khive-runtime 0.4.0

//! Write-time secret detection gate.
//!
//! Scans caller-supplied content strings before any storage write.  A match
//! causes a hard `RuntimeError::SecretDetected` that names the detector and
//! carries a masked excerpt — it never echoes the full candidate back.
//!
//! Scope: **credentials only** — API keys, tokens, private keys, passwords,
//! and connection strings with embedded credentials.  General PII such as
//! email addresses, phone numbers, and company names is intentionally NOT
//! blocked; those are normal knowledge-graph content.
//!
//! Detection is layered, cheap-first:
//!
//! 1. **Known-prefix / known-shape patterns** — AWS AKIA/ASIA, GitHub tokens,
//!    OpenAI `sk-proj-`, Anthropic `sk-ant-`, Stripe live keys, Fly.io tokens,
//!    Vercel secrets, Slack `xox*`, JWT triples, PEM private-key headers,
//!    Age secret keys, URL userinfo (`scheme://user:pass@`).
//!    Bare `sk-` is also checked but only when NOT followed by a known safe
//!    word boundary (e.g. `sk-learn`, `sk-image`).
//! 2. **High-entropy token heuristic** — base64/hex/base64url runs ≥ 24 chars
//!    near a trigger word (key, secret, password, credential, bearer, auth,
//!    apikey, api_key, access_key, private_key).  The word `token` alone is NOT
//!    a trigger to avoid blocking `tokenizer_*`, `token_count`, etc.
//!
//! Allowlist (false-positive suppression) — **all of the following are
//! prose-context exemptions, not unconditional passes: a credential trigger
//! word in the surrounding window always dominates.** A UUID or a
//! sha-prefixed content hash sitting directly beside "api_key"/"secret"/"auth"
//! is exactly as ambiguous as any other high-entropy candidate and falls
//! through to explicit detection instead of being silently allowed.
//! - Pure hex strings (sha256, git SHA) — passed when not near a trigger.
//! - UUID canonical form (`xxxxxxxx-xxxx-…`) — passed when not near a trigger.
//! - Base64/base64url content hashes with an explicit `sha<N>-` prefix (SRI
//!   hashes, npm lockfile integrity) — passed when not near a trigger and not
//!   preceded by a known-vendor prefix.  Bare base64 tokens without the
//!   `sha<N>-` prefix are NOT passed.
//! - Strings that are entirely ASCII punctuation/whitespace (e.g. code) — not
//!   subject to the entropy heuristic, only the literal-prefix checks apply.
//! - Non-ASCII characters (CJK prose, accented text, emoji) act as token
//!   delimiters for the entropy heuristic: only maximal ASCII runs are
//!   entropy-checked.  Real base64/hex/base64url credentials are ASCII, and
//!   `shannon_entropy` runs over UTF-8 bytes — multibyte codepoints inflate the
//!   byte-wise entropy and false-positive on natural-language non-Latin content.
//!   Treating non-ASCII as a delimiter (rather than skipping any whitespace
//!   token that merely contains it) keeps CJK prose unflagged while still
//!   catching an ASCII credential glued to CJK text/punctuation/fullwidth
//!   whitespace.  The literal-prefix checks (Layer 1) treat any
//!   non-ASCII-alphanumeric char (CJK, accented text, emoji) as a token
//!   boundary, so a known-prefix secret is caught whether the adjacent
//!   non-ASCII sits before the prefix (`数据AKIA…`) or after it (`AKIA…数据`).
//! - Structured identifiers: a token is only considered for this exemption
//!   when it contains at least one of `/`, `-`, `_`, or `.` (the gate); it is
//!   then decomposed into maximal alphanumeric runs by splitting on *every*
//!   non-alphanumeric character (not just the four gating separators — any
//!   other ASCII punctuation glued into the same whitespace token, e.g. a
//!   stray `:` or `,`, also acts as a run boundary).  A token exempts when it
//!   decomposes into two or more such runs and every run is letters-then-digits
//!   or pure digits, at most 24 chars long, with a low case-transition density.
//!   This covers content like `fable-ops/ADR-DRAFT-adr079.md` or
//!   `local workspace artifact`, which is otherwise
//!   indistinguishable from a high-entropy secret once glued into one
//!   whitespace token.  Random base64/base62 secrets do not decompose this
//!   way: their case and digit placement is effectively uniform rather than
//!   word-shaped, so a hyphenated or underscored secret still fails this
//!   check and remains subject to the entropy heuristic below.
//!
//!   **This exemption applies ONLY outside an explicit credential trigger
//!   context.** Signals that measure Shannon entropy over an attacker-chosen
//!   run boundary (e.g. requiring a trailing file extension, or an average
//!   per-run letter entropy below a threshold) are not sound near a trigger
//!   word: an attacker who controls where a credential's separators fall can
//!   always choose run lengths whose entropy reads no higher than an ordinary
//!   short English path segment, since the measure only sees a
//!   character-frequency histogram, never word semantics. So near a trigger
//!   word, a structured-identifier-shaped token gets no exemption at all and
//!   falls through to the entropy heuristic like any other token. This is an
//!   accepted false-positive tradeoff on a small number of genuine
//!   paths/doc-slugs that happen to sit near a trigger word AND read above
//!   the entropy threshold on their own — see
//!   `accepted_false_positive_adr_draft_path_near_trigger` and its siblings
//!   for the specific repro cases this blocks, and the call site in
//!   `check_entropy_heuristic`.
//!
//! Trigger-word matching only fires on genuine mentions, not substring
//! collisions: bare trigger words (`key`, `secret`, `password`, `passwd`,
//! `credential`, `bearer`, `auth`, `apikey`) are matched at a word boundary
//! (`contains_bounded_word`), so `auth` does not fire inside `authorized` or
//! `authentication`, nor `key` inside `monkey`/`keyword`. The three compound
//! entries that already embed an underscore (`api_key`, `access_key`,
//! `private_key`) are matched as a plain substring instead, since the
//! underscore already disambiguates them and word-boundary matching would
//! only weaken them (e.g. `secret_access_key` no longer needs the bare
//! `secret`/`key` matches once `access_key` fires on its own).
//!
//! A structured-identifier-shaped token sitting near a **genuinely standalone**
//! trigger word (e.g. `auth work saved at .../repo-audit.md`, where `auth` is
//! an actual topical mention rather than a substring collision) is an accepted
//! false positive: no window-narrowing or exemption-widening scheme survives
//! the adversarial regression corpus without also reopening a real bypass,
//! because the caller (or an attacker) fully controls the prose between a
//! trigger word and a payload: narrowing `TRIGGER_WINDOW` or reinstating the
//! structured-identifier exemption near "bare" trigger mentions both fail the
//! same known bypass strings that motivated closing them.
//!
//! The caller-visible block message (`SecretMatch`'s `Display` impl) also
//! carries actionable guidance (`block_guidance`) to split or reword the
//! flagged token.
//!
//! The word-boundary rule above treats underscore as a BOUNDARY for bare
//! `TRIGGER_WORDS` (`contains_bounded_word`): deliberately different from
//! `has_standalone_token`'s rule for the word `token`, which treats
//! underscore as a continuation so `tokenizer`/`next_token`/`token_count`
//! stay exempt. Treating underscore as a boundary for the bare set is what
//! lets common underscore-joined credential-config compounds keep firing:
//! `SECRET_KEY=...` (Django/Flask-style config), `auth_token=...`,
//! `session_secret_...`, `signing_key=...` all match on the `secret`/`key`/
//! `auth` half even though none of them is in `COMPOUND_TRIGGER_WORDS`. This
//! is implemented by parameterizing the boundary rule (`contains_word`'s
//! `underscore_is_word_char` argument) rather than sharing one rule between
//! the two callers.
//!
//! A production-corpus replay harness (`corpus_replay`, `#[ignore]`d, run via
//! `KHIVE_REPLAY_DB=<path> cargo test ... -- --ignored --nocapture`) measures
//! the detector's block rate against real note/entity content; see the
//! harness's own output for current numbers rather than a point-in-time count
//! here, which would drift as the corpus changes.

use crate::error::{RuntimeError, RuntimeResult};

// ─── Public API ──────────────────────────────────────────────────────────────

/// Returned when a write would store credential-looking content.
///
/// Carries the detector name and a masked excerpt (`first6...Nchars`).  The
/// full candidate is never stored in the error.
#[derive(Debug, Clone, PartialEq, Eq)]
pub struct SecretMatch {
    /// Human-readable name of the detector that fired.
    pub detector: &'static str,
    /// `first6...N` — the first 6 chars of the match followed by the total length.
    pub masked: String,
}

impl std::fmt::Display for SecretMatch {
    fn fmt(&self, f: &mut std::fmt::Formatter<'_>) -> std::fmt::Result {
        write!(
            f,
            "content matches secret pattern {} at masked excerpt {}. {}",
            self.detector,
            self.masked,
            block_guidance(self.detector)
        )
    }
}

/// Actionable, caller-visible guidance for a hard block, keyed by detector
/// name. If the content genuinely is a credential, remove it. If it
/// is not — the common case for the detectors below, which key off SHAPE
/// near a trigger word rather than a known credential prefix — the fix is to
/// break up the flagged token so it no longer reads as one contiguous
/// high-entropy value: put it on its own line away from words like
/// key/secret/auth/token, or insert a space/punctuation inside a long path or
/// identifier (e.g. `workspaces / 20260705 / topic` instead of one glued
/// token).
fn block_guidance(detector: &'static str) -> &'static str {
    match detector {
        "high-entropy-token"
        | "uuid-near-trigger"
        | "content-hash-near-trigger"
        | "hex-credential-token" => {
            "If this is a real credential, remove it before writing. If it is not \
             (e.g. a file path, UUID, or hash that happens to sit near a word like \
             key/secret/auth/token), reword so the token is not glued directly next \
             to that word — e.g. move it to its own line, or insert a space or word \
             between them."
        }
        _ => {
            "If this is a real credential, remove it before writing; store secrets \
              in an env var or secrets manager instead."
        }
    }
}

/// Hard-block content from being written.
///
/// Returns `Err(RuntimeError::SecretDetected)` on the first match found, or
/// `Ok(())` if no secret pattern fires.
pub fn check(content: &str) -> RuntimeResult<()> {
    if let Some(m) = scan(content) {
        return Err(RuntimeError::SecretDetected(m));
    }
    Ok(())
}

/// Recursively scan a JSON value for credential-shaped strings.
///
/// Walks every string leaf (object values, array elements, nested objects).
/// Returns `Err(RuntimeError::SecretDetected)` on the first match found.
/// `None` / null / numeric / boolean JSON values are skipped.
pub fn check_json(value: &serde_json::Value) -> RuntimeResult<()> {
    scan_json_value(value)
}

/// Scan a string-tagged slice (entity/note tags).
///
/// Each tag string is scanned individually.
pub fn check_tags(tags: &[String]) -> RuntimeResult<()> {
    for tag in tags {
        check(tag)?;
    }
    Ok(())
}

fn scan_json_value(value: &serde_json::Value) -> RuntimeResult<()> {
    match value {
        serde_json::Value::String(s) => check(s),
        serde_json::Value::Array(arr) => {
            for v in arr {
                scan_json_value(v)?;
            }
            Ok(())
        }
        serde_json::Value::Object(map) => {
            for (k, v) in map {
                // Scan both the key (a credential can appear as a JSON key name)
                // and the value recursively.
                check(k)?;
                scan_json_value(v)?;
            }
            Ok(())
        }
        _ => Ok(()),
    }
}

// ─── Scanner ─────────────────────────────────────────────────────────────────

/// Marker substituted for a detected secret span by [`mask_secrets`].
const REDACTION_MARKER: &str = "***MASKED***";

/// Return the LEFTMOST secret in `text` as `(matched_slice, detector)`.
///
/// The matched slice borrows from `text`, so the caller can recover its byte
/// span via pointer arithmetic — this is what lets [`mask_secrets`] redact in
/// place while [`scan`] only needs the masked excerpt.
///
/// "Leftmost" (smallest start offset), NOT first-by-detector-priority, is the
/// load-bearing contract: [`mask_secrets`] copies the text *before* each match
/// verbatim, so a non-leftmost match would leak an earlier secret detected by a
/// lower-priority detector (e.g. an `sk-ant-` key sitting to the left of a
/// `ghp_` token). Both detector layers are folded through [`keep_leftmost`].
fn scan_match(text: &str) -> Option<(&str, &'static str)> {
    scan_from(text, 0)
}

/// Like [`scan_match`], but only returns secrets whose span starts at or after
/// `from`, while still evaluating Layer-2 trigger context against the FULL
/// `text`. [`mask_secrets`] calls this with an advancing `from` so that an
/// entropy token is detected even when its only trigger word sits to the left of
/// an already-redacted earlier secret. Layer-1 known patterns are context-free,
/// so scanning the `&text[from..]` suffix is equivalent; offsets recovered via
/// pointer arithmetic against the original `text` base stay absolute.
fn scan_from(text: &str, from: usize) -> Option<(&str, &'static str)> {
    let base = text.as_ptr() as usize;
    // Layer 1: known prefix / shape patterns. Context-free → suffix scan; the
    // returned slice still borrows from the same allocation, so its absolute
    // offset is `slice.as_ptr() - base`.
    let mut best = check_known_patterns(&text[from..]);
    // Layer 2: entropy heuristic on long tokens near trigger words. Evaluated
    // over the full text (so left-of-`from` trigger words count) but only tokens
    // at offset >= from are returned; kept only if left of the best known match.
    keep_leftmost(&mut best, check_entropy_heuristic(text, from), base);
    best
}

/// Replace `best` with `cand` when `cand` starts earlier in the original text
/// (`base` is the start address of that text). On a tie the incumbent wins, so
/// callers offer more-specific detectors first. This is what makes
/// [`check_known_patterns`] and [`scan_match`] return the leftmost secret span
/// rather than the first detector that happens to match anywhere.
fn keep_leftmost<'a>(
    best: &mut Option<(&'a str, &'static str)>,
    cand: Option<(&'a str, &'static str)>,
    base: usize,
) {
    if let Some((slice, name)) = cand {
        let start = slice.as_ptr() as usize - base;
        let replace = match *best {
            Some((incumbent, _)) => start < (incumbent.as_ptr() as usize - base),
            None => true,
        };
        if replace {
            *best = Some((slice, name));
        }
    }
}

/// Return the first `SecretMatch` found in `text`, or `None`.
fn scan(text: &str) -> Option<SecretMatch> {
    scan_match(text).map(|(slice, detector)| build_match(detector, slice))
}

/// Redact every detected secret span in `text`, replacing each with
/// `***MASKED***`.
///
/// This is the masking counterpart to [`check`]: where `check` hard-blocks a
/// write on the first match, `mask_secrets` is for content that must be STORED
/// with credentials stripped (the session mirror). A transcript line cannot be
/// rejected wholesale, so each credential span is replaced in place while the
/// surrounding prose is preserved. It reuses the SAME canonical detector set as
/// `check`/`scan`, so callers must never maintain a second, weaker masker.
///
/// Returns `Cow::Borrowed` when no secret is present (the common case), avoiding
/// an allocation. Spans are discovered left to right against the ORIGINAL text
/// via `scan_from`: each scan advances a `from` cursor past the previous span
/// but always evaluates trigger context over the full input. This closes the
/// entropy-context gap — a high-entropy value whose only trigger word sits to
/// the left of an earlier-redacted secret is still detected, because the trigger
/// window is never sliced away. The known-prefix detectors (real API keys:
/// `sk-ant-`, `sk-proj-`, `AKIA`/`ASIA`, GitHub, Stripe, …) are context-free and
/// matched the same way.
pub fn mask_secrets(text: &str) -> std::borrow::Cow<'_, str> {
    let base = text.as_ptr() as usize;
    // Collect every secret span (absolute byte offsets into `text`) before
    // writing any output, so trigger-context detection always sees the original
    // string rather than the suffix after the previous redaction.
    let mut spans: Vec<(usize, usize)> = Vec::new();
    let mut from = 0;
    while from < text.len() {
        match scan_from(text, from) {
            Some((sub, _detector)) => {
                let start = sub.as_ptr() as usize - base;
                // The prefix detectors return whitespace-delimited tokens, so a
                // credential glued to structural punctuation (JSON quotes/braces,
                // sentence commas) carries that trailing punctuation into the
                // match. Trim a conservative trailing set that can never be part
                // of a credential, so redacting does not consume surrounding JSON
                // or prose structure. `=` `/` `+` `.` `-` `_` are intentionally
                // NOT trimmed — they are valid base64/JWT/key characters.
                let core_len = sub
                    .trim_end_matches(['"', '\'', '`', '}', ']', ')', ',', ';'])
                    .len();
                let end = start + core_len.max(1);
                spans.push((start, end));
                // `scan_from` only returns matches with start >= from, and `end`
                // is strictly greater than `start`, so `from` strictly advances.
                from = end;
            }
            None => break,
        }
    }
    if spans.is_empty() {
        return std::borrow::Cow::Borrowed(text);
    }
    let mut out = String::with_capacity(text.len());
    let mut cursor = 0;
    for (start, end) in spans {
        // Spans are non-overlapping and ascending (each starts at/after the prior
        // `end`); `max(cursor)` is a defensive guard, never load-bearing.
        let start = start.max(cursor);
        out.push_str(&text[cursor..start]);
        out.push_str(REDACTION_MARKER);
        cursor = end.max(cursor);
    }
    out.push_str(&text[cursor..]);
    std::borrow::Cow::Owned(out)
}

// ─── Layer 1: known patterns ─────────────────────────────────────────────────

/// Each entry: (detector_name, needle, min_total_token_len).
///
/// The needle must appear as a word-boundary-adjacent prefix in the token.
/// `min_total_token_len` is the minimum length the token (needle + remainder)
/// must have — prevents the prefix alone triggering without a payload.
const PREFIX_DETECTORS: &[(&str, &str, usize)] = &[
    // AWS
    ("aws-access-key-id", "AKIA", 20),
    ("aws-access-key-id", "ASIA", 20),
    // GitHub tokens: personal-access (ghp_), OAuth (gho_), GitHub App
    // user-to-server (ghu_), server-to-server (ghs_), refresh (ghr_), and the
    // fine-grained PAT (github_pat_). All but github_pat_ share the gh*_ + 36+
    // base62 shape.
    ("github-token", "ghp_", 36),
    ("github-token", "gho_", 36),
    ("github-token", "ghu_", 36),
    ("github-token", "ghs_", 36),
    ("github-token", "ghr_", 36),
    ("github-token", "github_pat_", 20),
    // OpenAI
    ("openai-api-key", "sk-proj-", 40),
    // NOTE: bare "sk-" also matches Anthropic/Stripe below; put it last so
    // the more-specific detectors fire first when both would match.
    // Anthropic
    ("anthropic-api-key", "sk-ant-", 20),
    // Stripe live keys
    ("stripe-secret-key", "sk_live_", 30),
    ("stripe-restricted-key", "rk_live_", 30),
    // Fly.io (fm2_ prefix only — FlyV1 handled separately because it embeds a space)
    ("fly-token", "fm2_", 20),
    // Vercel
    ("vercel-token", "vercel_", 20),
    // Slack
    ("slack-token", "xoxb-", 40),
    ("slack-token", "xoxa-", 40),
    ("slack-token", "xoxp-", 40),
    ("slack-token", "xoxr-", 40),
    ("slack-token", "xoxs-", 40),
    // Age secret key
    ("age-secret-key", "AGE-SECRET-KEY-", 60),
];

/// Known safe compound words that start with `sk-` but are not credentials.
/// E.g. scikit-learn slugs such as `sk-learn`, `sk-image`, `sk-lego`.
const SK_SAFE_PREFIXES: &[&str] = &["sk-learn", "sk-image", "sk-lego", "sk-base", "sk-misc"];

/// Shape-based patterns checked with custom logic.
///
/// Returns the LEFTMOST match across every detector (see [`keep_leftmost`]). The
/// detectors are still offered in priority order, so two detectors that match at
/// the SAME offset (e.g. bare `sk-` and the more-specific `sk-ant-`) resolve to
/// the first-offered one.
fn check_known_patterns(text: &str) -> Option<(&str, &'static str)> {
    let base = text.as_ptr() as usize;
    let mut best: Option<(&str, &'static str)> = None;

    // --- Prefix patterns ---
    for &(name, needle, min_len) in PREFIX_DETECTORS {
        keep_leftmost(
            &mut best,
            find_prefix_token(text, needle, min_len).map(|m| (m, name)),
            base,
        );
    }

    // --- Bare `sk-` (after all more-specific sk- detectors above) ---
    // Require length ≥ 30 AND exclude known safe scikit/library compound words.
    if let Some(token) = find_prefix_token(text, "sk-", 30) {
        if !SK_SAFE_PREFIXES.iter().any(|safe| token.starts_with(safe)) {
            keep_leftmost(&mut best, Some((token, "openai-api-key")), base);
        }
    }

    // --- Fly.io FlyV1 token: "FlyV1 <base64-payload>" ---
    // The format embeds a space, so the generic prefix extractor (which stops at
    // whitespace) cannot measure the combined length.  Check for `FlyV1 ` followed
    // by ≥ 4 non-whitespace characters as the payload.
    if let Some(pos) = text.find("FlyV1 ") {
        let at_boundary = pos == 0 || {
            text[..pos]
                .chars()
                .next_back()
                .is_none_or(|c| !c.is_ascii_alphanumeric())
        };
        if at_boundary {
            let payload_start = pos + 6; // skip "FlyV1 "
            let payload = extract_token(&text[payload_start..]);
            if payload.len() >= 4 {
                let candidate = &text[pos..payload_start + payload.len()];
                keep_leftmost(&mut best, Some((candidate, "fly-token")), base);
            }
        }
    }

    // --- PEM private key block ---
    // "-----BEGIN <TYPE> PRIVATE KEY-----"
    if text.contains("-----BEGIN") && text.contains("PRIVATE KEY-----") {
        if let Some(pos) = text.find("-----BEGIN") {
            // Measure only the key block itself (up to END marker or end-of-string),
            // not the rest of the surrounding text, so build_match reports the
            // block length rather than the remaining string length.
            let block_end = text[pos..]
                .find("-----END")
                .map(|rel| {
                    text[pos + rel..]
                        .find('\n')
                        .map(|l| pos + rel + l + 1)
                        .unwrap_or(text.len())
                })
                .unwrap_or(text.len());
            let excerpt = &text[pos..block_end];
            keep_leftmost(&mut best, Some((excerpt, "pem-private-key")), base);
        }
    }

    // --- JWT triple: eyJ...eyJ...eyJ (header.payload.signature) ---
    // A JWT starts with "eyJ" (base64url of `{"`) and has exactly two dots.
    keep_leftmost(&mut best, find_jwt(text).map(|m| (m, "jwt")), base);

    // --- URL userinfo: scheme://user:pass@host ---
    keep_leftmost(
        &mut best,
        find_url_userinfo(text).map(|m| (m, "url-userinfo")),
        base,
    );

    best
}

/// Locate the first token in `text` that starts with `needle` and has a
/// total length >= `min_len`.  Returns a slice of the full token on match.
fn find_prefix_token<'a>(text: &'a str, needle: &str, min_len: usize) -> Option<&'a str> {
    let mut start = 0;
    while let Some(rel) = text[start..].find(needle) {
        let abs = start + rel;
        // Require that the needle starts at a token boundary (start-of-string
        // or preceded by a non-ASCII-alphanumeric char).  The needles are ASCII,
        // so only an ASCII alphanumeric can be a real continuation of the same
        // token; CJK/accented text (which Rust counts as `is_alphanumeric`) must
        // act as a delimiter, else a secret glued to non-Latin prose (`数据AKIA…`)
        // is missed.
        let at_boundary = abs == 0 || {
            let prev = text[..abs].chars().next_back().unwrap_or(' ');
            !prev.is_ascii_alphanumeric()
        };
        if at_boundary {
            let token = extract_token(&text[abs..]);
            if token.len() >= min_len {
                return Some(token);
            }
        }
        start = abs + needle.len().max(1);
    }
    None
}

/// Scan for a JWT pattern: at least two "eyJ" segments separated by a `.`
/// character, with each segment at least 10 chars.
fn find_jwt(text: &str) -> Option<&str> {
    let bytes = text.as_bytes();
    let mut i = 0;
    while i + 4 < bytes.len() {
        if bytes[i..].starts_with(b"eyJ") {
            // Find the end of this JWT (whitespace or string end).
            let end = bytes[i..]
                .iter()
                .position(|&b| b == b' ' || b == b'\n' || b == b'\r' || b == b'\t')
                .map(|p| i + p)
                .unwrap_or(bytes.len());
            let candidate = &text[i..end];
            // Must have at least 2 dots and 3 eyJ-prefixed segments.
            let dots = candidate.as_bytes().iter().filter(|&&b| b == b'.').count();
            if dots >= 2 {
                let parts: Vec<&str> = candidate.splitn(3, '.').collect();
                if parts.len() == 3
                    && parts[0].starts_with("eyJ")
                    && parts[1].starts_with("eyJ")
                    && parts[0].len() >= 10
                    && parts[1].len() >= 10
                {
                    return Some(candidate);
                }
            }
            i = end + 1;
        } else {
            i += 1;
        }
    }
    None
}

/// Detect `scheme://user:pass@host` patterns where the `user:pass` portion
/// contains actual credentials (both user and pass non-empty).
fn find_url_userinfo(text: &str) -> Option<&str> {
    let mut search = text;
    let mut base = 0usize;
    while let Some(at_rel) = search.find("://") {
        let at_abs = base + at_rel;
        // After `://`, look for `@` before the next `/`, `?`, ` `, or newline.
        let rest_start = at_abs + 3;
        let rest = &text[rest_start..];
        if let Some(at_pos) = rest.find('@') {
            let userinfo = &rest[..at_pos];
            // Must contain a colon and both sides non-empty.
            if let Some(colon) = userinfo.find(':') {
                let user = &userinfo[..colon];
                let pass = &userinfo[colon + 1..];
                if !user.is_empty() && !pass.is_empty() && pass.len() >= 4 {
                    // Return a slice starting from the scheme.  Walk back from
                    // `at_abs` to the first non-scheme char and resume just past
                    // it.  Use `char_indices` and skip by the separator's full
                    // UTF-8 width: a multibyte separator (e.g. CJK prose before a
                    // credential URL) would otherwise leave `scheme_start` inside
                    // the codepoint and panic the slice below.
                    let scheme_start = text[..at_abs]
                        .char_indices()
                        .rev()
                        .find(|(_, c)| {
                            !c.is_ascii_alphanumeric() && *c != '+' && *c != '-' && *c != '.'
                        })
                        .map(|(idx, c)| idx + c.len_utf8())
                        .unwrap_or(0);
                    // Ensure there are no spaces in userinfo (not a code snippet).
                    if !userinfo.contains(' ') && !userinfo.contains('\n') {
                        let end = rest_start
                            + at_pos
                            + 1
                            + rest[at_pos + 1..]
                                .find([' ', '\n', '\r'])
                                .unwrap_or(rest[at_pos + 1..].len());
                        return Some(&text[scheme_start..end.min(text.len())]);
                    }
                }
            }
        }
        base = at_abs + 3;
        search = &text[base..];
    }
    None
}

// ─── Layer 2: entropy heuristic ─────────────────────────────────────────────

/// Trigger words checked as a bounded standalone word (see
/// [`contains_bounded_word`]) — bare English words that can otherwise appear
/// as a pure substring collision inside unrelated identifiers or prose:
/// `auth` inside `authorized`/`authentication`, `key` inside
/// `monkey`/`turkey`/`keyword`, `secret` inside `secretary`.  Round-5 decision
/// (see the module doc): a substring collision like this poisons the trigger
/// window on prose that never mentions credentials at all, which is a
/// distinct failure mode from a genuine (if topical) mention of the word —
/// see issues #577 / #632.  Matching these words at a word boundary removes
/// the substring-collision false positives while changing nothing about
/// detection of a genuine standalone mention: `auth` as its own word (`auth
/// header`, `auth:`) still triggers exactly as before.
///
/// The bare substring `token` is NOT in this list because it fires on benign
/// terms like `tokenizer`, `token_count`, and `next_token`.  Instead we use
/// the dedicated boundary-aware helpers `has_standalone_token` (standalone word)
/// and `has_token_assignment` (`token=` / `token:` with word boundary before).
const TRIGGER_WORDS: &[&str] = &[
    "key",
    "secret",
    "password",
    "passwd",
    "credential",
    "bearer",
    "auth",
    "apikey",
];

/// Trigger words checked as a plain substring (unchanged behavior) rather than
/// a bounded word — these already embed the underscore separator that
/// disambiguates them from ordinary prose (`secret_access_key`, `api_key`),
/// so word-boundary matching would only weaken detection: an attacker who
/// glues the compound onto a longer identifier (`secret_access_key_v2`) or
/// composes it inside another compound (`aws_secret_access_key`) must still
/// trip the gate. Do not move an entry here unless it structurally requires
/// an underscore to make sense as a trigger.
const COMPOUND_TRIGGER_WORDS: &[&str] = &["api_key", "access_key", "private_key"];

/// Minimum token length to apply the entropy check.
const MIN_ENTROPY_LEN: usize = 24;

/// Shannon entropy threshold (bits per character) above which a token is
/// considered high-entropy.  7.0 corresponds to ~99% utilisation of a
/// 128-symbol alphabet — typical for random base64/hex.
const ENTROPY_THRESHOLD: f64 = 4.5;

/// Window around a trigger word in which a high-entropy token must appear.
const TRIGGER_WINDOW: usize = 120;

/// Largest index `<= i` that lies on a UTF-8 char boundary of `s`. Stable
/// replacement for the unstable `str::floor_char_boundary`; used to snap
/// byte-offset windows that may land inside a multibyte char before slicing.
fn floor_char_boundary(s: &str, i: usize) -> usize {
    let mut i = i.min(s.len());
    while i > 0 && !s.is_char_boundary(i) {
        i -= 1;
    }
    i
}

/// `from` restricts which tokens may be RETURNED (only those starting at or
/// after `from`), but the trigger-context window is still computed over the full
/// `text`. This lets [`mask_secrets`] advance past an earlier redaction without
/// losing a trigger word that sat to the left of it.
fn check_entropy_heuristic(text: &str, from: usize) -> Option<(&str, &'static str)> {
    // Tokenize into maximal ASCII non-whitespace runs, recording each run's byte
    // offset.  Non-ASCII characters are delimiters (alongside ASCII whitespace):
    // real base64/hex/base64url credentials are ASCII, so splitting on non-ASCII
    // isolates an ASCII credential glued to CJK text/punctuation/fullwidth
    // whitespace, while a run of natural-language CJK yields no ASCII run long
    // enough to trip the length floor below.  On pure-ASCII input this is
    // identical to `split_ascii_whitespace`.
    let tokens: Vec<(usize, &str)> = text
        .split(|c: char| c.is_ascii_whitespace() || !c.is_ascii())
        .filter(|t| !t.is_empty())
        .map(|t| {
            let offset = t.as_ptr() as usize - text.as_ptr() as usize;
            (offset, t)
        })
        .collect();

    for &(tok_offset, raw_token) in &tokens {
        // Strip common delimiters that wrap the actual value.
        let token = strip_delimiters(raw_token);
        // Only RETURN tokens at or after `from` (already-redacted spans lie
        // before it); the trigger window below still spans the full text.
        let token_offset = token.as_ptr() as usize - text.as_ptr() as usize;
        if token_offset < from {
            continue;
        }
        if token.len() < MIN_ENTROPY_LEN {
            continue;
        }

        // `token` is ASCII here (non-ASCII was split out at tokenization), so
        // `shannon_entropy` over its bytes is a true per-character entropy.

        // Compute the trigger window BEFORE any shape-based allowlist decision.
        // Every allowlist below (UUID, base64 content-hash, pure-hex) is a
        // prose-context exemption, not an unconditional one: a credential
        // trigger word dominates shape allowlists, because attacker-suppliable
        // shapes (a UUID, a sha-prefixed hash) are exactly as ambiguous near a
        // trigger word as any other high-entropy candidate.
        let window_start = floor_char_boundary(text, tok_offset.saturating_sub(TRIGGER_WINDOW));
        let window_end = floor_char_boundary(text, tok_offset + raw_token.len() + TRIGGER_WINDOW);
        let window = &text[window_start..window_end];
        let low_window = window.to_ascii_lowercase();

        let near_trigger = COMPOUND_TRIGGER_WORDS
            .iter()
            .any(|tw| low_window.contains(tw))
            || TRIGGER_WORDS
                .iter()
                .any(|tw| contains_bounded_word(&low_window, tw))
            || has_standalone_token(&low_window)
            || has_token_assignment(&low_window);

        // UUID canonical form and sha-prefixed base64 content hashes (SRI /
        // npm lockfile integrity) are allowlisted only outside trigger
        // context. Near a trigger, both shapes fall through to detection
        // below instead of being silently passed.
        //
        // A UUID's own character entropy cannot be relied on to catch it once
        // it falls through: hex digits cap at log2(16) = 4.0 bits/char, which
        // never reaches ENTROPY_THRESHOLD (4.5) regardless of token length.
        // The explicit checks immediately below are what actually block a
        // UUID-shaped or hash-shaped token in trigger context; letting it run
        // into the generic entropy computation at the bottom of this loop
        // would silently readmit it. A corpus replay of ~19k real notes/docs
        // measured exactly one benign token (an internal task `area_id` UUID
        // co-occurring with the word "auth" inside `authorized_write`) newly
        // blocked by this rule — an accepted false positive, not a systemic
        // regression.
        //
        // Both exact-shape checkers require the WHOLE token to match, so a
        // credential glued to ordinary storage syntax (`api_key=<uuid>`,
        // `(<uuid>)`, `{"api_key":"<uuid>"}`, a trailing sentence period,
        // a doubled assignment, or a label itself containing `:`/`=`)
        // would otherwise never reach them: `strip_delimiters` above only
        // trims `"'`:=,;` at the token's OUTER ends, not braces/parens, and
        // not an internal `=`/`:` from an assignment form. `value_candidates`
        // enumerates every plausible value extraction from those glued forms
        // specifically for this pair of checks — it does not replace `token`
        // for any other check in this loop (entropy, hex, structured-
        // identifier), none of which require an exact shape match. This is a
        // small bounded iteration over separator positions in one token, not
        // an allocation-heavy scan.
        if near_trigger && value_candidates(token).any(is_uuid_canonical) {
            return Some((token, "uuid-near-trigger"));
        }
        if near_trigger && value_candidates(token).any(is_base64_content_hash) {
            return Some((token, "content-hash-near-trigger"));
        }
        if !near_trigger && (is_uuid_canonical(token) || is_base64_content_hash(token)) {
            continue;
        }

        // Pure hex tokens (git SHA, checksum digests) are allowlisted only when
        // they are NOT near a credential trigger.
        if !near_trigger && is_pure_hex(token) {
            continue;
        }

        // Hex API keys (AWS secret access key, Stripe test keys, random hex
        // tokens) are pure hex yet are real credentials.  The entropy heuristic
        // cannot catch them — hex alphabet maxes at log2(16) = 4.0 bits/char,
        // which is always below ENTROPY_THRESHOLD (4.5).  A credential-shaped
        // hex token (32 / 40 / 64 / 128 chars) near a trigger word is always
        // flagged.  Credential triggers dominate: adding "sha" or "hash" to
        // the window does not rescue the token — a caller controlling the prose
        // could trivially bypass the gate with one extra word.  Safe git SHAs
        // and content-hash digests do not appear near credential trigger words
        // and are already allowed via the `!near_trigger && is_pure_hex` path.
        const HEX_CREDENTIAL_LENGTHS: &[usize] = &[32, 40, 64, 128];
        if near_trigger && is_pure_hex(token) && HEX_CREDENTIAL_LENGTHS.contains(&token.len()) {
            return Some((token, "hex-credential-token"));
        }

        // Structured identifiers (file paths, branch names, ADR/doc slugs,
        // snake_case identifiers) are exempted from the entropy check — see
        // the module doc and `is_structured_identifier`. Must come after the
        // UUID/content-hash and hex-credential-token checks above (neither of
        // which it weakens) and before the entropy computation, since a
        // legitimate path can exceed ENTROPY_THRESHOLD on Shannon entropy
        // alone. The exemption applies ONLY outside trigger context: see the
        // module doc for why no shape-based signal can be made sound near a
        // trigger word; in trigger context this falls through to the entropy
        // heuristic below unconditionally, an accepted false-positive
        // tradeoff for genuine paths that happen to score high entropy.
        if !near_trigger && is_structured_identifier(token) {
            continue;
        }

        let entropy = shannon_entropy(token.as_bytes());
        if entropy < ENTROPY_THRESHOLD {
            continue;
        }

        // High-entropy token in trigger context — flag it.
        if near_trigger {
            return Some((token, "high-entropy-token"));
        }
    }
    None
}

/// Returns `true` when `low_window` contains `needle` as a standalone word —
/// bounded on both sides by a character outside the caller-supplied word-char
/// set (or start/end of string) — rather than merely as a substring.
///
/// `underscore_is_word_char` selects which of two, deliberately different,
/// boundary rules the caller needs:
/// - `true` (used by [`has_standalone_token`] / [`has_token_assignment`] for
///   `token`): underscore is a continuation of the same identifier, so
///   `next_token`, `tokenizer`, and `token_count` do NOT match — a prior,
///   deliberate decision that must not change.
/// - `false` (used by [`contains_bounded_word`] for the bare `TRIGGER_WORDS`):
///   underscore IS a boundary, so `secret_key=`/`auth_token=`/`signing_key=`
///   still match on the `secret`/`auth`/`key` half of the compound — these
///   underscore-joined credential-config compounds (Django/Flask `SECRET_KEY`,
///   OAuth `auth_token`, JWT `signing_key`) are exactly the shape a credential
///   trigger must not lose. Only *letter*-joined collisions (`authorized`,
///   `authentication`, `monkey`, `keyword`) are meant to stop matching.
///
/// CJK/accented prose always counts as a boundary in both modes (only ASCII
/// alphanumerics — plus underscore when `underscore_is_word_char` is `true`
/// — are treated as word characters).
fn contains_word(low_window: &str, needle: &str, underscore_is_word_char: bool) -> bool {
    let is_word_char = |c: char| c.is_ascii_alphanumeric() || (underscore_is_word_char && c == '_');
    let mut start = 0;
    while let Some(rel) = low_window[start..].find(needle) {
        let abs = start + rel;
        let before_ok = abs == 0
            || low_window[..abs]
                .chars()
                .next_back()
                .is_none_or(|c| !is_word_char(c));
        let after_end = abs + needle.len();
        let after_ok = after_end >= low_window.len()
            || low_window[after_end..]
                .chars()
                .next()
                .is_none_or(|c| !is_word_char(c));
        if before_ok && after_ok {
            return true;
        }
        start = abs + needle.len().max(1);
    }
    false
}

/// Returns `true` when `low_window` contains the bare trigger word `needle`
/// as a standalone word, with underscore treated as a BOUNDARY (see
/// [`contains_word`]) — so `secret_key=…`/`auth_token=…`/`signing_key=…`
/// still match (on the `secret`/`auth`/`key` half), while pure letter-joined
/// collisions like `authorized`/`authentication`/`monkey`/`keyword` do not.
fn contains_bounded_word(low_window: &str, needle: &str) -> bool {
    contains_word(low_window, needle, false)
}

/// Returns `true` when `low_window` contains the word `token` as a standalone
/// word, with underscore treated as a WORD CHARACTER / continuation (see
/// [`contains_word`]) — but NOT as part of compound identifiers such as
/// `tokenizer`, `token_count`, or `next_token`. This underscore-as-
/// continuation rule is deliberately different from
/// [`contains_bounded_word`]: `token` alone is not a
/// credential trigger (it fires on too many benign technical terms), so it
/// needs the narrower, underscore-inclusive standalone-word definition,
/// whereas the bare `TRIGGER_WORDS` need underscore-joined compounds like
/// `secret_key` to still register.
fn has_standalone_token(low_window: &str) -> bool {
    contains_word(low_window, "token", true)
}

/// Returns `true` when `low_window` contains the assignment form `token=` or
/// `token:` where the `token` identifier has a word boundary BEFORE it.
///
/// This is boundary-aware so that compound identifiers like `next_token:` or
/// `pagination_token=` do NOT trigger — only a standalone `token=`/`token:`
/// at the start of a field name does.
///
/// Examples that return `true`:  `token=<value>`, `token: <value>`,
///   `"token": "<value>"` (JSON key-value pairs).
/// Examples that return `false`: `next_token: <value>`,
///   `pagination_token=<value>`, `token_count: <value>`.
fn has_token_assignment(low_window: &str) -> bool {
    let needle = "token";
    let mut start = 0;
    while let Some(rel) = low_window[start..].find(needle) {
        let abs = start + rel;
        // Require a word boundary BEFORE `token`.
        let before_ok = abs == 0
            || low_window[..abs]
                .chars()
                .next_back()
                .is_none_or(|c| !c.is_ascii_alphanumeric() && c != '_');
        let after_end = abs + needle.len();
        // Require `=` or `:` immediately after `token` (possibly with surrounding
        // whitespace or quotes stripped by the time we see the lowercased window).
        let after_char = low_window[after_end..].chars().next();
        let after_is_assign = matches!(after_char, Some('=') | Some(':'));
        if before_ok && after_is_assign {
            return true;
        }
        start = abs + needle.len().max(1);
    }
    false
}

// ─── Allowlist helpers ───────────────────────────────────────────────────────

/// Returns `true` for pure-hex tokens (case-insensitive, optional `0x`/`0X` prefix,
/// 8–128 chars) — git SHAs, checksum digests, uuid-hex without hyphens.
///
/// This helper is used with context: pure-hex tokens near credential trigger words
/// are NOT allowlisted (see `check_entropy_heuristic`).  Only call this function
/// when you have already confirmed no trigger context is nearby.
fn is_pure_hex(token: &str) -> bool {
    let hex_part = token
        .strip_prefix("0x")
        .or(token.strip_prefix("0X"))
        .unwrap_or(token);
    hex_part.len() >= 8 && hex_part.len() <= 128 && hex_part.bytes().all(|b| b.is_ascii_hexdigit())
}

/// Returns `true` for tokens that are unambiguous base64/base64url content
/// hashes with an explicit `sha<N>-` prefix (SRI hash, npm lockfile integrity).
///
/// Criteria:
/// - Token starts with `sha<digits>-` (e.g. `sha256-`, `sha384-`, `sha512-`).
/// - The body after the prefix matches a SHA-family length (43, 64, or 86–88
///   unpadded chars).
/// - Every byte in the body is a standard-base64 or URL-safe-base64 character.
/// - Does NOT start with a known vendor-token prefix (those are credentials
///   regardless of alphabet).
///
/// Bare base64 tokens of those lengths WITHOUT the `sha<N>-` prefix are NOT
/// allowlisted here — a 43-char base64url API token near the word "key" is
/// indistinguishable from a sha256 hash body without the prefix, so we require
/// the explicit prefix to avoid false-negative credential escapes.
fn is_base64_content_hash(token: &str) -> bool {
    // Known vendor prefixes — never allowlist even if they look like base64.
    // Includes bare `sk-` to prevent OpenAI-shaped tokens from being allowlisted.
    const VENDOR_PREFIXES: &[&str] = &[
        "sk-",
        "rk_live_",
        "fm2_",
        "vercel_",
        "xoxb-",
        "xoxa-",
        "xoxp-",
        "xoxr-",
        "xoxs-",
        "ghp_",
        "gho_",
        "ghu_",
        "ghs_",
        "ghr_",
        "github_pat_",
        "AKIA",
        "ASIA",
        "AGE-SECRET-KEY-",
        "FlyV1",
    ];
    if VENDOR_PREFIXES.iter().any(|p| token.starts_with(p)) {
        return false;
    }
    // Require an explicit SRI `sha[0-9]+-` prefix.  Bare base64 at sha-length
    // is NOT allowlisted — it is indistinguishable from a real API token.
    let body = if let Some(rest) = token.strip_prefix("sha") {
        // rest starts with digits followed by '-'
        let dash = rest.find('-').unwrap_or(rest.len());
        let digits = &rest[..dash];
        if !digits.is_empty() && digits.bytes().all(|b| b.is_ascii_digit()) && dash < rest.len() {
            &rest[dash + 1..] // everything after "sha<digits>-"
        } else {
            return false; // no valid sha<N>- prefix → not a known content hash
        }
    } else {
        return false; // no sha prefix → not allowlisted
    };
    // Strip optional padding (at most 2 `=`).
    let stripped = body.trim_end_matches('=');
    let pad_removed = body.len() - stripped.len();
    if pad_removed > 2 {
        return false;
    }
    // Accept only SHA-family content-hash lengths (43, 64, 86–88 chars unpadded).
    let n = stripped.len();
    if n != 43 && n != 64 && !(86..=88).contains(&n) {
        return false;
    }
    // Accept both standard-base64 and URL-safe-base64 alphabets.
    stripped
        .bytes()
        .all(|b| b.is_ascii_alphanumeric() || b == b'+' || b == b'/' || b == b'-' || b == b'_')
}

/// Structural separators that gate entry into [`is_structured_identifier`]
/// (rule 1: the token must contain at least one of these). The actual run
/// decomposition (rule 2) splits on every non-alphanumeric character, not
/// just these four — see the doc comment on `is_structured_identifier`.
const STRUCTURAL_SEPARATORS: [char; 4] = ['/', '-', '_', '.'];

/// Largest length a single path/branch/identifier segment (a "run" between
/// separators) may have and still be considered word-shaped.
const MAX_RUN_LEN: usize = 24;

/// Runs whose letter portion is at or below this length skip the
/// case-transition-density check: density is not a meaningful signal on very
/// short runs (e.g. `R1`, `v2`, `ADR`).
const DENSITY_EXEMPT_LETTER_LEN: usize = 4;

/// Maximum case-transition density (transitions divided by letter_count - 1)
/// a run's letter portion may have and still be considered word-shaped.
const MAX_CASE_TRANSITION_DENSITY: f64 = 0.3;

/// Returns `true` when `token` is shaped like a file path, branch name, or
/// other structured identifier rather than a high-entropy secret.
///
/// A structured identifier decomposes into two or more maximal
/// ASCII-alphanumeric "runs" separated by `/`, `-`, `_`, or `.`, where every
/// run is word-shaped: letters-then-digits (`adr079`, `slices234`, `R1`) or
/// pure digits (`20260701`), at most [`MAX_RUN_LEN`] chars, with a low
/// case-transition density in the letter portion. Random base64/base62
/// secrets glued between separators reliably fail this shape check: their
/// case and digit placement is essentially uniform rather than word-like, so
/// a run either exceeds the length cap or mixes case too densely to pass.
///
/// Outside credential-trigger context this shape check alone is sufficient to
/// exempt a token from the entropy heuristic. In trigger context the caller
/// grants NO exemption at all: see the module doc and the call site in
/// [`check_entropy_heuristic`].
fn is_structured_identifier(token: &str) -> bool {
    if !token.contains(|c: char| STRUCTURAL_SEPARATORS.contains(&c)) {
        return false;
    }
    let runs: Vec<&str> = token
        .split(|c: char| !c.is_ascii_alphanumeric())
        .filter(|r| !r.is_empty())
        .collect();
    runs.len() >= 2 && runs.iter().all(|run| is_word_shaped_run(run))
}

/// A single run (segment between structural separators) is word-shaped when
/// it matches `[A-Za-z]+[0-9]*` or `[0-9]+`, is at most [`MAX_RUN_LEN`] chars,
/// and (for the letters-then-digits form) its letter portion has a low
/// case-transition density.
fn is_word_shaped_run(run: &str) -> bool {
    if run.is_empty() || run.len() > MAX_RUN_LEN {
        return false;
    }
    let bytes = run.as_bytes();
    if bytes.iter().all(|b| b.is_ascii_digit()) {
        return true;
    }
    let letter_end = bytes
        .iter()
        .position(|b| !b.is_ascii_alphabetic())
        .unwrap_or(bytes.len());
    // A run that does not start with a letter, and is not pure digits (ruled
    // out above), mixes digits and letters in a shape other than
    // letters-then-digits — not word-shaped.
    if letter_end == 0 {
        return false;
    }
    // Everything after the leading letters must be digits only (no further
    // letters), else the run is not the `[A-Za-z]+[0-9]*` shape.
    if !bytes[letter_end..].iter().all(|b| b.is_ascii_digit()) {
        return false;
    }
    case_transition_density_ok(&run[..letter_end])
}

/// `true` when the case-transition density of `letters` (an all-ASCII-letter
/// string) is at or below [`MAX_CASE_TRANSITION_DENSITY`]. A transition is an
/// adjacent letter pair where one side is uppercase and the other is not.
/// Runs with few enough letters pass automatically (see
/// [`DENSITY_EXEMPT_LETTER_LEN`]) since density is noisy on short strings.
fn case_transition_density_ok(letters: &str) -> bool {
    let chars: Vec<char> = letters.chars().collect();
    if chars.len() <= DENSITY_EXEMPT_LETTER_LEN {
        return true;
    }
    let transitions = chars
        .windows(2)
        .filter(|w| w[0].is_ascii_uppercase() != w[1].is_ascii_uppercase())
        .count();
    let density = transitions as f64 / (chars.len() - 1) as f64;
    density <= MAX_CASE_TRANSITION_DENSITY
}

/// `xxxxxxxx-xxxx-xxxx-xxxx-xxxxxxxxxxxx`
fn is_uuid_canonical(s: &str) -> bool {
    let b = s.as_bytes();
    if b.len() != 36 {
        return false;
    }
    b[8] == b'-'
        && b[13] == b'-'
        && b[18] == b'-'
        && b[23] == b'-'
        && b[..8].iter().all(|c| c.is_ascii_hexdigit())
        && b[9..13].iter().all(|c| c.is_ascii_hexdigit())
        && b[14..18].iter().all(|c| c.is_ascii_hexdigit())
        && b[19..23].iter().all(|c| c.is_ascii_hexdigit())
        && b[24..].iter().all(|c| c.is_ascii_hexdigit())
}

/// Strip common wrapping characters (`"`, `'`, `` ` ``, `:`, `=`) from both ends.
fn strip_delimiters(s: &str) -> &str {
    s.trim_matches(|c| matches!(c, '"' | '\'' | '`' | ':' | '=' | ',' | ';'))
}

/// Strip `{}()[]"'.,;` from both ends of `s`, repeatedly (JSON nests one
/// wrapper inside another).
fn strip_wrappers(s: &str) -> &str {
    s.trim_matches(|c: char| {
        matches!(
            c,
            '{' | '}' | '(' | ')' | '[' | ']' | '"' | '\'' | '`' | '.' | ',' | ';'
        )
    })
}

fn wrapper_strip_repeated(token: &str) -> &str {
    let mut cur = token;
    loop {
        let next = strip_wrappers(cur);
        if next == cur {
            return cur;
        }
        cur = next;
    }
}

/// Yield every candidate value that an assignment/wrapper-glued whitespace
/// token could contain, so shape allowlists that require an EXACT match
/// (`is_uuid_canonical`, `is_base64_content_hash`) still recognize the
/// credential once it is glued to normal storage syntax: `key=value`,
/// `(value)`, `{"key":"value"}`, `key1=key2=value`, a trailing sentence
/// period, or a label itself containing `:`/`=` (`{"api:key":"value"}`).
/// Used only to derive candidates for the near-trigger UUID/content-hash
/// checks in `check_entropy_heuristic` — it does NOT replace `token` for
/// the entropy, hex, or structured-identifier paths, none of which require
/// an exact shape match and so are unaffected by this extraction.
///
/// Strips wrapper punctuation from both ends first, then yields the
/// wrapper-stripped whole token, plus the wrapper-stripped suffix after
/// EVERY internal `=`/`:` occurrence (skipping empty suffixes). No single
/// separator position can be assumed correct: the true key/value or
/// JSON-label boundary might be the first separator (`secret=sha256-...`),
/// but a base64/base64url value can itself end in `=` padding — for a
/// padded content hash that padding IS the last `=` in the token, so a
/// last-separator split would land on the padding boundary instead. A
/// label can also itself contain `:`/`=` (`{"api:key":"<uuid>"}`) or the
/// assignment can be doubled (`key=label=<uuid>`), so neither "first" nor
/// "last" is a sound single choice. Emitting every suffix and letting the
/// caller test each one is the only choice that is sound in all these
/// shapes: the true value always appears as *some* suffix, and a `=`/`:`
/// that lands inside padding or a label simply yields a non-matching
/// suffix that the caller's shape check harmlessly rejects.
///
/// Byte-scan via `char_indices` over an already-short token (whitespace-
/// delimited, so bounded by realistic line length) — no allocation, since
/// this runs in the hot scan path.
fn value_candidates(token: &str) -> impl Iterator<Item = &str> {
    let cur = wrapper_strip_repeated(token);
    std::iter::once(cur).chain(cur.char_indices().filter_map(move |(i, c)| {
        if c == '=' || c == ':' {
            let after = strip_wrappers(&cur[i + c.len_utf8()..]);
            if !after.is_empty() {
                return Some(after);
            }
        }
        None
    }))
}

// ─── Utilities ───────────────────────────────────────────────────────────────

/// Extract a contiguous token (non-whitespace chars) starting at the beginning of `s`.
fn extract_token(s: &str) -> &str {
    let end = s
        .find(|c: char| c.is_whitespace() || c == '\n' || c == '\r')
        .unwrap_or(s.len());
    &s[..end]
}

/// Shannon entropy in bits per character.
///
/// H = -∑ p_i log2(p_i)
fn shannon_entropy(bytes: &[u8]) -> f64 {
    if bytes.is_empty() {
        return 0.0;
    }
    let mut counts = [0u32; 256];
    for &b in bytes {
        counts[b as usize] += 1;
    }
    let len = bytes.len() as f64;
    counts
        .iter()
        .filter(|&&c| c > 0)
        .map(|&c| {
            let p = c as f64 / len;
            -p * p.log2()
        })
        .sum()
}

/// Build a `SecretMatch` from a detector name and the candidate string.
///
/// The masked excerpt is: first 6 chars + "..." + total length.
/// Never includes more than 6 chars of the actual value.
fn build_match(detector: &'static str, candidate: &str) -> SecretMatch {
    let chars: Vec<char> = candidate.chars().collect();
    let preview: String = chars.iter().take(6).collect();
    let masked = format!("{}...{}chars", preview, chars.len());
    SecretMatch { detector, masked }
}

// ─── Tests ───────────────────────────────────────────────────────────────────

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

    #[test]
    fn blocks_aws_akia() {
        // FAKE key: prefix is real shape, 16-char suffix invented.
        let fake = "AKIAFAKEKEY1234567890";
        assert!(scan(fake).is_some(), "AKIA must be caught");
        let m = scan(fake).unwrap();
        assert_eq!(m.detector, "aws-access-key-id");
        // Masked excerpt must not echo the full key.
        assert!(
            !m.masked.contains("FAKEKEY1234567890"),
            "must not echo the secret: {}",
            m.masked
        );
    }

    #[test]
    fn blocks_aws_asia() {
        let fake = "ASIAFAKEKEY00000000000";
        let m = scan(fake);
        assert!(m.is_some(), "ASIA must be caught");
        assert_eq!(m.unwrap().detector, "aws-access-key-id");
    }

    #[test]
    fn blocks_github_ghp() {
        // 36 chars total to pass min_len.
        let fake = "ghp_AAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAA";
        assert!(scan(fake).is_some(), "ghp_ must be caught");
    }

    #[test]
    fn blocks_github_gho() {
        let fake = "gho_BBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBB";
        assert!(scan(fake).is_some(), "gho_ must be caught");
    }

    #[test]
    fn blocks_github_pat() {
        let fake = "github_pat_AAAAAABBBBBBCCCCCC";
        assert!(scan(fake).is_some(), "github_pat_ must be caught");
    }

    #[test]
    fn blocks_openai_sk() {
        let fake = "sk-aaaaaabbbbbbccccccddddddeeeeeeffffgg";
        assert!(scan(fake).is_some(), "sk- must be caught");
    }

    #[test]
    fn blocks_anthropic_sk_ant() {
        let fake = "sk-ant-api03-AAAAAAAAAAAAAAA";
        assert!(scan(fake).is_some(), "sk-ant- must be caught");
        assert_eq!(scan(fake).unwrap().detector, "anthropic-api-key");
    }

    #[test]
    fn blocks_stripe_live() {
        let fake = "sk_live_FAKESTRIPE0000000000000"; // gitleaks:allow
        assert!(scan(fake).is_some(), "sk_live_ must be caught");
        assert_eq!(scan(fake).unwrap().detector, "stripe-secret-key");
    }

    #[test]
    fn blocks_stripe_restricted() {
        let fake = "rk_live_FAKESTRIPE0000000000000"; // gitleaks:allow
        assert!(scan(fake).is_some(), "rk_live_ must be caught");
        assert_eq!(scan(fake).unwrap().detector, "stripe-restricted-key");
    }

    #[test]
    fn blocks_fly_flyv1() {
        let fake = "FlyV1 FAKEFLYTOKEN000000000000000000";
        assert!(scan(fake).is_some(), "FlyV1 must be caught");
        assert_eq!(scan(fake).unwrap().detector, "fly-token");
    }

    #[test]
    fn blocks_fly_fm2() {
        let fake = "fm2_FAKEFLYTOKEN00000000000000000";
        assert!(scan(fake).is_some(), "fm2_ must be caught");
        assert_eq!(scan(fake).unwrap().detector, "fly-token");
    }

    #[test]
    fn blocks_vercel_token() {
        let fake = "vercel_FAKETOKEN00000000000000000";
        assert!(scan(fake).is_some(), "vercel_ must be caught");
        assert_eq!(scan(fake).unwrap().detector, "vercel-token");
    }

    #[test]
    fn blocks_slack_xoxb() {
        let fake = "xoxb-FAKE-SLACKTOKEN-000000000000000000000000";
        assert!(scan(fake).is_some(), "xoxb- must be caught");
        assert_eq!(scan(fake).unwrap().detector, "slack-token");
    }

    #[test]
    fn blocks_pem_private_key() {
        // Split the header so the literal detector-trigger string is not present
        // verbatim in source — pre-commit's detect-private-key hook would fire.
        // The gate detects it at runtime because scan() sees the assembled string.
        let header = ["-----BEGIN RSA", " PRIVATE KEY-----"].concat(); // gitleaks:allow
        let fake = format!("{}\nMIIEo\u{2026}\n-----END RSA PRIVATE KEY-----", header);
        assert!(scan(&fake).is_some(), "PEM private key must be caught");
        assert_eq!(scan(&fake).unwrap().detector, "pem-private-key");
    }

    #[test]
    fn blocks_pem_ec_private_key() {
        let header = ["-----BEGIN EC", " PRIVATE KEY-----"].concat(); // gitleaks:allow
        let fake = format!("{}\nMHQCAQEE\u{2026}\n-----END EC PRIVATE KEY-----", header);
        assert!(scan(&fake).is_some(), "EC PEM must be caught");
    }

    #[test]
    fn blocks_age_secret_key() {
        // AGE-SECRET-KEY- followed by 59 base32 chars (Bech32m body).
        let fake = "AGE-SECRET-KEY-1QQQQQQQQQQQQQQQQQQQQQQQQQQQQQQQQQQQQQQQQQQQQQQQQQQQQQQQQ";
        assert!(scan(fake).is_some(), "AGE-SECRET-KEY- must be caught");
        assert_eq!(scan(fake).unwrap().detector, "age-secret-key");
    }

    #[test]
    fn blocks_jwt_triple() {
        // Synthetic JWT structure: header.payload.signature (no real key).
        let fake = "eyJhbGciOiJIUzI1NiIsInR5cCI6IkpXVCJ9.eyJzdWIiOiIxMjM0NTY3ODkwIn0.FAKE_SIG_XXXXXXXXXXXX"; // gitleaks:allow
        assert!(scan(fake).is_some(), "JWT triple must be caught");
        assert_eq!(scan(fake).unwrap().detector, "jwt");
    }

    #[test]
    fn blocks_url_userinfo() {
        let fake = "postgresql://dbuser:S3cr3tP4ss@db.example.com:5432/mydb";
        assert!(scan(fake).is_some(), "URL userinfo must be caught");
        assert_eq!(scan(fake).unwrap().detector, "url-userinfo");
    }

    #[test]
    fn blocks_high_entropy_near_bearer_word() {
        // 32 random-looking base64 chars adjacent to the word "bearer".
        let fake = "Bearer token: Xk9mZ2vQpLrT8nJwYuAeHfBsDcGiONvM"; // gitleaks:allow
        assert!(
            scan(fake).is_some(),
            "high-entropy value near 'bearer' must be caught"
        );
        assert_eq!(scan(fake).unwrap().detector, "high-entropy-token");
    }

    #[test]
    fn blocks_high_entropy_near_secret_word() {
        let fake = "secret=Xk9mZ2vQpLrT8nJwYuAeHfBsDcGiONvM"; // gitleaks:allow
        assert!(
            scan(fake).is_some(),
            "high-entropy value near 'secret' must be caught"
        );
    }

    #[test]
    fn error_message_masks_secret() {
        let fake = "ghp_AAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAA";
        let m = scan(fake).unwrap();
        // Masked form: first 6 chars + "...N chars".
        // Must NOT contain the full suffix.
        let masked = &m.masked;
        assert!(
            !masked.contains("AAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAA"),
            "mask must not echo the full secret value; got: {masked}"
        );
        // Must start with "ghp_AA" (first 6 chars of the token).
        assert!(
            masked.starts_with("ghp_AA"),
            "mask must show first 6 chars; got: {masked}"
        );
    }

    // ── False-positive suite ─────────────────────────────────────────────────

    #[test]
    fn allows_sha256_hex() {
        // 64-char lowercase hex — typical sha256 digest.
        let sha = "e3b0c44298fc1c149afbf4c8996fb92427ae41e4649b934ca495991b7852b855";
        assert!(
            scan(sha).is_none(),
            "sha256 hex must pass (allowlisted); fired: {:?}",
            scan(sha)
        );
    }

    #[test]
    fn allows_uuid() {
        let uuid = "550e8400-e29b-41d4-a716-446655440000";
        assert!(
            scan(uuid).is_none(),
            "UUID must pass; fired: {:?}",
            scan(uuid)
        );
    }

    #[test]
    fn allows_git_sha() {
        // 40-char lowercase git SHA.
        let sha = "d362950a3c9b1a4cb47d97f1623e38f1a1e6bcdf";
        assert!(
            scan(sha).is_none(),
            "git SHA must pass; fired: {:?}",
            scan(sha)
        );
    }

    #[test]
    fn allows_normal_prose() {
        let prose =
            "The FlashAttention paper introduces IO-aware tiling for transformer self-attention.";
        assert!(scan(prose).is_none(), "normal prose must pass");
    }

    #[test]
    fn allows_code_snippet() {
        let code = r#"fn create_entity(name: &str, kind: &str) -> RuntimeResult<Entity> {
    self.validate_entity_kind(kind)?;
    Ok(Entity::new("local", kind, name))
}"#;
        assert!(
            scan(code).is_none(),
            "code snippet must pass; fired: {:?}",
            scan(code)
        );
    }

    #[test]
    fn allows_long_url_without_credentials() {
        let url = "https://docs.example.com/api/v2/entities?kind=concept&limit=100";
        assert!(scan(url).is_none(), "URL without userinfo must pass");
    }

    #[test]
    fn allows_base64_image_stub() {
        // Realistic short base64 data URI stub — no trigger words, below threshold length.
        let b64 = "data:image/png;base64,iVBORw0KGgoAAAANSUhEUgAAAAEAAAABCAYAAAAfFcSJAAAAC0lEQVQI12NgAAIABQ";
        assert!(
            scan(b64).is_none(),
            "base64 image stub without trigger word must pass; fired: {:?}",
            scan(b64)
        );
    }

    #[test]
    fn allows_long_plain_url() {
        let url = "https://api.github.com/repos/ohdearquant/khive/pulls/76/comments?per_page=100";
        assert!(
            scan(url).is_none(),
            "plain URL must pass; fired: {:?}",
            scan(url)
        );
    }

    #[test]
    fn allows_manifest_content_hash() {
        // A string like what appears in Cargo.lock or npm lockfiles.
        let line =
            "checksum = \"e3b0c44298fc1c149afbf4c8996fb92427ae41e4649b934ca495991b7852b855\"";
        assert!(
            scan(line).is_none(),
            "manifest content hash line must pass; fired: {:?}",
            scan(line)
        );
    }

    #[test]
    fn masked_excerpt_format() {
        let fake = "AKIAFAKEKEY1234567890";
        let m = scan(fake).unwrap();
        // Format: first6...Nchars
        assert!(m.masked.contains("..."), "masked must contain '...'");
        assert!(m.masked.ends_with("chars"), "masked must end with 'chars'");
    }

    // ── Gate function ────────────────────────────────────────────────────────

    #[test]
    fn check_returns_ok_for_safe_content() {
        assert!(check("A normal memory note about LoRA.").is_ok());
    }

    #[test]
    fn check_returns_err_for_secret() {
        let fake = "AKIAFAKEKEY1234567890";
        let result = check(fake);
        assert!(result.is_err(), "check must fail for AKIA key");
        let err = result.unwrap_err();
        assert!(
            matches!(err, RuntimeError::SecretDetected(_)),
            "error variant must be SecretDetected"
        );
    }

    // ── Entropy helpers ──────────────────────────────────────────────────────

    #[test]
    fn entropy_of_uniform_string_is_zero() {
        let s = "aaaaaaaaaaaaaaaa";
        assert!(shannon_entropy(s.as_bytes()) < 0.01);
    }

    #[test]
    fn entropy_of_random_bytes_is_high() {
        // A truly random-looking string should exceed 4.5 bits/char.
        let s = b"X9kZ2vQpLrT8nJwYuAeHfBsDcGiONvM1"; // 32 mixed base64 chars
        assert!(shannon_entropy(s) > 4.5, "entropy={}", shannon_entropy(s));
    }

    #[test]
    fn cjk_prose_near_trigger_is_not_flagged() {
        // Regression: a multibyte CJK run (~19 chars = 57 bytes) clears the
        // byte-length floor, and `shannon_entropy` over UTF-8 bytes reads it as
        // high-entropy — so a Chinese title near the `auth` trigger word used to
        // false-positive as `high-entropy-token`.  Non-ASCII tokens are now
        // skipped by the entropy heuristic: real base64/hex credentials are
        // ASCII, so this cannot hide a secret.
        let content = "更新 auth 配置数据库连接管理系统核心模块设计文档";
        assert!(
            check(content).is_ok(),
            "CJK prose near a trigger word must not be flagged as a secret"
        );
    }

    #[test]
    fn ascii_secret_near_trigger_still_flagged() {
        // The non-ASCII skip must NOT weaken detection of genuine ASCII
        // high-entropy credentials near a trigger word.
        let content = "api_key X9kZ2vQpLrT8nJwYuAeHfBsDcGiONvM1";
        assert!(
            check(content).is_err(),
            "ASCII high-entropy token near a trigger word must still be blocked"
        );
    }

    #[test]
    fn ascii_secret_in_cjk_context_does_not_panic_and_is_flagged() {
        // The ±120-byte trigger window around an ASCII token can land in the
        // middle of a multibyte CJK character when the token is embedded in
        // non-Latin prose.  Slicing on a non-char-boundary would panic — the
        // window bounds are snapped via `floor_char_boundary`.  Detection of
        // the genuine ASCII secret must still fire.
        let cjk = "数据库连接管理系统核心模块设计文档".repeat(6); // 17 chars × 6 = 306 bytes
                                                                  // The leading single-byte `x` breaks 3-byte CJK alignment so the window
                                                                  // start (token_offset - 120) lands mid-character without the snap.
        let content = format!("{cjk}x api_key X9kZ2vQpLrT8nJwYuAeHfBsDcGiONvM1 {cjk}");
        assert!(
            check(&content).is_err(),
            "ASCII secret in CJK context must still be blocked (and must not panic)"
        );
    }

    #[test]
    fn ascii_secret_glued_to_cjk_is_still_flagged() {
        // Regression: a prefixless high-entropy credential glued (no ASCII
        // whitespace) to CJK text, CJK brackets/quotes, a fullwidth space, or a
        // fullwidth colon used to slip through, because the whole whitespace token
        // contained a non-ASCII byte and was skipped wholesale.  Non-ASCII is now
        // a token delimiter, so the ASCII credential run is isolated and
        // entropy-checked while the surrounding ±120-byte window still sees the
        // trigger word.
        let secret = "X9kZ2vQpLrT8nJwYuAeHfBsDcGiONvM1"; // gitleaks:allow
        let cases = [
            format!("api_key {secret}数据"),     // CJK suffix glued to the token
            format!("api_key 「{secret}」"),     // CJK brackets wrap the token
            format!("api_key　{secret}"),        // U+3000 ideographic space separator
            format!("api_key：{secret}"),        // U+FF1A fullwidth colon separator
            format!("数据{secret}更新 api_key"), // CJK-glued prefix, trigger after
        ];
        for content in &cases {
            assert!(
                check(content).is_err(),
                "ASCII secret glued to CJK must be blocked: {content:?}"
            );
        }
    }

    #[test]
    fn high_entropy_ascii_run_without_trigger_is_not_flagged() {
        // The non-ASCII-as-delimiter change must not weaken the trigger-context
        // discipline: a high-entropy ASCII run isolated from CJK prose but NOT
        // near a credential trigger word is still allowed (only the tokenizer
        // changed, not the `near_trigger` gate).
        let secret = "X9kZ2vQpLrT8nJwYuAeHfBsDcGiONvM1"; // gitleaks:allow
        let content = format!("数据库连接{secret}核心模块设计文档");
        assert!(
            check(&content).is_ok(),
            "high-entropy ASCII run with no trigger word must not be flagged"
        );
    }

    #[test]
    fn known_prefix_secret_glued_after_cjk_is_still_flagged() {
        // A Layer-1 known-prefix secret glued directly after
        // CJK prose (no ASCII whitespace) was missed, because the prefix boundary
        // check used `is_alphanumeric` — which Rust counts true for CJK — so the
        // preceding ideograph was not treated as a delimiter.  These credentials
        // must be caught with no nearby ASCII trigger word, on the left side too.
        let cases = [
            "数据AKIAIOSFODNN7EXAMPLE",             // gitleaks:allow
            "令牌github_pat_11ABCDEFG0HIJKLMNOPQR", // gitleaks:allow
            "密钥sk-ant-api03-AAAAAAAAAAAAAAAAAA",  // gitleaks:allow
            "配置FlyV1 fm2_AAAABBBBCCCCDDDD",       // gitleaks:allow
        ];
        for content in cases {
            assert!(
                check(content).is_err(),
                "known-prefix secret glued after CJK must be blocked: {content:?}"
            );
        }
    }

    #[test]
    fn url_userinfo_after_cjk_does_not_panic_and_is_flagged() {
        // A credential URL glued after CJK prose panicked,
        // because scheme_start was (separator byte index + 1) — one byte into a
        // multibyte CJK separator — and the slice fell on a non-char boundary.
        // The public check() API must return a controlled error, never panic.
        let cases = [
            "数据postgresql://dbuser:S3cr3tP4ss@db.example.com/db", // gitleaks:allow
            "配置mysql://root:hunter2pw@10.0.0.1:3306/app",         // gitleaks:allow
            "连接redis://svc:V3ryS3cretPw@cache.internal:6379",     // gitleaks:allow
        ];
        for content in cases {
            assert!(
                check(content).is_err(),
                "credential URL after CJK must be blocked, not panic: {content:?}"
            );
        }
    }

    #[test]
    fn non_ascii_glued_token_trigger_is_still_flagged() {
        // `token=`/`token:`/standalone `token` glued directly
        // after non-ASCII prose was missed because has_standalone_token /
        // has_token_assignment used is_alphanumeric for the word boundary — CJK,
        // accented letters, and fullwidth digits all count as alphanumeric in
        // Rust, so the preceding char was not seen as a boundary and the `token`
        // trigger was suppressed, leaving the high-entropy value unflagged.
        let opaque = "Xk9mZ2vQpLrT8nJwYuAeHfBsDcGiONvMabcdef"; // gitleaks:allow
        let blocked = [
            format!("数据token={opaque}"),    // CJK + assignment form, ASCII '='
            format!("配置token: {opaque}"),   // CJK + assignment form, ASCII ':'
            format!("密钥token {opaque}"),    // CJK + standalone-word form
            format!("résumétoken: {opaque}"), // accented letter before `token`
            format!("１token: {opaque}"),     // fullwidth digit before `token`
        ];
        for content in &blocked {
            assert!(
                check(content).is_err(),
                "non-ASCII-glued token trigger must flag the value: {content:?}"
            );
        }
        // Compound identifiers stay excluded — the `_` boundary rule is unchanged
        // and an ASCII letter before `token` is still a continuation, so these
        // (including the pure-ASCII `servicetoken:`) must still pass.
        let allowed = [
            format!("数据next_token: {opaque}"),
            format!("数据token_count: {opaque}"),
            format!("servicetoken: {opaque}"),
        ];
        for content in &allowed {
            assert!(
                check(content).is_ok(),
                "compound token identifier must not be flagged: {content:?}"
            );
        }
    }

    #[test]
    fn allowlist_passes_sha256() {
        // A plain sha256 hex digest passes via `is_pure_hex` (not `is_allowlisted`
        // because hex is now context-dependent; this tests the primitive directly).
        let sha = "e3b0c44298fc1c149afbf4c8996fb92427ae41e4649b934ca495991b7852b855";
        assert!(is_pure_hex(sha));
    }

    #[test]
    fn allowlist_passes_uuid_canonical() {
        assert!(is_uuid_canonical("550e8400-e29b-41d4-a716-446655440000"));
    }

    #[test]
    fn allowlist_does_not_pass_mixed_token() {
        // A token that starts with letters but mixes in non-hex chars.
        assert!(!is_pure_hex("sk-aaaaaabbbbbbccccccddddddeeeeeeffffgg"));
    }

    // ── Structured-field gate helpers ────────────────────────────────────────

    #[test]
    fn check_json_blocks_secret_in_object_value() {
        let props = serde_json::json!({ "api_key": "AKIAFAKEKEY1234567890" });
        assert!(
            check_json(&props).is_err(),
            "secret in properties object value must be blocked"
        );
    }

    #[test]
    fn check_json_blocks_secret_in_nested_object() {
        let props = serde_json::json!({ "credentials": { "token": "sk-proj-FAKEKEY00000000000000000000000000000000" } }); // gitleaks:allow
        assert!(
            check_json(&props).is_err(),
            "secret in nested properties object must be blocked"
        );
    }

    #[test]
    fn check_json_blocks_secret_in_array() {
        let props = serde_json::json!(["normal", "AKIAFAKEKEY1234567890"]);
        assert!(
            check_json(&props).is_err(),
            "secret in JSON array must be blocked"
        );
    }

    #[test]
    fn check_json_passes_safe_properties() {
        let props = serde_json::json!({
            "domain": "attention",
            "status": "researched",
            "year": 2024
        });
        assert!(
            check_json(&props).is_ok(),
            "normal properties must pass; fired: {:?}",
            check_json(&props).err()
        );
    }

    #[test]
    fn check_tags_blocks_credential_tag() {
        let tags = vec![
            "type:concept".to_string(),
            "AKIAFAKEKEY1234567890".to_string(),
        ];
        assert!(
            check_tags(&tags).is_err(),
            "credential-shaped tag must be blocked"
        );
    }

    #[test]
    fn check_tags_passes_normal_tags() {
        let tags = vec!["type:concept".to_string(), "domain:attention".to_string()];
        assert!(
            check_tags(&tags).is_ok(),
            "normal tags must pass; fired: {:?}",
            check_tags(&tags).err()
        );
    }

    // ── False-positive: sk-learn and scikit-learn slugs ──────────────────────

    #[test]
    fn allows_sk_learn_prose() {
        // scikit-learn slug used as an entity name or knowledge atom.
        let texts = &[
            "sk-learn is a Python machine learning library",
            "sk-learn-compatible transformer pipeline reference",
            "sk-learn scikit-learn estimator interface",
        ];
        for t in texts {
            assert!(
                scan(t).is_none(),
                "sk-learn prose must pass; fired: {:?} on {:?}",
                scan(t),
                t
            );
        }
    }

    #[test]
    fn blocks_openai_sk_proj_not_confused_with_sk_learn() {
        // Real OpenAI key shape must still be caught.
        let fake = "sk-proj-FAKEKEY00000000000000000000000000000000"; // gitleaks:allow
        assert!(
            scan(fake).is_some(),
            "sk-proj- key must still be caught after sk-learn exemption"
        );
    }

    // ── False-positive: SRI / tokenizer hash metadata ────────────────────────

    #[test]
    fn blocks_sri_hash_near_key_word_accepted_fp() {
        // SRI hash as used in HTML integrity attributes (sha384, base64-encoded),
        // placed directly beside the trigger word "key". The content-hash
        // allowlist is a prose-context exemption, not unconditional: near a
        // credential trigger, a sha-prefixed hash falls through to the explicit
        // near-trigger content-hash detector like any other high-entropy
        // candidate. This is an accepted false positive on a real but rare
        // shape (an integrity hash literally next to the word "key").
        let line = "integrity key: sha384-oqVuAfXRKap7fdgcCY5uykM6+R9GqQ8K/uxy9rx7HNQlGYl1kPzQho1wx4JwY8wC";
        assert!(
            scan(line).is_some(),
            "SRI hash near trigger word 'key' must now be blocked (accepted FP); passed unexpectedly"
        );
    }

    #[test]
    fn allows_base64_tokenizer_hash_metadata() {
        // Tokenizer metadata containing a base64 hash near technical keywords.
        let line = "tokenizer_vocab_hash: Xk9mZ2vQpLrT8nJwYuAeHfBsDcGiONvM"; // gitleaks:allow
        assert!(
            scan(line).is_none(),
            "tokenizer hash metadata must pass; fired: {:?}",
            scan(line)
        );
    }

    #[test]
    fn allows_npm_lockfile_integrity() {
        // npm lockfile integrity line with sha512 base64url hash (86 base64 chars + ==).
        // sha512 digest = 64 bytes → base64 = 88 chars (86 unpadded + ==).
        let body_86 = "Xk9mZ2vQpLrT8nJwYuAeHfBsDcGiONvM1234567890abcdefghijklmnopqrstuvwxABCDEFGHIJKLMNOPQRST";
        assert_eq!(body_86.len(), 86, "test body must be exactly 86 chars");
        let line = format!(
            "resolved: https://registry.npmjs.org/foo/-/foo-1.0.0.tgz\nintegrity: sha512-{body_86}=="
        );
        assert!(
            scan(&line).is_none(),
            "npm lockfile integrity must pass; fired: {:?}",
            scan(&line)
        );
    }

    // ── False-positive: tokenizer vs token trigger word ─────────────────────

    #[test]
    fn allows_tokenizer_vocab_hash_no_block() {
        // `tokenizer_vocab_hash` contains the substring "token" but NOT as a
        // standalone word (followed by 'i' which is alphanumeric), so the
        // standalone-token boundary check must not fire here.
        let line = "tokenizer_vocab_hash = Xk9mZ2vQpLrT8nJwYuAeHfBsDcGiONvM"; // gitleaks:allow
        assert!(
            scan(line).is_none(),
            "tokenizer_vocab_hash must pass; 'token' is only standalone-word matched; fired: {:?}",
            scan(line)
        );
    }

    // ── True-positives: bare base64 at sha-lengths near trigger words ────────

    #[test]
    fn blocks_bare_base64url_43chars_near_key() {
        // A 43-char base64url token (= sha256 body length) near the word "key".
        // Without a sha<N>- prefix this MUST be caught, not allowlisted.
        let token_43 = "wJalrXUtnFEMI-K7MDENGbPxRfiCYEXAMPLEKEYX123"; // gitleaks:allow
        assert_eq!(token_43.len(), 43, "test token must be exactly 43 chars");
        let line = format!("api key {token_43}");
        assert!(
            scan(&line).is_some(),
            "43-char base64url token near 'key' must be caught (no sha-prefix = not a hash); fired: {:?}",
            scan(&line)
        );
    }

    #[test]
    fn blocks_bare_base64url_64chars_near_secret() {
        // A 64-char base64url token (= sha384 body length) near "secret".
        // Must be caught without sha<N>- prefix.
        let token_64 = "wJalrXUtnFEMI-K7MDENGbPxRfiCYEXAMPLEKEYX123wJalrXUtnFEMI-K7MDENa"; // gitleaks:allow
        assert_eq!(token_64.len(), 64, "test token must be exactly 64 chars");
        let line = format!("secret: {token_64}");
        assert!(
            scan(&line).is_some(),
            "64-char base64url token near 'secret' must be caught; got: {:?}",
            scan(&line)
        );
    }

    #[test]
    fn blocks_bare_base64url_86chars_near_auth() {
        // An 86-char base64url token (= sha512 body length) near "auth".
        // Must be caught without sha<N>- prefix.
        let token_86 = "wJalrXUtnFEMI-K7MDENGbPxRfiCYEXAMPLEKEYX123wJalrXUtnFEMI-K7MDENwJalrXUtnFEMI-K7MDENabc"; // gitleaks:allow
        assert_eq!(token_86.len(), 86, "test token must be exactly 86 chars");
        let line = format!("auth header {token_86}");
        assert!(
            scan(&line).is_some(),
            "86-char base64url token near 'auth' must be caught; got: {:?}",
            scan(&line)
        );
    }

    // ── True-positives: standalone `token` trigger ───────────────────────────

    #[test]
    fn blocks_service_token_opaque_value() {
        // "service token <opaque-high-entropy>" — `token` as a standalone word
        // with a high-entropy value must be caught.
        let opaque = "Xk9mZ2vQpLrT8nJwYuAeHfBsDcGiONvMabcdef"; // gitleaks:allow
        assert!(
            opaque.len() >= 24,
            "opaque must be long enough for entropy check"
        );
        let line = format!("service token {opaque}");
        assert!(
            scan(&line).is_some(),
            "service token <opaque> must be caught by standalone 'token' check; got: {:?}",
            scan(&line)
        );
    }

    #[test]
    fn blocks_token_equals_credential() {
        // `token=<high-entropy>` (assignment form) must be caught via has_token_assignment.
        let opaque = "Xk9mZ2vQpLrT8nJwYuAeHfBsDcGiONvMabcdef"; // gitleaks:allow
        let line = format!("token={opaque}");
        assert!(
            scan(&line).is_some(),
            "token=<value> must be caught via token= trigger; got: {:?}",
            scan(&line)
        );
    }

    #[test]
    fn blocks_token_colon_credential() {
        // `token: <high-entropy>` (key-value form) must be caught via has_token_assignment.
        let opaque = "Xk9mZ2vQpLrT8nJwYuAeHfBsDcGiONvMabcdef"; // gitleaks:allow
        let line = format!("token: {opaque}");
        assert!(
            scan(&line).is_some(),
            "token: <value> must be caught via token: trigger; got: {:?}",
            scan(&line)
        );
    }

    #[test]
    fn allows_next_token_technical_context() {
        // `next_token` is a technical term; the high-entropy value here has low
        // entropy anyway, so it must pass.
        let line = "next_token: cursor-page-2-abcdef12345678";
        assert!(
            scan(line).is_none(),
            "next_token technical context must not be blocked; fired: {:?}",
            scan(line)
        );
    }

    // ── Boundary-aware token= / token: (compound identifiers must pass) ─────

    #[test]
    fn allows_next_token_high_entropy_cursor() {
        // `next_token:` with a realistic high-entropy pagination cursor must NOT be
        // blocked.  `next_token` has `_token` suffix — not a standalone assignment form.
        let cursor = "Xk9mZ2vQpLrT8nJwYuAeHfBsDcGiONvMabcdef"; // gitleaks:allow
        let line = format!("next_token: {cursor}");
        assert!(
            scan(&line).is_none(),
            "next_token with high-entropy cursor must pass (compound identifier); fired: {:?}",
            scan(&line)
        );
    }

    #[test]
    fn allows_token_count_high_entropy() {
        // `token_count:` with a high-entropy value must NOT be blocked.
        // `token_count` has `token_` prefix — the word boundary after `token` is `_`,
        // which is excluded by has_token_assignment.
        let opaque = "Xk9mZ2vQpLrT8nJwYuAeHfBsDcGiONvMabcdef"; // gitleaks:allow
        let line = format!("token_count: {opaque}");
        assert!(
            scan(&line).is_none(),
            "token_count with high-entropy value must pass; fired: {:?}",
            scan(&line)
        );
    }

    // ── Hex allowlist is not applied when trigger context is present ────────
    //
    // Pure hex strings have a theoretical maximum entropy of log2(16) = 4.0 bits/char,
    // which is below the ENTROPY_THRESHOLD of 4.5.  That means pure hex tokens cannot
    // reach the entropy threshold and will never be flagged by the heuristic alone.
    //
    // However, the hex allowlist was previously applied BEFORE the trigger window was
    // computed, meaning a future threshold reduction or edge case could silently
    // skip credential-context hex.  The fix: compute trigger context first; only
    // apply the hex allowlist when NOT near a trigger.  The tests below verify the
    // structural change is in place by confirming that non-pure-hex high-entropy
    // tokens near triggers are caught (showing the trigger path is live), and that
    // purely hex tokens near triggers still correctly pass (entropy too low to flag).

    #[test]
    fn hex_near_key_blocked_in_credential_context() {
        // A pure-hex 32-char token near "api key" is a credential-shaped hex
        // token in trigger context.  Entropy alone cannot flag it (hex max =
        // 4.0 < 4.5 threshold), but the explicit hex-credential-token path
        // must catch it.
        let hex32 = "4f9c2e8a1d3b5c7e9f0a2b4d6e8c0a2b";
        assert_eq!(hex32.len(), 32);
        let line = format!("api key {hex32}");
        assert!(
            scan(&line).is_some(),
            "32-char pure hex near 'api key' must be blocked; got None"
        );
    }

    #[test]
    fn hex_credential_lengths_blocked_near_trigger() {
        // Verify all four credential-shaped lengths are caught near a trigger.
        let hex40 = "a3f5c2e9d1b8047e63a1f4c2d5b6e8f1a9c3d2e4";
        let hex64 = "1a2b3c4d5e6f7a8b9c0d1e2f3a4b5c6d7e8f9a0b1c2d3e4f5a6b7c8d9e0f1a2b";
        let hex128 = format!("{hex64}{hex64}");
        assert_eq!(hex40.len(), 40);
        assert_eq!(hex64.len(), 64);
        assert_eq!(hex128.len(), 128);

        for (label, hex) in &[
            ("hex40", hex40),
            ("hex64", hex64),
            ("hex128", hex128.as_str()),
        ] {
            let line = format!("secret key: {hex}");
            assert!(
                scan(&line).is_some(),
                "{label} near 'secret key' must be blocked; got None"
            );
        }
    }

    #[test]
    fn hex_blocked_when_trigger_and_hash_word_coexist() {
        // Credential trigger dominates: adding "hash" or "sha" to the window does
        // not rescue a pure-hex token when a credential trigger is also present.
        // An attacker controlling the prose could otherwise bypass the gate with
        // one extra word, so the hash-word exception must NOT apply in trigger context.
        let hex32 = "4f9c2e8a1d3b5c7e9f0a2b4d6e8c0a2b";
        let key_hash_line = format!("api key hash {hex32}");
        let secret_sha_line = format!("secret sha {hex32}");
        assert!(
            scan(&key_hash_line).is_some(),
            "'api key hash <hex32>' must be blocked; got None"
        );
        assert!(
            scan(&secret_sha_line).is_some(),
            "'secret sha <hex32>' must be blocked; got None"
        );
    }

    #[test]
    fn hex_near_sha_context_word_allowed() {
        // A 40-char hex with "sha" or "commit" in the window — but no credential
        // trigger — must be allowed (git SHA or content hash in normal prose).
        let hex40 = "da39a3ee5e6b4b0d3255bfef95601890afd80709";
        let sha_line = format!("sha1: {hex40}");
        let commit_line = format!("commit sha {hex40}");
        assert!(
            scan(&sha_line).is_none(),
            "hex40 near 'sha1' context must be allowed; fired: {:?}",
            scan(&sha_line)
        );
        assert!(
            scan(&commit_line).is_none(),
            "hex40 near 'commit sha' context must be allowed; fired: {:?}",
            scan(&commit_line)
        );
    }

    #[test]
    fn hex64_near_hash_context_allowed() {
        // A 64-char hex near "sha256" or "hash" — with no credential trigger —
        // must be allowed (content digest in normal prose).
        let hex64 = "1a2b3c4d5e6f7a8b9c0d1e2f3a4b5c6d7e8f9a0b1c2d3e4f5a6b7c8d9e0f1a2b";
        let sha_line = format!("sha256: {hex64}");
        let hash_line = format!("hash value {hex64}");
        assert!(
            scan(&sha_line).is_none(),
            "hex64 near 'sha256' must be allowed; fired: {:?}",
            scan(&sha_line)
        );
        assert!(
            scan(&hash_line).is_none(),
            "hex64 near 'hash' must be allowed; fired: {:?}",
            scan(&hash_line)
        );
    }

    #[test]
    fn blocks_high_entropy_hex_like_token_near_key() {
        // A token whose character set exceeds pure hex (contains mixed-case, digits,
        // and non-hex chars) that ALSO passes `is_pure_hex = false` AND has high
        // entropy AND appears near "key" MUST be caught.  This is the realistic
        // real-world case: hex-looking API tokens often mix case and non-hex chars.
        // Example: a 32-char mixed-charset token near "api key".
        let mixed = "Xk9mZ2vQpLrT8nJwYuAeHfBsDcGiONvM"; // gitleaks:allow — not pure hex
        assert!(!is_pure_hex(mixed), "test token must not be pure hex");
        let line = format!("api key {mixed}");
        assert!(
            scan(&line).is_some(),
            "mixed-charset high-entropy token near 'api key' must be caught; got: {:?}",
            scan(&line)
        );
    }

    #[test]
    fn allows_hex40_without_trigger() {
        // 40-char hex string in a neutral context (no trigger word) must still pass —
        // it's likely a git commit SHA or content hash.
        let hex40 = "da39a3ee5e6b4b0d3255bfef95601890afd80709";
        let line = format!("commit: {hex40}");
        assert!(
            scan(&line).is_none(),
            "40-char hex without trigger word must pass; fired: {:?}",
            scan(&line)
        );
    }

    // ── check_json scans object keys ─────────────────────────────────────────

    #[test]
    fn check_json_blocks_secret_in_object_key() {
        // A credential used as a JSON object key (not a value) must be caught.
        let props = serde_json::json!({ "ghp_FakeGitHubToken0000000000000000000": "redacted" }); // gitleaks:allow
        assert!(
            check_json(&props).is_err(),
            "credential as JSON object key must be blocked"
        );
    }

    #[test]
    fn check_json_blocks_nested_secret_key() {
        // Nested credential key must be caught.
        let props = serde_json::json!({
            "metadata": {
                "AKIAFAKEKEY000000000": "value" // gitleaks:allow
            }
        });
        assert!(
            check_json(&props).is_err(),
            "nested credential as JSON object key must be blocked"
        );
    }

    // ── PEM masking format ───────────────────────────────────────────────────

    #[test]
    fn pem_masked_excerpt_reflects_block_length_not_rest_of_string() {
        let header = ["-----BEGIN RSA", " PRIVATE KEY-----"].concat(); // gitleaks:allow
        let fake = format!(
            "{}\nMIIEo\u{2026}\n-----END RSA PRIVATE KEY-----\nsome trailing text that is very long",
            header
        );
        let m = scan(&fake).unwrap();
        assert_eq!(m.detector, "pem-private-key");
        // The masked length should reflect only the key block, not the whole string.
        // "some trailing text that is very long" is ~37 chars; total string is much longer.
        // The block ends after "-----END RSA PRIVATE KEY-----\n".
        // We just verify it is shorter than the full string length.
        let full_len = fake.chars().count();
        let reported_len: usize = m
            .masked
            .trim_end_matches("chars")
            .rsplit("...")
            .next()
            .and_then(|s| s.parse().ok())
            .unwrap_or(full_len + 1);
        assert!(
            reported_len < full_len,
            "masked length ({reported_len}) should be less than full string length ({full_len})"
        );
    }

    // ── UTF-8 char-boundary reproduction tests ───────────────────────────────
    //
    // These tests verify that no code path in secret_gate panics when multibyte
    // UTF-8 characters (emoji, CJK, accented Latin) appear at positions where
    // byte-level slicing could land mid-codepoint.  Each test targets a specific
    // code path.  A panic means the bug is live; a pass means the path is safe.

    /// `build_match` masked preview: if the detected candidate starts with
    /// multibyte chars the "first 6 chars" preview must not slice on a byte
    /// boundary that falls mid-codepoint.  build_match already uses
    /// `chars().take(6)`, but we exercise it with emoji-prefixed candidates.
    #[test]
    fn utf8_build_match_preview_multibyte_prefix_no_panic() {
        // "🔑" = 4 bytes; repeat 3 times = 12 bytes for only 3 chars.
        // A ghp_-prefixed token with an emoji: let's construct a scenario where
        // a known-prefix secret is immediately adjacent to multibyte content so
        // that build_match receives a slice starting at a multibyte char.
        // PEM block with multibyte chars in the body exercises build_match on a
        // candidate that may contain non-ASCII.
        let header = ["-----BEGIN RSA", " PRIVATE KEY-----"].concat(); // gitleaks:allow
        let fake = format!("{}\n🔑密钥\n-----END RSA PRIVATE KEY-----", header);
        // Must not panic; mask must not echo full body.
        let m = scan(&fake);
        assert!(m.is_some(), "PEM with emoji body must still be caught");
        let m = m.unwrap();
        assert!(
            !m.masked.contains("🔑密钥"),
            "mask must not echo the emoji body"
        );
    }

    /// `extract_token` called with a string starting with multibyte chars:
    /// the FlyV1 handler calls `extract_token(&text[payload_start..])` where
    /// `payload_start` is just past "FlyV1 " (ASCII).  If the payload is ASCII
    /// this is trivially safe, but we verify it cannot panic when the rest of
    /// the text after the payload contains multibyte chars.
    #[test]
    fn utf8_extract_token_multibyte_suffix_no_panic() {
        // "FlyV1 ABCDEFGHIJ密钥" — the payload is "ABCDEFGHIJ密钥"; extract_token
        // must stop at the ideographic chars (which are NOT ASCII whitespace) and
        // return the whole glued run without panicking.
        let text = "FlyV1 ABCDEFGHIJ密钥";
        // scan() must not panic.
        let _ = scan(text);
    }

    /// `find_prefix_token` with multibyte chars immediately before and after
    /// the known prefix: checks text[..abs] boundary slices and
    /// extract_token(&text[abs..]) do not panic.
    #[test]
    fn utf8_prefix_detector_multibyte_adjacent_no_panic() {
        // 🔑 (4 bytes) immediately before AKIA: boundary at abs = 4, which is a
        // valid char boundary (end of the emoji).  extract_token sees ASCII from abs.
        let text = "🔑AKIAFAKEKEY00000000000000";
        let _ = scan(text); // must not panic

        // é (U+00E9 = 2 bytes) immediately before ghp_:
        let text2 = "éghp_AAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAA";
        let _ = scan(text2); // must not panic

        // Emoji immediately after the token — extract_token ends at the emoji
        // (non-whitespace, but non-ASCII acts as delimiter in entropy heuristic).
        // For prefix tokens extract_token stops at ASCII whitespace only, so the
        // emoji would be included in the token length measurement.
        let text3 = "AKIAFAKEKEY00000000000000🔑";
        let _ = scan(text3); // must not panic
    }

    /// `find_jwt` with multibyte chars as "whitespace" adjacent to a JWT-like
    /// candidate: `i = end + 1` could skip into a multibyte char if `end`
    /// pointed at a non-ASCII byte.  The position() search only looks for ASCII
    /// whitespace bytes, so a multibyte space (U+3000) is NOT found — `end`
    /// equals bytes.len() and `i = bytes.len() + 1` exits the loop.  Still
    /// verify no panic on CJK-surrounded JWT-like content.
    #[test]
    fn utf8_jwt_multibyte_adjacent_no_panic() {
        // A (fake) JWT-like triple surrounded by CJK text.
        let jwt = "eyJhbGciOiJIUzI1NiIsInR5cCI6IkpXVCJ9.eyJzdWIiOiIxMjM0NTY3ODkwIn0.FAKE_SIG_XXXXXXXXXXXX"; // gitleaks:allow
        let text = format!("数据{jwt}密钥");
        let _ = scan(&text); // must not panic

        // JWT followed by ideographic space (U+3000 = 3 bytes 0xE3 0x80 0x80) —
        // not matched by the ASCII-whitespace position() search.
        let text2 = format!("{jwt}\u{3000}morecontent");
        let _ = scan(&text2); // must not panic

        // JWT followed by emoji
        let text3 = format!("{jwt}🔑");
        let _ = scan(&text3); // must not panic
    }

    /// `find_url_userinfo` with multibyte chars between "://" and "@":
    /// `at_pos` from `rest.find('@')` and `colon` from `userinfo.find(':')` are
    /// ASCII markers (char boundaries), but `scheme_start` calculation uses
    /// char_indices().rev() which must handle multibyte chars in the scheme
    /// prefix correctly.
    #[test]
    fn utf8_url_userinfo_multibyte_scheme_no_panic() {
        // CJK glued to a credential URL — the scheme_start walker must not place
        // the start inside a multibyte codepoint.
        let cases = [
            "🔑postgresql://dbuser:S3cr3tP4ss@db.example.com/db", // gitleaks:allow
            "密钥mysql://root:hunter2pw@10.0.0.1:3306/app",       // gitleaks:allow
            "éredis://svc:V3ryS3cretPw@cache.internal:6379",      // gitleaks:allow
        ];
        for text in &cases {
            // Must not panic and must detect the credential.
            let result = scan(text);
            assert!(
                result.is_some(),
                "URL credential after multibyte must be caught: {text:?}"
            );
        }
    }

    /// `check_entropy_heuristic` window slicing with multibyte content at the
    /// ±TRIGGER_WINDOW boundary: `floor_char_boundary` must prevent slicing
    /// on a non-char boundary.
    #[test]
    fn utf8_entropy_window_multibyte_boundary_no_panic() {
        // Construct content where the TRIGGER_WINDOW (120 bytes) boundary falls
        // inside a 3-byte CJK character.  Repeat "数" (U+6570 = 3 bytes) to fill
        // exactly 119 bytes, then add an ASCII trigger word + high-entropy token.
        // Window start: token_offset - 120 = lands inside one of the CJK chars.
        let cjk_fill = "数".repeat(39); // 39 × 3 = 117 bytes
        assert_eq!(cjk_fill.len(), 117);
        // Pad with 2 more ASCII chars ("xy") so that the 120-byte window lands at
        // byte 119 which is the second byte of the 40th "数" — mid-multibyte.
        let secret = "Xk9mZ2vQpLrT8nJwYuAeHfBsDcGiONvM1"; // gitleaks:allow
        let content = format!("{cjk_fill}xy key {secret}");
        let _ = scan(&content); // must not panic

        // Also test the right edge: token ends at byte offset, window_end =
        // token_offset + raw_token.len() + 120 may land mid-multibyte.
        let content2 = format!("key {secret}{cjk_fill}xy");
        let _ = scan(&content2); // must not panic
    }

    /// `check()` top-level fuzz: a large batch of inputs with multibyte
    /// characters at various offsets to catch any remaining panic sites.
    /// All results must be either Ok or Err (not a panic).
    #[test]
    fn utf8_no_panic_property_test() {
        let multibyte_items = [
            "🔑",       // 4-byte emoji
            "密",       // 3-byte CJK
            "é",        // 2-byte accented Latin
            "\u{3000}", // 3-byte ideographic space
            "🇺🇸",       // 8-byte emoji flag (two surrogate-like scalars)
        ];
        let secrets = [
            "AKIAFAKEKEY00000000000000",
            "ghp_AAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAA",
            "sk-ant-api03-AAAAAAAAAAAAAAA",
            "Xk9mZ2vQpLrT8nJwYuAeHfBsDcGiONvM1",
            "FlyV1 fm2_AAAABBBBCCCCDDDDEEEEFFFF",
        ];
        for mb in &multibyte_items {
            for secret in &secrets {
                for sep in &["", " ", "\n"] {
                    // multibyte before secret
                    let s = format!("{mb}{sep}{secret}");
                    let _ = check(&s);
                    // multibyte after secret
                    let s = format!("{secret}{sep}{mb}");
                    let _ = check(&s);
                    // multibyte both sides
                    let s = format!("{mb}{sep}{secret}{sep}{mb}");
                    let _ = check(&s);
                    // repeated multibyte filling TRIGGER_WINDOW boundary
                    let fill = mb.repeat(50);
                    let s = format!("{fill} api_key {secret} {fill}");
                    let _ = check(&s);
                }
            }
        }
    }

    // ── mask_secrets: in-place redaction reusing the canonical detector ───────

    #[test]
    fn mask_secrets_borrows_clean_text() {
        let clean = "The FlashAttention paper introduces IO-aware tiling.";
        let masked = mask_secrets(clean);
        assert!(
            matches!(masked, std::borrow::Cow::Borrowed(_)),
            "clean text must not allocate"
        );
        assert_eq!(masked, clean);
    }

    #[test]
    fn mask_secrets_redacts_shapes_the_old_mirror_regex_missed() {
        // These are exactly the detectors the session mirror's previous local
        // regex did NOT cover, which is why it now shares this masker.
        let cases = [
            "key: sk-proj-FAKEKEY00000000000000000000000000000000", // gitleaks:allow
            "cred ASIAFAKEKEY00000000000",                          // gitleaks:allow
            "stripe sk_live_FAKESTRIPE0000000000000",               // gitleaks:allow
            "db postgresql://dbuser:S3cr3tP4ss@db.example.com/db",  // gitleaks:allow
        ];
        for c in &cases {
            let masked = mask_secrets(c);
            assert!(
                masked.contains(REDACTION_MARKER),
                "must redact: {c:?} -> {masked:?}"
            );
        }
    }

    #[test]
    fn mask_secrets_redacts_every_span_and_keeps_prose() {
        let line =
            "first sk-ant-api03-AAAAAAAAAAAAAAA then ghp_AAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAA end";
        let masked = mask_secrets(line);
        assert!(
            !masked.contains("sk-ant-api03") && !masked.contains("ghp_AAAA"),
            "no secret may survive: {masked}"
        );
        assert_eq!(
            masked.matches(REDACTION_MARKER).count(),
            2,
            "both secrets must be redacted: {masked}"
        );
        assert!(masked.starts_with("first "), "prose preserved: {masked}");
        assert!(masked.ends_with(" end"), "prose preserved: {masked}");
    }

    #[test]
    fn mask_secrets_output_passes_check() {
        // The masked output must itself be clean — no credential left for the
        // write-time gate to catch.
        let line = "token=ghp_AAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAA and AKIAFAKEKEY1234567890";
        let masked = mask_secrets(line).into_owned();
        assert!(
            check(&masked).is_ok(),
            "masked output must pass the gate: {masked}"
        );
    }

    #[test]
    fn mask_secrets_redacts_entropy_secret_left_of_known_secret() {
        // Cross-layer leftmost regression: a Layer-2 entropy secret sits to the
        // LEFT of a Layer-1 known-prefix secret. A scan that short-circuits on
        // the first known match (or returns first-by-detector-priority) would
        // redact `ghp_…` and copy the entropy token before it verbatim — leaking
        // it. `scan_match` must fold both layers through leftmost selection.
        let line =
            "secret=Xk9mZ2vQpLrT8nJwYuAeHfBsDcGiONvM and ghp_AAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAA"; // gitleaks:allow
        let masked = mask_secrets(line).into_owned();
        assert!(
            !masked.contains("Xk9mZ2vQpLrT8nJwYuAeHfBsDcGiONvM") && !masked.contains("ghp_AAAA"),
            "neither the entropy secret nor the known secret may survive: {masked}"
        );
        assert_eq!(
            masked.matches(REDACTION_MARKER).count(),
            2,
            "both secrets must be redacted exactly once: {masked}"
        );
        assert!(
            check(&masked).is_ok(),
            "masked output must pass the gate: {masked}"
        );
    }

    #[test]
    fn github_app_token_families_are_masked() {
        // ghu_ (user-to-server), ghs_ (server-to-server), and ghr_ (refresh)
        // GitHub App tokens are real credential families. They are
        // context-free: no trigger word needed.
        let cases = [
            "ghu_AAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAA", // gitleaks:allow
            "ghs_BBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBB",  // gitleaks:allow
            "ghr_CCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCC",  // gitleaks:allow
        ];
        for token in &cases {
            assert!(
                check(token).is_err(),
                "gate must hard-block GitHub App token {token}"
            );
            let line = format!("auth: {token} trailing");
            let masked = mask_secrets(&line).into_owned();
            assert!(
                !masked.contains(token),
                "GitHub App token must not survive masking: {masked}"
            );
            assert!(
                check(&masked).is_ok(),
                "masked output must pass the gate: {masked}"
            );
        }
    }

    #[test]
    fn mask_secrets_redacts_entropy_token_whose_trigger_is_left_of_earlier_secret() {
        // The entropy detector only fires near a
        // trigger word. When the trigger (`api_key`) sits to the LEFT of an
        // earlier known-prefix secret (`ghp_…`), a masker that rescans only the
        // suffix after each redaction loses that context and leaks the later
        // high-entropy token. Spans must be discovered against the ORIGINAL text.
        let line =
            "api_key ghp_AAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAA Xk9mZ2vQpLrT8nJwYuAeHfBsDcGiONvM1"; // gitleaks:allow
        let masked = mask_secrets(line).into_owned();
        assert!(
            !masked.contains("ghp_AAAA"),
            "the known secret must be redacted: {masked}"
        );
        assert!(
            !masked.contains("Xk9mZ2vQpLrT8nJwYuAeHfBsDcGiONvM1"),
            "the later entropy token must be redacted even though its trigger \
             word sits left of the earlier redaction: {masked}"
        );
        assert_eq!(
            masked.matches(REDACTION_MARKER).count(),
            2,
            "both secrets must be redacted exactly once: {masked}"
        );
        assert!(
            check(&masked).is_ok(),
            "masked output must pass the gate: {masked}"
        );
    }

    // ── Structured-identifier exemption: file paths / branch names ──────────
    //
    // The entropy heuristic tokenizes on whitespace, so a full file path is
    // one long token, and mixed-case+digit+punctuation paths can legitimately
    // exceed the Shannon-entropy threshold. The structured-identifier
    // exemption does not apply in trigger context (see the module doc): no
    // sound signal separates a real path from an attacker-chopped/padded
    // credential once Shannon entropy is the only measure and the attacker
    // controls run boundaries. The three cases below are accepted false
    // positives: their own full-token entropy exceeds ENTROPY_THRESHOLD, so
    // they block near a trigger word.

    #[test]
    fn blocks_file_path_near_secret_word_accepted_fp_round4() {
        // Full-token entropy 4.5994 > ENTROPY_THRESHOLD (4.5).
        let content =
            "workspace path fable-ops/ADR-DRAFT-adr079-slices234.md for the secret gate bug";
        assert!(
            check(content).is_err(),
            "accepted FP post round-4: structured file path near 'secret' is now \
             blocked; got {:?}",
            scan(content)
        );
    }

    #[test]
    fn blocks_workspace_path_near_key_word_accepted_fp_round4() {
        // Full-token entropy 4.7938 > 4.5.
        let content = "key: see internal/workspaces/20260701/adr079-slices234/PACKET.md";
        assert!(
            check(content).is_err(),
            "accepted FP post round-4: workspace path near 'key' is now blocked; \
             got {:?}",
            scan(content)
        );
    }

    #[test]
    fn blocks_short_run_path_near_auth_word_accepted_fp_round4() {
        // Full-token entropy 4.5955 > 4.5.
        let content =
            "auth work saved at internal/workspaces/20260701/cloud-rebuild/R1-repo-audit.md";
        assert!(
            check(content).is_err(),
            "accepted FP post round-4: path with a short 'R1' run near 'auth' is \
             now blocked; got {:?}",
            scan(content)
        );
    }

    #[test]
    fn allows_branch_and_review_filename_near_key_word() {
        let content =
            "branch feat-session-mirror pushed, see review_pr335_round2.md for the key findings";
        assert!(
            check(content).is_ok(),
            "branch name and review filename near 'key' must not be blocked; fired: {:?}",
            scan(content)
        );
    }

    #[test]
    fn allows_adr_doc_path_near_password_word() {
        let content = "password reset doc: docs/adr/ADR-055-epistemic-edge-relations.md";
        assert!(
            check(content).is_ok(),
            "ADR doc path near 'password' must not be blocked; fired: {:?}",
            scan(content)
        );
    }

    #[test]
    fn allows_source_file_path_near_credential_word() {
        let content = "credential handling code crates/khive-pack-session/src/mirror/ingest.rs";
        assert!(
            check(content).is_ok(),
            "source file path near 'credential' must not be blocked; fired: {:?}",
            scan(content)
        );
    }

    #[test]
    fn allows_long_snake_case_identifier_near_key_word() {
        let content = "api key handling lives in check_entropy_heuristic_impl";
        assert!(
            check(content).is_ok(),
            "snake_case identifier near 'key' must not be blocked; fired: {:?}",
            scan(content)
        );
    }

    // ── Structured-identifier exemption: catch-suite regression ─────────────

    #[test]
    fn hyphenated_random_secret_is_not_a_structured_identifier() {
        // Same token as `blocks_bare_base64url_43chars_near_key`: hyphenated
        // but not word-shaped. The second run exceeds the 24-char run cap,
        // and the first run's case-transition density (~0.42) exceeds the
        // 0.3 threshold on its own, so this must not be exempted and the
        // existing catch-suite test must keep blocking it.
        assert!(!is_structured_identifier(
            "wJalrXUtnFEMI-K7MDENGbPxRfiCYEXAMPLEKEYX123"
        ));
        let line = "api key wJalrXUtnFEMI-K7MDENGbPxRfiCYEXAMPLEKEYX123";
        assert!(
            scan(line).is_some(),
            "hyphenated random secret must still be blocked; got: {:?}",
            scan(line)
        );
    }

    // ── Structured-identifier exemption: direct unit tests ───────────────────

    #[test]
    fn structured_identifier_true_for_repro_paths() {
        let paths = [
            "fable-ops/ADR-DRAFT-adr079-slices234.md",
            "internal/workspaces/20260701/adr079-slices234/PACKET.md",
            "internal/workspaces/20260701/cloud-rebuild/R1-repo-audit.md",
            "review_pr335_round2.md",
            "docs/adr/ADR-055-epistemic-edge-relations.md",
            "crates/khive-pack-session/src/mirror/ingest.rs",
            "check_entropy_heuristic_impl",
        ];
        for p in paths {
            assert!(
                is_structured_identifier(p),
                "expected structured identifier: {p}"
            );
        }
    }

    #[test]
    fn structured_identifier_false_without_separator() {
        // No `/`, `-`, `_`, or `.` present — fails rule 1 outright.
        assert!(!is_structured_identifier(
            "Xk9mZ2vQpLrT8nJwYuAeHfBsDcGiONvM"
        ));
    }

    #[test]
    fn structured_identifier_false_for_leetspeak_digit_interleaving() {
        // Digits interleaved with letters within a run (not a trailing digit
        // suffix) fail the `[A-Za-z]+[0-9]*` / `[0-9]+` shape check.
        assert!(!is_structured_identifier("S3cr3t-P4ssw0rd-t0ken-here!"));
    }

    #[test]
    fn structured_identifier_false_for_run_over_length_cap() {
        // A 26-char single alphabetic run between separators fails the
        // 24-char per-run length cap even though it is otherwise trivially
        // word-shaped (uniform lowercase, zero case transitions).
        let long_run = "a".repeat(26);
        let token = format!("prefix-{long_run}-suffix");
        assert!(!is_structured_identifier(&token));
    }

    // ── Structured-identifier exemption drops entirely in trigger context ───
    //
    // Narrower fixes that keep some exemption alive in trigger context (e.g.
    // requiring a trailing file-extension run, or requiring >= 2 path-shaped
    // runs with a low average per-run letters-only entropy) are all
    // attacker-defeatable: a random credential can be extension-suffixed, or
    // split/padded into short runs that drive each run's own entropy toward
    // its length ceiling (log2(run_len)), which real short path words already
    // sit at. Shannon entropy over an attacker-chosen run boundary cannot
    // distinguish "distinct letters that spell an English word" from
    // "distinct letters chosen adversarially" — both hit the same
    // log2(length) ceiling, so no aggregation is sound. The exemption is
    // therefore dropped unconditionally in trigger context: a
    // structured-identifier-shaped token near a trigger word is
    // entropy-checked like any other token, with 3 known false positives
    // accepted (see `accepted_false_positive_*` below).

    #[test]
    fn blocks_separator_secret_access_key_bypass() {
        // Adversarial bypass shape: an AWS-secret-key-like value split into
        // separator-delimited word-shaped runs to dodge the entropy check.
        let content = "secret_access_key abcdefghij/klmnopqrst/uvwxyzabcd/efghijk";
        assert!(
            check(content).is_err(),
            "AWS Secret Access Key shaped bypass must be blocked: {:?}",
            scan(content)
        );
    }

    #[test]
    fn blocks_adversarial_lowercase_only_separator_token_near_access_key() {
        let content = "access_key qrstuvwxyz/abcdefghij/klmnopqrst/uvwxyzab";
        assert!(
            check(content).is_err(),
            "lowercase-only separator-delimited high-entropy token near \
             'access_key' must be blocked: {:?}",
            scan(content)
        );
    }

    #[test]
    fn blocks_adversarial_digit_and_word_mixed_token_near_api_key() {
        // A mix of pure-digit runs and letters-then-digits runs (both
        // individually word-shaped) whose combined alphabet diversity crosses
        // the entropy threshold.
        let content = "api_key attaycofrsm827/festwqjhc493/8261947350/qwikjzx982";
        assert!(
            check(content).is_err(),
            "digit-and-word-mixed high-entropy token near 'api_key' must be blocked: {:?}",
            scan(content)
        );
    }

    #[test]
    fn blocks_adversarial_token_assignment_separator_delimited_secret() {
        let content = "token=zxkqwmvbpl/trfhysjgnc/dweiaoutkz-mnbvcxzlk";
        assert!(
            check(content).is_err(),
            "token= with lowercase-only separator-delimited high-entropy value \
             must be blocked: {:?}",
            scan(content)
        );
    }

    #[test]
    fn blocks_extension_suffix_bypass_secret_access_key() {
        // A file-extension check alone would exempt this: appending `.md`
        // to a random credential must not bypass detection.
        let content = "secret_access_key abcdefghij/klmnopqrst/uvwxyzabcd/efghijk.md";
        assert!(
            check(content).is_err(),
            "extension-suffixed AWS Secret Access Key shaped bypass must be blocked: {:?}",
            scan(content)
        );
    }

    #[test]
    fn blocks_extension_suffix_bypass_token_assignment() {
        let content = "token=zxkqwmvbpl/trfhysjgnc/dweiaoutkz-mnbvcxzlk.rs";
        assert!(
            check(content).is_err(),
            "extension-suffixed token= bypass must be blocked: {:?}",
            scan(content)
        );
    }

    #[test]
    fn blocks_round1_bypass_strings_still_without_extension() {
        let cases = [
            "secret_access_key abcdefghij/klmnopqrst/uvwxyzabcd/efghijk",
            "token=zxkqwmvbpl/trfhysjgnc/dweiaoutkz-mnbvcxzlk",
        ];
        for content in cases {
            assert!(
                check(content).is_err(),
                "round-1 bypass string must still be blocked: {content:?}, got: {:?}",
                scan(content)
            );
        }
    }

    #[test]
    fn blocks_digit_run_suffix_bypass_attempt() {
        let cases = [
            "secret_access_key abcdefghij/klmnopqrst/uvwxyzabcd/efghijk2024",
            "secret_access_key abcdefghij2024/klmnopqrst/uvwxyzabcd/efghijk.md",
        ];
        for content in cases {
            assert!(
                check(content).is_err(),
                "digit-run-suffixed bypass attempt must be blocked: {content:?}, got: {:?}",
                scan(content)
            );
        }
    }

    #[test]
    fn blocks_round3_padding_run_bypass_attempts() {
        // A low-entropy padding run (`aaaa`) inserted before short/digit-shaped
        // runs would drag any AVERAGE per-run entropy signal below its
        // threshold. With the exemption dropped entirely, these must be
        // blocked purely on full-token entropy, same as any other
        // near-trigger high-entropy token.
        let cases = [
            "secret_access_key abcdefghij/klmnopqrst/uvwxyzabcd/efghijk/aaaa/R1.md",
            "token=zxkqwmvbpl/trfhysjgnc/dweiaoutkz/mnbvcxzlk/aaaa/R1.rs",
            "secret_access_key abcdefghij/klmnopqrst/uvwxyzabcd/efghijk/aaaa/bbbb/R1.md",
            "token=zxkqwmvbpl/trfhysjgnc/dweiaoutkz/mnbvcxzlk/aaaa/bbbb/R1.rs",
        ];
        for content in cases {
            assert!(
                check(content).is_err(),
                "round-3 padding-run bypass attempt must be blocked: {content:?}, got: {:?}",
                scan(content)
            );
        }
    }

    #[test]
    fn blocks_run_splitting_bypass_attempts() {
        // Splitting a credential into short (4-6 char) runs drives EVERY
        // run's own letters-only entropy toward log2(run_len), which ordinary
        // short English path words already sit at or near: this is exactly
        // why any per-run entropy ceiling is unsound as an exemption signal.
        // With the exemption dropped, these are blocked on full-token entropy
        // regardless of run shape.
        let cases = [
            "secret_access_key abcd/efgh/ijkl/mnop/qrst/uvwx/yzab/cdef.md",
            "secret_access_key abcde/fghij/klmno/pqrst/uvwxy/zabcd.md",
            "secret_access_key abcdef/ghijkl/mnopqr/stuvwx/yzabcd.md",
        ];
        for content in cases {
            assert!(
                check(content).is_err(),
                "run-splitting bypass attempt must be blocked: {content:?}, got: {:?}",
                scan(content)
            );
        }
    }

    #[test]
    fn allows_fp_paths_whose_full_token_entropy_is_already_below_threshold() {
        // 4 of the 7 original FP-repro paths stay OK near a trigger word even
        // with NO structured-identifier exemption at all, because their own
        // full-token Shannon entropy already reads below ENTROPY_THRESHOLD
        // (4.5) — the exemption was never load-bearing for these regardless
        // of which version of it existed.
        let paths = [
            "review_pr335_round2.md",
            "docs/adr/ADR-055-epistemic-edge-relations.md",
            "crates/khive-pack-session/src/mirror/ingest.rs",
            "check_entropy_heuristic_impl",
        ];
        for p in paths {
            let content = format!("api_key handling in {p}");
            assert!(
                check(&content).is_ok(),
                "{p} must stay allowed near 'api_key' (full-token entropy already \
                 below threshold): fired {:?}",
                scan(&content)
            );
        }
    }

    #[test]
    fn accepted_false_positive_adr_draft_path_near_trigger() {
        // Accepted tradeoff: this path's full-token Shannon entropy (4.5994)
        // exceeds ENTROPY_THRESHOLD (4.5) on its own. With the
        // structured-identifier exemption dropped in trigger context, it is
        // blocked near an explicit credential trigger word: a deliberate,
        // documented false positive, not a regression to fix, since no sound
        // signal exists to distinguish this from a chopped/padded credential
        // of the same shape.
        let content = "api_key handling in fable-ops/ADR-DRAFT-adr079-slices234.md";
        assert!(
            check(content).is_err(),
            "accepted FP: ADR-DRAFT path near 'api_key' is now blocked post round-4; \
             got {:?}",
            scan(content)
        );
    }

    #[test]
    fn accepted_false_positive_workspace_packet_path_near_trigger() {
        // Same tradeoff as above: full-token entropy 4.7938 > 4.5.
        let content = "api_key handling in internal/workspaces/20260701/adr079-slices234/PACKET.md";
        assert!(
            check(content).is_err(),
            "accepted FP: PACKET.md workspace path near 'api_key' is now blocked \
             post round-4; got {:?}",
            scan(content)
        );
    }

    #[test]
    fn accepted_false_positive_r1_repo_audit_path_near_trigger() {
        // Same tradeoff as above: full-token entropy 4.5955 > 4.5.
        let content =
            "api_key handling in internal/workspaces/20260701/cloud-rebuild/R1-repo-audit.md";
        assert!(
            check(content).is_err(),
            "accepted FP: R1-repo-audit path near 'api_key' is now blocked post \
             round-4; got {:?}",
            scan(content)
        );
    }

    // ── UUID / content-hash allowlists are prose-context only ───────────────

    #[test]
    fn blocks_uuid_directly_labeled_as_api_key() {
        let content = "api_key 550e8400-e29b-41d4-a716-446655440000";
        assert!(
            check(content).is_err(),
            "UUID-shaped token labeled api_key must be blocked; got {:?}",
            scan(content)
        );
    }

    #[test]
    fn blocks_sha256_content_hash_labeled_as_secret() {
        let content = "secret sha256-ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopq";
        assert!(
            check(content).is_err(),
            "sha256-prefixed hash labeled secret must be blocked; got {:?}",
            scan(content)
        );
    }

    #[test]
    fn blocks_sha384_content_hash_labeled_as_api_key() {
        let content =
            "api_key sha384-ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz0123456789+/";
        assert!(
            check(content).is_err(),
            "sha384-prefixed hash labeled api_key must be blocked; got {:?}",
            scan(content)
        );
    }

    #[test]
    fn blocks_sha512_content_hash_labeled_as_auth() {
        let content = "auth sha512-ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz0123456789+/ABCDEFGHIJKLMNOPQRSTUV";
        assert!(
            check(content).is_err(),
            "sha512-prefixed hash labeled auth must be blocked; got {:?}",
            scan(content)
        );
    }

    #[test]
    fn allows_uuid_with_no_trigger_within_window() {
        // Common benign shape: a UUID (e.g. an internal record id) with no
        // credential trigger word anywhere in the surrounding window stays
        // allowed — the allowlist still applies outside trigger context.
        let content =
            "task 550e8400-e29b-41d4-a716-446655440000 was created and assigned to the team";
        assert!(
            check(content).is_ok(),
            "UUID with no nearby trigger word must stay allowed; got {:?}",
            scan(content)
        );
    }

    #[test]
    fn allows_internal_area_id_uuid_near_auth_substring_round5() {
        // An internal task `area_id` UUID field sitting within the trigger
        // window of the SUBSTRING "auth" inside
        // `authorized_write_requires_dominance` is not a genuine mention of
        // the word "auth": it is a pure substring collision with
        // "authorized". Bare trigger words match at a word boundary (see
        // `contains_bounded_word`), so `auth` does not match inside
        // `authorized`; this UUID has no trigger in its window and passes via
        // the ordinary out-of-context UUID allowlist.
        let content = "area_id: cfcea31d-6f50-4fd1-ad6d-5f160de1694c\n\n## Problem\nReduce Lion microkernel axioms. Converted authorized_write_requires_dominance from axiom to theorem.";
        assert!(
            check(content).is_ok(),
            "round-5 fix: internal area_id UUID near the 'authorized' substring \
             (not a genuine 'auth' mention) must now pass; got {:?}",
            scan(content)
        );
    }

    // ── UUID/hash value extraction from assignment and wrapper syntax ───────

    #[test]
    fn blocks_uuid_glued_to_assignment_equals() {
        let content = "api_key=550e8400-e29b-41d4-a716-446655440000";
        assert!(
            check(content).is_err(),
            "UUID glued via '=' to a trigger word must be blocked; got {:?}",
            scan(content)
        );
    }

    #[test]
    fn blocks_uuid_with_trailing_sentence_period() {
        let content = "api_key 550e8400-e29b-41d4-a716-446655440000.";
        assert!(
            check(content).is_err(),
            "UUID with a trailing sentence period near a trigger must be blocked; got {:?}",
            scan(content)
        );
    }

    #[test]
    fn blocks_uuid_wrapped_in_parens() {
        let content = "api_key (550e8400-e29b-41d4-a716-446655440000)";
        assert!(
            check(content).is_err(),
            "UUID wrapped in parens near a trigger must be blocked; got {:?}",
            scan(content)
        );
    }

    #[test]
    fn blocks_uuid_in_json_object() {
        let content = "{\"api_key\":\"550e8400-e29b-41d4-a716-446655440000\"}";
        assert!(
            check(content).is_err(),
            "UUID in a JSON-ish object near a trigger key must be blocked; got {:?}",
            scan(content)
        );
    }

    #[test]
    fn blocks_content_hash_glued_to_assignment_equals() {
        let content = "secret=sha256-ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopq";
        assert!(
            check(content).is_err(),
            "sha256-prefixed hash glued via '=' to a trigger word must be blocked; \
             got {:?}",
            scan(content)
        );
    }

    #[test]
    fn blocks_content_hash_with_trailing_sentence_period() {
        let content = "secret sha256-ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopq.";
        assert!(
            check(content).is_err(),
            "sha256-prefixed hash with a trailing period near a trigger must be \
             blocked; got {:?}",
            scan(content)
        );
    }

    #[test]
    fn blocks_content_hash_wrapped_in_parens() {
        let content = "secret (sha256-ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopq)";
        assert!(
            check(content).is_err(),
            "sha256-prefixed hash wrapped in parens near a trigger must be blocked; \
             got {:?}",
            scan(content)
        );
    }

    #[test]
    fn blocks_content_hash_in_json_object() {
        let content = "{\"secret\":\"sha256-ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopq\"}";
        assert!(
            check(content).is_err(),
            "sha256-prefixed hash in a JSON-ish object near a trigger key must be \
             blocked; got {:?}",
            scan(content)
        );
    }

    #[test]
    fn allows_uuid_wrapped_in_parens_with_no_trigger_nearby() {
        // Control: the prose allowlist must survive for wrapper syntax when
        // there is no credential trigger word anywhere in the window — only
        // the trigger-context extraction changed, not the outside-context
        // allowlist itself.
        let content = "wrapper (550e8400-e29b-41d4-a716-446655440000) present";
        assert!(
            check(content).is_ok(),
            "UUID wrapped in parens with no trigger word nearby must stay allowed; \
             got {:?}",
            scan(content)
        );
    }

    #[test]
    fn blocks_padded_content_hash_glued_to_assignment_with_trailing_period() {
        // A padded base64 value ends in its own `=`, which is also a valid
        // separator character — `value_candidates` must enumerate the
        // suffix after every `=`/`:`, not assume any single separator
        // position, so the true value is recovered regardless of which
        // separator happens to sit where.
        let content = "secret=sha256-AAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAA=.";
        assert!(
            check(content).is_err(),
            "padded sha256 hash glued via '=' with a trailing period must be \
             blocked; got {:?}",
            scan(content)
        );
    }

    #[test]
    fn blocks_padded_content_hash_in_json_object() {
        let content = "{\"secret\":\"sha256-AAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAA=\"}";
        assert!(
            check(content).is_err(),
            "padded sha256 hash in a JSON-ish object near a trigger key must be \
             blocked; got {:?}",
            scan(content)
        );
    }

    #[test]
    fn blocks_uuid_when_json_label_itself_contains_colon() {
        // The label can itself contain the separator character
        // (`"api:key"` rather than `"api_key"`); the first `:` after
        // wrapper-stripping then lands inside the label, not at the
        // label/value boundary. value_candidates must still surface the
        // bare UUID as a later suffix candidate.
        let content = "{\"api:key\":\"550e8400-e29b-41d4-a716-446655440000\"}";
        assert!(
            check(content).is_err(),
            "UUID must be blocked even when the JSON label contains ':'; got {:?}",
            scan(content)
        );
    }

    #[test]
    fn blocks_uuid_when_json_label_itself_contains_equals() {
        let content = "{\"api=key\":\"550e8400-e29b-41d4-a716-446655440000\"}";
        assert!(
            check(content).is_err(),
            "UUID must be blocked even when the JSON label contains '='; got {:?}",
            scan(content)
        );
    }

    #[test]
    fn blocks_uuid_behind_doubled_assignment() {
        // key=label=value: the first `=` lands between two labels, not at
        // the true value boundary.
        let content = "api_key=label=550e8400-e29b-41d4-a716-446655440000"; // gitleaks:allow
        assert!(
            check(content).is_err(),
            "UUID must be blocked behind a doubled assignment; got {:?}",
            scan(content)
        );
    }

    #[test]
    fn blocks_padded_content_hash_behind_doubled_assignment_equals() {
        let content = "secret=label=sha256-AAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAA=.";
        assert!(
            check(content).is_err(),
            "padded content hash must be blocked behind a doubled '=' assignment; \
             got {:?}",
            scan(content)
        );
    }

    #[test]
    fn blocks_padded_content_hash_behind_doubled_assignment_colon() {
        let content = "secret:label=sha256-AAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAA=.";
        assert!(
            check(content).is_err(),
            "padded content hash must be blocked behind a doubled ':'+'=' \
             assignment; got {:?}",
            scan(content)
        );
    }

    #[test]
    fn allows_benign_url_with_scheme_and_path_separators() {
        // `value_candidates`'s any-suffix semantics must not block ordinary
        // URLs, whose `://` and `/` characters produce several suffix
        // candidates but none of them are UUID- or content-hash-shaped.
        // Placed near a real trigger word ("key") so the check actually
        // exercises the trigger-context path rather than being skipped
        // outright.
        let content = "api_key endpoint=https://example.test/resource/for/testing";
        assert!(
            check(content).is_ok(),
            "a benign URL near a trigger word must stay allowed; got {:?}",
            scan(content)
        );
    }

    // ── Trigger word-boundary matching ──────────────────────────────────────

    #[test]
    fn allows_authorized_and_authentication_prose_near_uuid() {
        // The word-boundary fix directly: "auth" no longer matches the
        // substring inside "authorized"/"authentication", so ordinary prose
        // using those words does not poison the trigger window for a nearby
        // UUID or other allowlisted shape.
        let cases = [
            "authorized_write_requires_dominance was converted from axiom to theorem, id 550e8400-e29b-41d4-a716-446655440000",
            "authentication flow diagram lives at 550e8400-e29b-41d4-a716-446655440000",
        ];
        for content in cases {
            assert!(
                check(content).is_ok(),
                "'authorized'/'authentication' substring must not trigger the \
                 entropy heuristic: {content:?}, got {:?}",
                scan(content)
            );
        }
    }

    #[test]
    fn allows_turkey_monkey_keyword_prose_near_uuid() {
        // Other bare-word substring collisions in TRIGGER_WORDS ("key") must
        // likewise not fire on ordinary English words that merely contain it.
        let cases = [
            "the turkey and monkey story references id 550e8400-e29b-41d4-a716-446655440000",
            "keyword research doc: 550e8400-e29b-41d4-a716-446655440000",
        ];
        for content in cases {
            assert!(
                check(content).is_ok(),
                "'turkey'/'monkey'/'keyword' substring must not trigger the \
                 entropy heuristic: {content:?}, got {:?}",
                scan(content)
            );
        }
    }

    #[test]
    fn blocks_standalone_auth_and_key_words_unchanged_by_round5() {
        // Word-boundary matching only removes SUBSTRING collisions; a genuine
        // standalone trigger word must still dominate exactly as before.
        let opaque = "Xk9mZ2vQpLrT8nJwYuAeHfBsDcGiONvMabcdef"; // gitleaks:allow
        let cases = [
            format!("auth header {opaque}"),
            format!("the key is {opaque}"),
            format!("secret value: {opaque}"),
        ];
        for content in &cases {
            assert!(
                check(content).is_err(),
                "a genuine standalone trigger word must still block: {content:?}, \
                 got {:?}",
                scan(content)
            );
        }
    }

    #[test]
    fn accepted_false_positive_workspace_artifact_path_near_standalone_secret_round5() {
        // A dot-prefixed root + date segment + hyphenated topic dir +
        // SCREAMING_SNAKE filename, discussed in prose that genuinely (not by
        // substring collision) mentions "secret". `secret` here is a real
        // standalone word, not a substring collision, so it still dominates
        // and the path still falls through to the entropy heuristic like any
        // other near-trigger token. A documented accepted tradeoff, not a
        // regression.
        let content = "writing up the secret gate false positive repro: \
             .workspace/20260101/fix-secret-gate-trigger-false-positive/MEASUREMENT_REPORT.md";
        assert!(
            check(content).is_err(),
            "accepted FP (round 5 unchanged): workspace artifact path near a \
             genuine standalone 'secret' mention is still blocked; got {:?}",
            scan(content)
        );
    }

    #[test]
    fn accepted_false_positive_archive_doc_path_near_standalone_secret_round5() {
        // An archive-style doc path discussed near a genuine standalone
        // "secret" mention.
        let content =
            "secret scanner archive notes: docs/_archive/ADR051-TenantEncryption-v2Notes.md";
        assert!(
            check(content).is_err(),
            "accepted FP (round 5 unchanged): archive doc path near a genuine \
             standalone 'secret' mention is still blocked; got {:?}",
            scan(content)
        );
    }

    #[test]
    fn accepted_false_positive_absolute_path_near_standalone_auth_round5() {
        // An absolute path written as one unbroken token, with the
        // surrounding message genuinely (not via substring collision)
        // discussing "auth".
        let content = "the auth scanner flagged this file: /home/user/projects/workspace/SessionNotes20260107/AuthGateFollowup2.md";
        assert!(
            check(content).is_err(),
            "accepted FP (round 5 unchanged): absolute path near a genuine \
             standalone 'auth' mention is still blocked; got {:?}",
            scan(content)
        );
    }

    #[test]
    fn blocks_assignment_shaped_credential_disguised_as_path_near_api_key() {
        // Adversarial negative: a credential-shaped value glued via '='
        // directly to a trigger word must not be exempted just because it is
        // path-shaped (separator-delimited, word-shaped runs) and looks
        // superficially like the accepted-FP repro paths above. The compound
        // entry `api_key` is a plain substring match regardless of
        // word-boundary rules, and the structured-identifier exemption is
        // unconditionally dropped in trigger context, so this must block.
        let content = "api_key=/home/user/workspaces/2026/topic-name-example/SECRET_VALUE_HERE.md";
        assert!(
            check(content).is_err(),
            "assignment-shaped credential disguised as a path must still be \
             blocked: {content:?}, got {:?}",
            scan(content)
        );
    }

    #[test]
    fn blocks_secret_access_key_bypass_compound_entry_unaffected_by_round5() {
        // Adversarial negative: a separator-split bypass shape must still be
        // blocked. It fires via TWO independent paths: the compound
        // `access_key` entry (`COMPOUND_TRIGGER_WORDS`, plain substring,
        // always matched regardless of word-boundary rules), AND the bare
        // `secret` entry, because underscore is a BOUNDARY for bare
        // `TRIGGER_WORDS`: so `secret` in `secret_access_key` is itself a
        // bounded word (bounded by the following `_`), not merely a
        // substring collision. Either path alone is sufficient; this asserts
        // the end-to-end outcome.
        let content = "secret_access_key abcdefghij/klmnopqrst/uvwxyzabcd/efghijk.md";
        assert!(
            check(content).is_err(),
            "secret_access_key bypass shape must still be blocked: {content:?}, \
             got {:?}",
            scan(content)
        );
    }

    // ── Underscore is a BOUNDARY for bare TRIGGER_WORDS, not a continuation ─
    //
    // Bare TRIGGER_WORDS are word-boundary-aware, but underscore must be
    // treated as a boundary rather than a word character (continuation) for
    // this set specifically: the opposite of `has_standalone_token`'s rule
    // for `token`. Treating underscore as a continuation would silently drop
    // detection of extremely common underscore-joined credential-config
    // compounds (`SECRET_KEY=`, `auth_token=`, `signing_key=`,
    // `session_secret_...`), since `secret`/`key`/`auth` would never be
    // bounded by `_` under that rule. Fixed by treating `_` as a boundary for
    // the bare `TRIGGER_WORDS` check specifically (see `contains_word`'s
    // `underscore_is_word_char` parameter), while leaving
    // `has_standalone_token`'s `token`-specific underscore-as-continuation
    // rule (the `tokenizer`/`next_token`/`token_count` exemption) unchanged.

    #[test]
    fn blocks_django_style_secret_key_assignment_round5b() {
        // `SECRET_KEY=<value>` must block via the plain-substring `secret`
        // trigger even though `secret` is followed by `_` rather than a
        // non-word-char boundary.
        let content = "SECRET_KEY=dGhpc2lzYXNlY3JldGtleXZhbHVlMTIzNDU2Nzg5MA=="; // gitleaks:allow
        assert!(
            check(content).is_err(),
            "SECRET_KEY=<value> (Django/Flask-style config) must still be \
             blocked: {content:?}, got {:?}",
            scan(content)
        );
    }

    #[test]
    fn blocks_auth_token_assignment_round5b() {
        let opaque = "Xk9mZ2vQpLrT8nJwYuAeHfBsDcGiONvMabcdef"; // gitleaks:allow
        let content = format!("auth_token={opaque}");
        assert!(
            check(&content).is_err(),
            "auth_token=<value> must still be blocked: {content:?}, got {:?}",
            scan(&content)
        );
    }

    #[test]
    fn blocks_session_secret_and_signing_key_compounds_round5b() {
        let opaque = "Xk9mZ2vQpLrT8nJwYuAeHfBsDcGiONvMabcdef"; // gitleaks:allow
        let cases = [
            format!("session_secret_{opaque}"),
            format!("signing_key={opaque}"),
        ];
        for content in &cases {
            assert!(
                check(content).is_err(),
                "underscore-joined credential compound must still be blocked: \
                 {content:?}, got {:?}",
                scan(content)
            );
        }
    }

    #[test]
    fn allows_authorized_authentication_keyword_prose_unaffected_by_round5b() {
        // The letter-joined substring-collision exemption must survive the
        // underscore-as-boundary change, since that change only affects the
        // underscore character, not letter-joined words.
        let cases = [
            "authorized_write_requires_dominance was converted from axiom to theorem, id 550e8400-e29b-41d4-a716-446655440000",
            "authentication flow diagram lives at 550e8400-e29b-41d4-a716-446655440000",
            "the turkey and monkey story references id 550e8400-e29b-41d4-a716-446655440000",
            "keyword research doc: 550e8400-e29b-41d4-a716-446655440000",
        ];
        for content in cases {
            assert!(
                check(content).is_ok(),
                "letter-joined substring collision must stay exempt after \
                 round-5b: {content:?}, got {:?}",
                scan(content)
            );
        }
    }

    #[test]
    fn block_message_carries_actionable_guidance() {
        let fake = "AKIAFAKEKEY1234567890";
        let m = scan(fake).unwrap();
        let rendered = m.to_string();
        assert!(
            rendered.contains("real credential"),
            "block message must carry actionable guidance: {rendered}"
        );
    }

    #[test]
    fn block_message_shape_guidance_mentions_rewording() {
        let opaque = "Xk9mZ2vQpLrT8nJwYuAeHfBsDcGiONvMabcdef"; // gitleaks:allow
        let content = format!("auth header {opaque}");
        let m = scan(&content).unwrap();
        let rendered = m.to_string();
        assert!(
            rendered.contains("reword") || rendered.contains("own line"),
            "shape-based detector guidance must suggest rewording/splitting: {rendered}"
        );
    }
}

// ─── Corpus replay harness (manual, opt-in) ─────────────────────────────────
//
// Measures how many real note/entity strings the gate blocks, so a detector
// change can be evaluated against production content rather than intuition
// (see the module doc). Opens the target database
// STRICTLY read-only (`SQLITE_OPEN_READ_ONLY`) and never mutates it. Point
// `KHIVE_REPLAY_DB` at a copy or a live KG database file path; the harness
// never writes, locks aggressively, or deletes anything.
//
// Run with: `KHIVE_REPLAY_DB=/path/to/khive.db cargo test -p khive-runtime \
//   --release -- --ignored --nocapture corpus_replay`
#[cfg(test)]
mod corpus_replay {
    use super::*;
    use rusqlite::{Connection, OpenFlags};

    #[test]
    #[ignore]
    fn replay_against_corpus() {
        let db_path = std::env::var("KHIVE_REPLAY_DB")
            .expect("set KHIVE_REPLAY_DB=/path/to/khive.db to run the corpus replay (read-only)");
        let conn = Connection::open_with_flags(
            &db_path,
            OpenFlags::SQLITE_OPEN_READ_ONLY | OpenFlags::SQLITE_OPEN_NO_MUTEX,
        )
        .expect("open corpus DB read-only");

        let mut total = 0usize;
        let mut blocked = 0usize;
        let mut samples: Vec<String> = Vec::new();

        let mut collect = |sql: &str| {
            let mut stmt = conn.prepare(sql).expect("prepare replay query");
            let mut rows = stmt.query([]).expect("query replay rows");
            while let Some(row) = rows.next().expect("read replay row") {
                let content: Option<String> = row.get(0).unwrap_or(None);
                let Some(content) = content else { continue };
                if content.is_empty() {
                    continue;
                }
                total += 1;
                if let Some(m) = scan(&content) {
                    blocked += 1;
                    if samples.len() < 30 {
                        samples.push(format!(
                            "{} :: {}",
                            m,
                            content.chars().take(160).collect::<String>()
                        ));
                    }
                }
            }
        };

        collect("SELECT content FROM notes WHERE deleted_at IS NULL");
        collect("SELECT description FROM entities WHERE deleted_at IS NULL");

        eprintln!("corpus replay: {blocked}/{total} strings blocked");
        for s in &samples {
            eprintln!("  BLOCKED: {s}");
        }
    }
}