zernie__vigiles/docs/compiled-hooks.md

Compiled hooks — author a hook that can't be wrong

⚠️ Compiled hooks are experimental. They compile, they run in production in two repos, and every property below is tested — but the authoring vocabulary is not settled, and it is not covered by semver. The six entry points are named experimental_defineHook, experimental_defineFileGate, experimental_definePromptGate, experimental_defineStopGate, experimental_defineInject and experimental_defineReact. Write them out at every call site — do not alias the prefix away at the import. This notice used to advise exactly that, and the advice defeated the mechanism it was attached to: measured 2026-08-21, with the alias in place the marker survived at 0 of 5 call sites in the only user-facing example, because a reader 200 lines down sees defineHook(...) and cannot tell it is provisional. A prefix stripped on import is a subpath with extra steps. What would have to be true to drop the prefix.

Stable alternative: a hand-written shell hook wired in settings.json. Same events, same protocol, none of the guarantees this page is about.

A hook is the harness's deterministic gate: the one place that can stop the agent before it does something irreversible. But a hook today is opaque shell (bash guard.sh), and the parts you hand-write are exactly the parts that fail silently. The README has the pitch; this is the full guide.

vigiles lets you author a hook as a pure typed function (event) => Decision against a closed vocabulary (vigiles/hook), then compiles it to the harness protocol. The point isn't ergonomics — it's that whole classes of hook bugs become unrepresentable: you can't write the bug because the API has no way to express it.

Contents

• The bug classes it eliminates
• The roles
• The vocabulary
• Observe mode (shadow rollout)
• Deciding on external state (context providers)
• Compile and wire
• Where things live
• Testing a compiled hook
• Proof: the OSS dogfood
• Limitations & trade-offs (the cons)
• See also

The bug classes it eliminates

A compiled hook eliminates an entire class of bugs by construction — not by catching them after the fact, but by making them impossible to write. Each row below is a verified, common failure of hand-written hooks (sources linked):

Bug class	Why it can't happen
False confidence — the #1 pain: exit 1 instead of exit 2, the wrong JSON field (decision vs permissionDecision), a wrong jq path → a guard that looks like it blocks and silently allows (RFC #45427, #24327).	You never write the protocol. You return deny(reason); the compiler emits the correct exit code / JSON field for the event. The bug has no place to live.
Matcher bypass — Bash(git push:*) (or a hand-written grep) misses cd repo && git push -f (#30519).	command.runs("git push", { force: true }) is AST-backed — it sees the real git push leaf however it's wrapped (compound, subshell, pipeline). A grep false-positive is gone too.
Capability creep / supply chain — a hook is arbitrary code; a copied or edited one can read secrets or phone home (CVE-2025-59536).	Capability = API surface. An import of anything but vigiles/hook (or eval/Function) does not compile. The compiled artifact is stamped (SHA-256) — a later hand-edit breaks the stamp and the runtime refuses it.
Category mistakes — "block on a SessionStart/PostToolUse hook", whose decision is a documented no-op (#4362).	Each role has its own return type. An inject/react hook has no deny in its vocabulary, so the mistake is a tsc type error, not a silent no-op.

The unifying idea: a hook is a tiny program, and a closed, typed vocabulary shrinks its state space until the bad states are simply not expressible.

The roles

A hook's output depends on when it fires. vigiles gives each role its own builder and its own return type, so the wrong output for an event won't type-check:

• experimental_defineHook / experimental_defineFileGate — a tool gate (PreToolUse). Returns a Decision: allow(), deny(reason), or ask(reason). deny is the only thing that blocks; the compiler maps it to exit 2. experimental_defineHook sees the Bash command (e.command); experimental_defineFileGate sees the file path (e.path).
• experimental_definePromptGate — a prompt gate (UserPromptSubmit). Sees the prompt text (e.prompt) and returns a Decision. deny blocks/erases the prompt — useful as a security filter that refuses a prompt leaking a secret or carrying an injection.
• experimental_defineStopGate — a stop gate (Stop / SubagentStop). Returns a Decision. deny keeps the agent going (gate-until-tests-pass; the reason is fed back to the model). Honour e.stopHookActive (the loop guard): allow when it's set, or you can wedge the agent in a stop→continue loop.
• experimental_defineInject — an inject (SessionStart / UserPromptSubmit). Returns an Injection (inject(text)) — context added to the model. It has no deny: a no-decision event can't block.
• experimental_defineReact — a react (PostToolUse). Returns a Reaction — run(cmd), notice(msg), or nothing(). The tool already ran, so it can't block. It sees the tool's response (e.response, e.g. react only on a failure), and run(cmd)'s effect is classified at construction (read-only / side-effecting), so every reaction is auditable without running it.

Every gate (tool / prompt / stop) takes an optional mode — see Observe mode.

The vocabulary

The entire surface a hook may touch (that's the safety guarantee):

import { experimental_defineHook, tool, deny, allow } from "vigiles/hook";

// Block any force-push to a protected branch — including one hidden in a
// compound command, which a glob/grep matcher misses.
export default experimental_defineHook({
  on: "PreToolUse",
  match: tool("Bash"),
  decide: (e) =>
    e.command.runs("git push", { force: true })
      ? deny("no force-push to a protected branch")
      : allow(),
});

• tool(name) / tools(...names) — which tool(s) the hook matches.

• e.command (Bash) — an AST-backed CommandView:

  • runs(program, { force? }) — a leaf runs program (e.g. "git reset --hard"), optionally forced.
  • touches(prefixes) — a leaf mentions a path under one of prefixes (e.g. ["~/.ssh", ".env"]) — secret reads.
  • writesTo(prefixes) — a leaf creates or modifies a file under one of prefixes: redirection targets (cmd > f, >>, >|, &>) plus the writing argv position of sed -i, cp / mv / install (destination), tee, dd of=, truncate, shred.
  • writeTargets(prefixes) — the same write targets as the list of files rather than a boolean, for a gate that has to tell which file (writeTargets(PAPER_SOURCES).some(isPaperSource)); writesTo is exactly writeTargets(prefixes).length > 0. Spelling is as-written after normalization (quotes removed by the parser, $HOME canonicalized, a leaf's own env -C / sudo -D directory resolved), duplicates collapsed — so filter by basename or suffix. prefixes is required and there is no unfiltered form: a consumer holding the raw list has to re-implement prefix matching by hand, which is where every measured gate bypass came from.
  • pipesToShell() — pipes into a bare shell (curl … | sh) — remote-code execution. A shell with a script file (sh deploy.sh) is not flagged.
  • isSideEffecting() — the deterministic Bash-effect classifier's verdict.

  touches ≠ writesTo — conflating them is the trap. touches answers mentioned: grep -c x notes/S.md matches, and so does rm -rf notes. isSideEffecting() does not rescue it, because it classifies the whole command line — grep -c x notes/S.md 2>/dev/null is side-effecting (there's a redirection), so a touches() && isSideEffecting() gate blocks a plain read. Use writesTo to gate writes and touches for "don't even look at this path". Deletion is reported by neither — pair with runs("rm") if a gate needs it.

  Both are DENYLISTS, so they over-block on purpose — the opposite bias from under below. A miss here is an allow, not silence, so an answer the matcher cannot prove is reported as a match. Concretely: a token spelled absolutely (/home/u/repo/notes/x.md) matches touches(["notes"]) whether or not a project root is available, and a token in a sibling checkout matches too, because a repo-relative prefix cannot rule it out. Prefix spelling is forgiving in the same direction — "notes", "notes/" and "notes/**" all name the same directory.

  Bounded, though: the prefix's path segments must actually occur in the token, so ordinary commands stay untouched. Two cases still miss, and both belong to the parser rather than the matcher — cd notes && cat x.md (a leaf's argument is not resolved against a preceding cd), and an absolute prefix against a relative token when no root is available at all.

  Until 2026-08-12 this bias did not exist: touches compared a repo-relative prefix against a raw token with no root anywhere in decideProgram, so spelling a path absolutely walked straight past any gate written with a relative prefix. Measured against a real shipped guard, sed -i s/a/b/ <abs>/paper.tex and cp /tmp/a <abs>/paper.tex both exited 0 while their relative spellings exited 2.

• e.path (Edit/Write) — a PathView with under(prefixes) for path confinement, plus raw (the path as the tool sent it) and rel (the same path repo-relative, or undefined — see below).

  Write your prefixes repo-relative; the runtime handles the rest. Claude Code's Edit/Write/MultiEdit tools send an absolute file_path, so under(["src"]) has to reconcile the two. It does that with the project root — $CLAUDE_PROJECT_DIR, else the event's own cwd, never the hook process's working directory (under a git worktree that can be a different checkout). An absolute prefix (under(["/etc"])) is matched against the absolute path instead, so both spellings work.

  under is the allowlist / coverage primitive, and an unprovable answer is false: a path in another checkout, or an absolute path with no root in sight, matches no repo-relative prefix. A confinement gate (under(ok) ? allow() : deny()) therefore fails closed, and a nudge stays quiet. The reverse shape — under(secret) ? deny() : allow() — reads that false as allow, so do not build a denylist on it. When there is genuinely no root, the runtime says so on stderr rather than deciding silently.

  Testing a file hook? Build the event with fileToolEvents(path) (from vigiles), which returns both spellings. Hand-written relative events are what let three shipped hooks stay dead while their tests passed.

• e.prompt (UserPromptSubmit) — the user's prompt text (a plain string).

• e.stopHookActive (Stop) — the loop guard; allow() when it's true.

• e.response (PostToolUse react) — a ResponseView: isError() (the tool failed) and contains(needle).

• allow() / deny(reason) / ask(reason) — the gate decision (every gate role).

• inject(text) — inject output. run(cmd) / notice(msg) / nothing() — react output.

• state(name) in needs, record(name, value?) in a return — runtime-owned named memory, so a hook can remember a fact without reaching for the filesystem. See below.

Remembering a fact — state() and record()

A hook that should speak at most once an hour, or only after something else actually happened, has to remember something. By hand that means a stamp file: a path, a format, and two hooks racing for the same one — and it means the hook can reach the filesystem at all, which is the capability compiling took away.

So the hook does not write. It declares a fact, and the runtime writes it:

export default experimental_defineHook({
  on: "Stop",
  needs: { sync: state("calendar.synced") },
  react: (e) =>
    e.ctx.sync.olderThan("1h")
      ? run("./bin/remind.sh") // meanwhile whoever DID the sync returns
      : nothing(), //   record("calendar.synced")
});

A key is a name, not a path — the runtime decides where it lives, so two hooks cannot disagree about a file. Reading one gives a StateFact:

field	meaning
recorded	has this key ever been written — the only way to tell "never" from "long ago"
value	the recorded string ("" when never)
at	ISO-8601 instant ("" when never)
ageSeconds	seconds since — Infinity when never recorded, never null
fresherThan(within) / olderThan(within)	"90s", "30m", "1h", "7d"

🔴 Infinity rather than null is a safety property, not a style choice. The natural throttle is if (ageSeconds < LIMIT) return nothing(). In JavaScript null < 3600 is true, so a key that was never recorded would read as fresh, and a newly installed hook would go silent forever — quietest exactly when it was just added. With Infinity every "younger than X" test is false on a missing key, so the hook fires. An unparseable timestamp is treated the same way, as never-recorded: that fails toward noise instead of toward a silence nobody can notice.

Throttling is not a separate feature — it is this one, read as "when did I last speak". And record is a declaration in the return value, not a call the hook makes, so a hook cannot record that something happened while doing nothing: the two cannot drift apart.

A prompt gate and a stop gate read like any other gate — they just decide over a different event:

import { experimental_definePromptGate, deny, allow } from "vigiles/hook";

// Refuse a prompt that looks like it's pasting a secret key.
export default experimental_definePromptGate({
  on: "UserPromptSubmit",
  decide: (e) =>
    /sk-[a-z0-9]{20}/i.test(e.prompt)
      ? deny("your prompt looks like it contains a secret key")
      : allow(),
});

import { experimental_defineStopGate, deny, allow } from "vigiles/hook";

// Don't let the agent stop while the tests are red.
export default experimental_defineStopGate({
  on: "Stop",
  decide: (e) =>
    e.stopHookActive // a prior block already fired — let it stop now (loop guard)
      ? allow()
      : deny("keep going until `npm test` passes"),
});

Observe mode (shadow rollout)

Switching a new gate straight to blocking is risky. What if it's too aggressive and stops work you wanted? Every gate takes a mode:

• enforce (default) — block on deny.
• observe — the shadow / rollout mode: compute the same decision, record what it would have blocked, and let everything through. Watch the log, confirm it only flags the bad stuff, then promote to enforce.

export default experimental_defineHook({
  on: "PreToolUse",
  match: tool("Bash"),
  mode: "observe", // ← shadow: record, don't block
  decide: (e) =>
    e.command.runs("git push", { force: true })
      ? deny("force-push to a protected branch")
      : allow(),
});

In observe mode the runtime exits 0 (never blocks) and appends a record to .vigiles/hook-observations.jsonl ({ ts, hook, event, would, reason }) plus a one-line ⚠ [vigiles observe] note. It's harness-neutral — exit 0 + a local record behaves identically on Claude Code and Codex, no harness-specific field names involved.

Deciding on external state (context providers)

A pure gate can only see the command/path/prompt/response. But a real guard often needs external state to decide — "is this a push to main?", "is the tree dirty?". A hand-written hook would shell out ($(git branch --show-current)); a compiled hook can't do I/O (that's the capability guarantee).

The fix is the same one Cedar/OPA/Gatekeeper use: the hook never fetches — it declares what it needs, and the trusted runtime gathers those read-only facts and hands them in as e.ctx.

import { experimental_defineHook, tool, deny, allow } from "vigiles/hook";

export default experimental_defineHook({
  on: "PreToolUse",
  match: tool("Bash"),
  needs: ["git.branch"], //                ← declared; gathered by the runtime
  decide: (e) =>
    e.ctx["git.branch"] === "main" && e.command.runs("git push")
      ? deny("no direct pushes to main")
      : allow(),
});

The guarantee is intact and stronger: the hook still does zero I/O. The runtime runs git branch --show-current (provably read-only) and injects the result. needs is typed — reading an undeclared fact (e.ctx["cwd"] here) is a tsc error, and an unknown provider name won't compile — so the capability surface stays explicit and auditable.

Built-in providers: git.branch, git.isDirty, git.root, cwd, os.platform, env.isCI — zero-arg, read-only. A provider that can't resolve (e.g. not a git repo) yields its default, never an error. The set is deliberately small. A 20+ OSS survey found most facts a hook reads are already event data, and the long tail belongs in the opt-out, not a growing catalog. (env.isCI uses the ci-info library — the one fact where a maintained lib beat hand-rolling. Git facts stay read-only shell commands; platform is process.platform.)

The lightweight opt-out — provide / dangerously. For a one-off, off-catalog fact you don't want to register a whole provider for, declare an inline command right in needs:

import {
  experimental_defineHook,
  tool,
  deny,
  allow,
  provide,
} from "vigiles/hook";

export default experimental_defineHook({
  on: "PreToolUse",
  match: tool("Bash"),
  needs: [provide("k8sCtx", "kubectl config current-context")], // read-only, inline
  decide: (e) =>
    e.ctx.k8sCtx === "prod" && e.command.runs("kubectl delete")
      ? deny("no kubectl delete against prod")
      : allow(),
});

The trusted runtime runs the command (so decide still does zero I/O) and hands its stdout in as e.ctx[name]. provide(name, cmd) requires a provably read-only command (compile rejects it otherwise). dangerously(name, cmd) is the loud, greppable escape for a command that isn't — the dangerouslySetInnerHTML / unsafe convention, so a security review can search for that one word.

Reusable registered providers. For a fact several hooks share, register it once in .vigiles/providers/<name>.{mjs,ts} and reference it by name:

// .vigiles/providers/k8sCtx.mjs
import { defineProvider } from "vigiles/hook";
export default defineProvider({
  name: "k8sCtx",
  run: "kubectl config current-context",
});

// any hook:  needs: [provider("k8sCtx")]  →  e.ctx.k8sCtx

vigiles compile validates each provider is read-only (or dangerous: true) and that every provider() ref resolves to a registered file.

The opt-out ladder (you're never trapped): built-in providers → inline provide / dangerously → registered defineProvider (reusable, named) → the shell lane (a hand-written .sh for arbitrary in-decision logic, verified with the disaster battery). You always know which rung you're on.

Compile and wire

Put your hook source in .vigiles/hooks/. The typed program is harness-neutral — it imports vigiles/hook and compiles to whichever harness you target — so it lives in vigiles's own dir, not a harness's .claude/. Then:

npx vigiles compile                                  # discovers .vigiles/hooks/* (and your specs)
npx vigiles compile .vigiles/hooks/safe-bash-guard.mjs   # …or target one file

There is no separate compile-hook verb — compiling a typed authoring artifact into the harness's native format is one verb, whatever the artifact (a .spec.ts → markdown, a hook → a wired config). compile:

1. Runs the capability check (an out-of-vocabulary import fails the build).
2. Merges the hook block into the active harness's config — .claude/settings.json (JSON) or .codex/config.toml (TOML) — idempotently, keyed by the hook path. Recompiling updates in place and never clobbers your own hand-written hooks.
3. Writes a tamper-evident stamp beside the source.

The merged block routes the live event to vigiles hook-runtime run-program <file>:

// .claude/settings.json — written (not pasted) by `vigiles compile`
{
  "hooks": {
    "PreToolUse": [
      {
        "matcher": "Bash",
        "hooks": [
          {
            "type": "command",
            "command": "npx vigiles hook-runtime run-program .vigiles/hooks/safe-bash-guard.mjs",
          },
        ],
      },
    ],
  },
}

hook-runtime run-program is a hidden runtime entrypoint — invoked by the harness on every matching event, never typed by hand. It loads your typed program, verifies the stamp (a hand-edited artifact is refused — fail closed), and dispatches by role: a gate exit 2s on deny, an inject prints additionalContext, a react runs its classified command. You wrote none of that protocol. (compile is the one-time wiring step; hook-runtime is the per-event executor the wiring points at — see the CLI surface for why they're distinct.)

Hooks can be authored in JavaScript (.mjs) or TypeScript (run under tsx / Node ≥ 23.6). vigiles/hook is the only import a compiled hook may use.

Multi-harness. The typed program is harness-neutral; only the merged config differs. vigiles compile --harness=codex merges a Codex config.toml [[hooks.<event>]] block (an anchored-regex matcher) instead of Claude Code's settings.json JSON. A repo that declares both harnesses (harness: ["claude-code", "codex"] in .vigilesrc.json) gets the SAME hook installed into both configs — vigiles compile (no flag) fans out to every declared harness, so a hook is never silently wired on one and missing on the other. The gate runtime is shared, since Codex vetoes a tool call via exit 2 exactly as Claude Code does. Inject output (additionalContext) is confirmed shared with Codex too, so an inject hook compiles for both — compile --harness=codex only warns if you target an event that harness doesn't honor for injection (each harness declares its injectableEvents). React output is the one piece still Claude-Code-confirmed only, so compile --harness=codex warns loudly on a react hook rather than ship a maybe-no-op.

Where things live

Everything is committed, and the source is adapter-agnostic — one hook compiles to any harness you target:

Artifact	Location	Why
Hook source	.vigiles/hooks/*.{mjs,ts}	harness-neutral — one source, fans out to any harness
Provider source	.vigiles/providers/*.{mjs,ts}	registered context providers (defineProvider), referenced by name
Tamper stamp	.vigiles/hooks/<name>.json	the runtime verifies it before running the hook
Wiring	.claude/settings.json / .codex/config.toml	compile merges it in per harness (a multi-harness repo gets both)

Hooks are not auto-discovered by sitting just anywhere — they must be under .vigiles/hooks/ (or named explicitly to compile). Because they share one dir, basenames are unique, so the stamp keys safely on the basename.

Editing a compiled hook (the stamp, and the way out)

The stamp makes the runtime refuse a hook whose source no longer matches what was compiled. That's the point — but it also applies while you are editing the hook, and a stale PreToolUse Bash gate blocks every Bash command, vigiles compile included. That would wedge the repo: you couldn't recompile, because the stale gate refused to let you.

The way out is a file write, not a command. A Bash gate never gated file tools, so both of these work while every command is refused:

• edit the hook's source back to what was compiled; or
• clear its stamp — write {} into .vigiles/hooks/<name>.json (or delete it). The hook then loads and runs unstamped, and — this is the part that matters — it goes back to enforcing. You are not disarming the gate, you are un-sticking it. Then recompile through the normal gate:

npx vigiles compile .vigiles/hooks/guard.mjs

The refusal prints the exact sidecar path, so you don't have to work it out:

vigiles: hook guard.mjs does not match its compiled stamp (tampered).
vigiles: if YOU edited it, the way out is a FILE WRITE, not a command — this
  refusal blocks the recompile too. Either edit guard.mjs back to what was
  compiled, or clear its stamp by writing `{}` into
  /repo/.vigiles/hooks/guard.mjs.json. The hook then runs UNSTAMPED but still
  ENFORCES, so `vigiles compile guard.mjs` goes through the normal gate.

If a hook stops loading entirely (a conflicted package.json so Node can't resolve vigiles/hook, a typo mid-edit), the same fail-closed refusal applies — and the way out is again a file write. Writes to the hook's own source, its stamp sidecar, or package.json / .vigilesrc.json are allowed while every command is refused. That set is complete rather than a guess: a compiled hook may import nothing but vigiles/hook, so its load path is the hook file plus the config that resolves that specifier. Fix whichever is broken and the hook loads again; the gate then decides normally, and git merge --abort is an ordinary allowed command — through the gate rather than around it.

A write, under a tool that writes. The escape admits Write, Edit and MultiEdit — the tools measured to write a file and carry file_path. A Read of the same path is refused: a read repairs nothing, and while the wedged hook is registered for Read it would otherwise walk straight out through the escape. An unrecognised tool name is refused as well; the list does not need to be complete, only non-empty, because a new writing tool wedges nothing — you still repair with Write. (NotebookEdit is absent on purpose: it writes, but its input field is notebook_path, so it never carries the path this door reads.)

In this repository only. The allowed write is the file the runtime itself derived, not a path that merely ends the same way: both the event's path and the runtime's are resolved against the project root before they are compared, so /repo/package.json and package.json are the same file while /home/another-project/package.json is refused. That path could not repair the failure anyway, and a wedge in one checkout has no business handing out a write in another. Node walks the package.json chain upward, so a monorepo package's own package.json is on the list; a sibling directory's is not.

Why no command is allowed, including git. git merge --abort, git rebase --abort and git checkout -- <path> used to be, on the reasoning that they only move the tree to states git already holds and execute no repo code. Measured against git 2.43.0 with hooks installed in .git/hooks/, that is false for all three: git checkout -- <path> runs post-checkout, and both aborts run reference-transaction (it fires on any ref update, which each of them performs). .git/hooks/* is writable by exactly the actor this door assumes, so the whitelist was an arbitrary-execution path standing open precisely while the gate enforced nothing — the same mistake as the vigiles compile escape, one layer down: a command believed inert because of what it means rather than what it does. git -c core.hooksPath=<empty> does suppress them (measured), but it puts free-form structure back into the accepted string and buys nothing, because a file write already un-wedges the repo.

Why vigiles compile is not in that list. It used to be. Two things settled it, both measured rather than argued. During a load wedge vigiles compile exits 1 (Cannot load hook …: Invalid package config) — it loads the hook through the very resolver that just failed, so it could never repair that state. And it was the only escape that ran code: over five review rounds it was found to admit a payload through composition (curl … | sh && vigiles compile), through its operand (vigiles compile /tmp/payload.spec.ts, which the CLI dynamically imports), through its executable path (/tmp/vigiles compile), and through the working directory (cd /tmp/evil && vigiles compile). Recognising a trusted action from an untrusted string has unbounded degrees of freedom — argv, cwd, PATH, node_modules resolution, config discovery — so the primitive was removed rather than constrained a fifth time.

Everything else still fails closed. This doesn't soften the tamper guarantee that matters: while the stamp is stale the hook is enforcing nothing (it refuses every call), and anyone able to rewrite a hook's source can equally rewrite .claude/settings.json. What the stamp buys is that a smuggled capability can never run silently — unchanged.

Testing a compiled hook

Because the decision is a pure function, you test it deterministically — no model, and (cheapest) no subprocess. Three levels, by cost:

1. In-process (cheapest). Load the hook FILE with loadHook(path) and pass it plus a raw event to the assertions — no node spawn, no CLI, milliseconds:

import { it } from "vitest";
import { loadHook, assertHookDenies, assertHookAllows } from "vigiles";

const guard = await loadHook(".vigiles/hooks/guard.mjs");

it("blocks a force-push, even hidden in a compound command", () => {
  assertHookDenies(guard, {
    tool_name: "Bash",
    tool_input: { command: "cd x && git push -f" },
  });
  assertHookAllows(guard, {
    tool_name: "Bash",
    tool_input: { command: "git status" },
  });
});

loadHook is the same loader the runtime uses (so a hook that loads in a test loads identically in production) and it is what makes this tier reachable from a .harness.mjs file, which has a hook's PATH and not its object. A TypeScript hook (guard.hook.ts) loads the same way under tsx / Node ≥ 23.6. If you already have the object — a static import guard from "./guard.mjs" — pass it directly.

React hooks get their own pair. A react can't block, so the gate assertions don't apply; use assertHookNotices(hook, event, matcher?) and assertHookSilent(hook, event):

import { assertHookNotices, assertHookSilent } from "vigiles";

const warn = await loadHook(".vigiles/hooks/warn-on-failure.mjs");
const after = (isError) => ({
  tool_name: "Bash",
  tool_input: { command: "npm test" },
  tool_response: isError ? { error: "boom" } : { stdout: "ok" },
});

assertHookNotices(warn, after(true), /read the error/);
assertHookSilent(warn, after(false));

⚠️ Don't test a react hook by reading stdout. notice(…) writes to stderr, so a probe built on execFileSync (which returns stdout only) sees nothing and reports a perfectly healthy react hook as dead. These assertions read the reaction itself, so the stream never enters into it.

Runnable end to end: examples/harness/compiled-hook-inprocess.harness.mjs (with its two hook files) is exactly this pattern, and runs in CI.

runHookProgram(hook, event) is the underlying primitive — it returns a normalized outcome ({ kind: "decision" | "injection" | "reaction", … }) dispatched by role, so an inject or react hook is just as testable as a gate.

2. Through the real runtime. runHook("node … hook-runtime run-program guard.mjs", event) drives the actual compiled CLI (stamp check + dispatch) — proves the wired artifact behaves, still no model. Pair it with the disaster battery: assertBlocksDisasters("node … hook-runtime run-program guard.mjs") proves the gate blocks every textbook disaster.

3. Does it fire in the assembled harness? runHarnessTest (a scripted mock model emits the tool call; assert the hook blocked) — the delivery question, key-free, and capped by the delivery floor.

See Testing your harness for the tiers in full.

Proof: the OSS dogfood

We pointed the DISASTER_CATALOG battery (force-push, compound force-push, reset --hard, rm -rf, --no-verify, private-SSH-key read, curl | sh) at the widely-copied disler/claude-code-hooks-mastery safety hook: it blocks 2 of 7, silently missing the other five. The compiled equivalent (examples/harness/safe-bash-guard.mjs) blocks 7 of 7 by construction — same intent, no blind spots, no protocol bug. The contrast is a runnable, model-free regression test (src/hook-dogfood.test.ts).

Beyond the headline number, the structural wins over hand-written guards — each isolated in CI (src/hook-oss-comparison.test.ts) so it's non-circular — are:

• Evasion — the AST catches the compound cd … && git push -f a substring/glob misses.
• Precision — no grep false-positive on a benign echo.
• Protocol — a mis-wired exit 1 is false confidence; the compiled exit code can't be wrong.

The honest other side: stateful guards, broad I/O, and delivery (#34692) are NOT compiled-hook wins.

Limitations & trade-offs (the cons)

Compiled hooks are neither free nor magic. The honest downsides:

• ❌ Delivery floor — a gate is a strong default, not an unbypassable wall. Compiling fixes a hook's authoring and logic, not how the harness delivers events to it.

  What changed (2026-08-24). Claude Code's #34692 — a PreToolUse hook not firing for a subagent's tool calls — was closed not-planned and quoted here for months as a standing limit. It is fixed: measured against a stock @anthropic-ai/claude-code@2.1.241 from the registry, a subagent's own Bash reaches the hook and an exit-2 deny stops it (the parent's identical command in the same run is the control). The event even carries agent_type, naming which subagent made the call. src/subagent-delivery.test.ts pins this in both directions, so a regression goes red instead of quietly returning to the old behaviour.

  What did NOT change. A model can still route around a tool entirely (#45427 / #32376 — a Bash heredoc instead of Write), and a compiled hook removes the bugs that are yours, not the harness's. The most robust claim remains about logic, not live enforcement, and guardrail verification is still the companion that survives any delivery gap. Never call a gate "unbypassable."

  Scope of the measurement, stated plainly: it drives claude -p (headless). Interactive sessions are unmeasured, and subagent nesting (depth 2) does not occur there at all.

• ⚠️ Runtime cost. Every matching event spawns node and dynamic-imports your program — tens to hundreds of ms per call. Fine for a PreToolUse gate. Think twice before a hot-path PostToolUse react that fires on every edit.

• ⚠️ Buy-in. It's a dependency plus a build step, and you author in JS/TS, not a 3-line inline bash hook. For a trivial one-liner the compiled path is heavier — the payoff is on the guards that actually have to be correct.

• ⚠️ A bounded vocabulary is a ceiling, by design — but be precise about which bound. (1) What a hook can do: checkHookImports forbids any import but vigiles/hook (no fs/net/child_process), so a hook that must call a service, read a file, or hold cross-invocation state to decide can't be expressed. That is the deliberate ceiling — it is the safety guarantee, and such hooks stay hand-written (keep a plain shell hook and verify it with the disaster battery). (2) What a hook can see: the AST matchers (runs/touches/pipesToShell/under) are a soft, extensible limit, not a fundamental one — if you need to match a shape they don't expose yet, the fix is a new matcher, not a redesign.

• ⚠️ Compiling proves the protocol, not your policy. A compiled hook can't have the wrong exit code — but it can still deny the wrong thing. Compiling is necessary, not sufficient. Test the logic with guardrail verification.

• ℹ️ Codex inject/ask output is unconfirmed. The gate (deny → exit 2) path is cross-harness today. An inject/react hook's output shape is Claude-Code-confirmed only, so compile --harness=codex warns loudly on those rather than ship a maybe-no-op (see Compile and wire).

Status / pending

The vocabulary's six entry points carry the experimental_ prefix. This section says what that prefix is claiming and what would retire it — the roadmap for the feature lives with the feature, not on a separate stability page.

They are experimental_defineHook, experimental_defineFileGate, experimental_definePromptGate, experimental_defineStopGate, experimental_defineInject and experimental_defineReact — everything this page has been about.

Only the entry points carry the prefix, and that placement is the whole point: every other name in vigiles/hook — allow, deny, tool, pathView, commandView, state, record, notice, run — is reachable ONLY from inside a define* call. Prefixing the chokepoint makes the marking structural for the whole vocabulary; prefixing thirty names could not, because nothing would stop the thirty-first from shipping unmarked. Same reasoning as experimental_skill.input() (see skills.md), applied to a larger surface.

Why it is not settled, stated as gaps rather than as a disclaimer:

• The vocabulary grew a whole new axis in one release. Runtime-owned named state (record/state) landed 2026-08-12 to close a measured hole — seven advisory hooks in the dogfood repo were still hand-written shell for one uniform reason, every one of them both read and wrote a stamp file, and throttling was inexpressible. An API that gained a dimension that recently has not been pressure-tested by anyone but its author.
• 🔴 Testing a hook that uses named state is archaeology today. The runtime derives the store's path from the hook's own location and validates the key charset, so a test that wants to seed "this fact was recorded four days ago" must reconstruct a private path. The dogfood repo does exactly that, hard-coded, and it broke when the facts were renamed. There is no supported seeding API beside runHook. Until there is, a consumer testing a throttle is depending on internals.
• vigiles compile is not idempotent — it appends a duplicate wiring block that has to be removed by hand.
• Two consumers total, both belonging to the author.

What would have to be true to drop the prefix: a supported way to seed and read named state in a test; an idempotent compile; and at least one consumer who did not write the API.

Stable alternative: a hand-written shell hook wired in settings.json. The events and the protocol are the harness's, not ours — nothing about them is experimental. What you give up is the typed vocabulary and everything it makes unrepresentable.

See also

• Testing your harness — the test tiers; runHook unit-tests a hook's decision, and assertBlocksDisasters proves a guardrail blocks.
• Verifying your instruction files — the linting layer (references are true); compiled hooks are the gate instrument beside it.
• CLI & GitHub Action — compile / hook-runtime reference.
• API reference (generated) — every vigiles/hook symbol (experimental_defineHook, provide/dangerously/defineProvider, the Decision/Reaction types, …).