diff --git a/engine/src/hooks.claude-stop.test.ts b/engine/src/hooks.claude-stop.test.ts
new file mode 100644
index 00000000..1391ed2d
--- /dev/null
+++ b/engine/src/hooks.claude-stop.test.ts
@@ -0,0 +1,192 @@
+import { afterAll, beforeAll, expect, test } from 'bun:test';
+import fs from 'node:fs/promises';
+import os from 'node:os';
+import path from 'node:path';
+import { fileURLToPath } from 'node:url';
+
+/**
+ * The Stop hook SCRIPT, executed as Claude Code executes it.
+ *
+ * Everything else about this feature was covered and this was not: the CLI verb
+ * (`kild inbox --format claude-stop`) has tests, and the shell wrapper that decides what to
+ * pass it had none. Nothing ran the file. It reads `session_id` off stdin with `sed`, gates
+ * on `set -eu`, and chooses whether to pass `--session`/`--as` — none of which the TypeScript
+ * tests touch, because they invoke the CLI directly.
+ *
+ * That gap is the shape of the thing: **verification code is exempted from gates because it
+ * is not product, and the exemption is what lets it rot.** This script's own header warns
+ * that a renamed verb "does not raise an error, it just stops working" — and the previous
+ * generation of it did exactly that, silently, for months. It warned about itself while
+ * nothing checked it.
+ *
+ * The contract, in one line, and every case here asserts it: print the drain's JSON, or print
+ * NOTHING, and ALWAYS exit 0. A hook that cannot reach kild must never stop a turn.
+ */
+
+const HOOK = path.join(
+  path.dirname(fileURLToPath(import.meta.url)),
+  '..',
+  '..',
+  'hooks',
+  'claude-stop',
+);
+const CLI = path.join(path.dirname(fileURLToPath(import.meta.url)), 'cli.ts');
+
+let engine: ReturnType<typeof Bun.serve> | undefined;
+let engineUrl = '';
+let kildHome = '';
+let binDir = '';
+/** What the stub answers a drain with. */
+let drain: { messages: Array<{ from: string; text: string; ts: number }> } = { messages: [] };
+
+beforeAll(async () => {
+  kildHome = await fs.realpath(await fs.mkdtemp(path.join(os.tmpdir(), 'kild-hook-home-')));
+  binDir = await fs.realpath(await fs.mkdtemp(path.join(os.tmpdir(), 'kild-hook-bin-')));
+
+  engine = Bun.serve({
+    port: 0,
+    hostname: '127.0.0.1',
+    fetch: () =>
+      Response.json({ ok: true, idle: drain.messages.length === 0, capped: false, ...drain }),
+  });
+  engineUrl = `http://127.0.0.1:${engine.port}`;
+
+  // The hook finds `kild` on PATH. Give it a real one that runs this checkout's CLI, so the
+  // test exercises the actual wiring rather than a mock of it.
+  const shim = path.join(binDir, 'kild');
+  await fs.writeFile(shim, `#!/bin/sh\nexec bun run ${CLI} "$@"\n`);
+  await fs.chmod(shim, 0o755);
+});
+
+afterAll(async () => {
+  engine?.stop(true);
+  await fs.rm(kildHome, { recursive: true, force: true });
+  await fs.rm(binDir, { recursive: true, force: true });
+});
+
+/** Run the hook exactly as Claude Code does: payload on stdin, environment, nothing else. */
+async function runHook(
+  payload: unknown,
+  env: Record<string, string> = {},
+  opts: { onPath?: boolean } = {},
+) {
+  const proc = Bun.spawn(['sh', HOOK], {
+    env: {
+      PATH: `${opts.onPath === false ? '' : `${binDir}:`}${process.env.PATH ?? ''}`,
+      HOME: process.env.HOME ?? '',
+      KILD_ENGINE: engineUrl,
+      KILD_HOME: kildHome,
+      ...env,
+    },
+    stdin: new TextEncoder().encode(JSON.stringify(payload)),
+    stdout: 'pipe',
+    stderr: 'pipe',
+  });
+  const [stdout, stderr, exitCode] = await Promise.all([
+    new Response(proc.stdout).text(),
+    new Response(proc.stderr).text(),
+    proc.exited,
+  ]);
+  return { stdout, stderr, exitCode };
+}
+
+/** Attach a session so the hook has a record to resolve, using the real CLI. */
+async function attach(session: string, kildId: string, handle: string) {
+  const proc = Bun.spawn(['bun', 'run', CLI, 'attach', kildId, '--as', handle], {
+    env: {
+      ...process.env,
+      KILD_ENGINE: engineUrl,
+      KILD_HOME: kildHome,
+      CLAUDE_CODE_SESSION_ID: session,
+    },
+    stdout: 'pipe',
+    stderr: 'pipe',
+  });
+  await proc.exited;
+}
+
+test('with mail waiting, the hook prints Stop JSON and exits 0', async () => {
+  await attach('sess-hook-1', 'kild-h', 'claude');
+  drain = { messages: [{ from: 'reviewer', text: 'PR is green', ts: 1 }] };
+
+  const hook = await runHook({ session_id: 'sess-hook-1', hook_event_name: 'Stop' });
+  expect(hook.exitCode).toBe(0);
+  expect(JSON.parse(hook.stdout)).toMatchObject({
+    decision: 'block',
+    hookSpecificOutput: { hookEventName: 'Stop' },
+  });
+  drain = { messages: [] };
+});
+
+test('the session id is read from the PAYLOAD when the environment has none', async () => {
+  // The whole reason the hook stopped discarding stdin. `--resume`/`--fork-session` mints a
+  // new session id and a harness settings file can re-inject a stale kild id, so the payload
+  // is the only channel that survives either.
+  await attach('sess-hook-payload', 'kild-h', 'claude');
+  drain = { messages: [{ from: 'agent', text: 'x', ts: 1 }] };
+
+  const hook = await runHook({ session_id: 'sess-hook-payload' });
+  expect(hook.exitCode).toBe(0);
+  expect(hook.stdout).toContain('@agent');
+  drain = { messages: [] };
+});
+
+test('with no mail, the hook prints NOTHING and exits 0', async () => {
+  await attach('sess-hook-2', 'kild-h', 'claude');
+  const hook = await runHook({ session_id: 'sess-hook-2' });
+  expect(hook.stdout).toBe('');
+  expect(hook.exitCode).toBe(0);
+});
+
+test('a session that never attached is silent, not an error', async () => {
+  const hook = await runHook({ session_id: 'sess-never-attached' });
+  expect(hook.stdout).toBe('');
+  expect(hook.exitCode).toBe(0);
+});
+
+test('no session id anywhere: the hook does nothing at all, fast', async () => {
+  const hook = await runHook({ hook_event_name: 'Stop' });
+  expect(hook.stdout).toBe('');
+  expect(hook.exitCode).toBe(0);
+});
+
+test('a DEAD engine is silence and exit 0 — never a blocked turn', async () => {
+  await attach('sess-hook-dead', 'kild-h', 'claude');
+  const hook = await runHook(
+    { session_id: 'sess-hook-dead' },
+    { KILD_ENGINE: 'http://127.0.0.1:1' },
+  );
+  expect(hook.stdout).toBe('');
+  expect(hook.exitCode).toBe(0);
+});
+
+test('no kild on PATH is silence and exit 0', async () => {
+  // A stale wiring on another machine must not fail somebody's every turn. A real PATH with
+  // no kild on it — not an empty one, which would also lose the shell.
+  const hook = await runHook({ session_id: 'sess-hook-1' }, { PATH: '/usr/bin:/bin' });
+  expect(hook.stdout).toBe('');
+  expect(hook.exitCode).toBe(0);
+});
+
+test('malformed JSON on stdin is silence and exit 0', async () => {
+  const proc = Bun.spawn(['sh', HOOK], {
+    env: {
+      PATH: `${binDir}:${process.env.PATH ?? ''}`,
+      KILD_ENGINE: engineUrl,
+      KILD_HOME: kildHome,
+    },
+    stdin: new TextEncoder().encode('{not json at all'),
+    stdout: 'pipe',
+    stderr: 'pipe',
+  });
+  const [stdout, exitCode] = await Promise.all([new Response(proc.stdout).text(), proc.exited]);
+  expect(stdout).toBe('');
+  expect(exitCode).toBe(0);
+});
+
+test('the hook never writes to stdout except the block JSON', async () => {
+  // stray chatter on a hook reads as a failure to the harness.
+  await attach('sess-hook-quiet', 'kild-h', 'claude');
+  const hook = await runHook({ session_id: 'sess-hook-quiet' });
+  expect(hook.stdout).toBe('');
+});