let now = Utc.with_ymd_and_hms(2099, 1, 1, 0, 0, 0).unwrap();

        let verification = verify_external_receipts_with_options(
            &ledger,
            &receipts_path,
            Some(&missing_cache),
            now,
            DEFAULT_MAX_TRUST_ROOT_AGE,
        )
        .expect("missing cache + stale embedded still allows (warn-only)");
        assert_eq!(verification.trust_root_status, EMBEDDED_ROOT_STATUS);
    }

    #[test]
    fn unparseable_cache_fails_closed_with_parse_invariant() {
        let (dir, ledger, receipts_path) = build_receipts_fixture();
        let trust_root_path = dir.path().join("trusted_root.json");
        std::fs::write(&trust_root_path, b"this is not valid json").unwrap();

        let now = near_root_now();
        let err = verify_external_receipts_with_options(
            &ledger,
            &receipts_path,
            Some(&trust_root_path),
            now,
            DEFAULT_MAX_TRUST_ROOT_AGE,
        )
        .unwrap_err();
        match err {
            ExternalReceiptVerifyError::TrustedRootIo { invariant, .. } => {
                assert_eq!(invariant, TRUSTED_ROOT_PARSE_INVARIANT);
            }
            other => panic!("expected TrustedRootIo, got {other:?}"),
        }
    }

    /// Prior F3 closure
    /// (`docs/reviews/CODE_REVIEW_2026-05-12_post_fd779d7.md`): the
    /// audit-verify path used to silently pass when the cached
    /// `trusted_root.json` had a future-dated mtime. The freshness
    /// gate now refuses with the cache-future-dated invariant.
    #[test]
    fn cached_root_with_future_dated_mtime_fails_closed_with_future_dated_invariant() {
        let (dir, ledger, receipts_path) = build_receipts_fixture();
        let trust_root_path = dir.path().join("trusted_root.json");
        TrustedRoot::embedded()
            .unwrap()
            .write_atomic(&trust_root_path)
            .unwrap();

        let now = near_root_now();
        // Touch the cache 70 years into the future — the original
        // `touch -d 2099-01-01` attack shape.
        let future = now + chrono::Duration::days(365 * 70);
        let future_systemtime = std::time::SystemTime::UNIX_EPOCH
            + std::time::Duration::from_secs(future.timestamp() as u64);
        std::fs::File::options()
            .write(true)
            .open(&trust_root_path)
            .unwrap()
            .set_modified(future_systemtime)
            .expect("set mtime");

        let err = verify_external_receipts_with_options(
            &ledger,
            &receipts_path,
            Some(&trust_root_path),
            now,
            DEFAULT_MAX_TRUST_ROOT_AGE,
        )
        .unwrap_err();
        match err {
            ExternalReceiptVerifyError::TrustedRootStale {
                invariant,
                trust_root_status,
                ..
            } => {
                assert_eq!(
                    invariant,
                    trusted_root::STABLE_INVARIANT_TRUSTED_ROOT_CACHE_FUTURE_DATED
                );
                assert_eq!(trust_root_status, CACHED_ROOT_STATUS);
            }
            other => panic!("expected TrustedRootStale with cache_future_dated, got {other:?}"),
        }
    }
}