diff --git a/.gitea/workflows/ci.yml b/.gitea/workflows/ci.yml
index 77e8bcc..22652f1 100644
--- a/.gitea/workflows/ci.yml
+++ b/.gitea/workflows/ci.yml
@@ -77,6 +77,32 @@ jobs:
       - name: Run migration ledger test suite
         run: node --test tests/database-postgres-ledger.test.mjs
 
+  # E00-S03-T04: the static assertions of tests/database-postgres-lock.test.mjs
+  # gate every PR — the suite locks in the migration advisory lock (session-
+  # scoped pg_advisory_lock/pg_try_advisory_lock over a stable keyed hash on a
+  # dedicated connection, driver-boundary re-export) with mutation probes, and
+  # the docker-gated real-stack concurrent probe (a second runner waits or
+  # fails while the first holds the lock; the lock releases when the holding
+  # session ends) runs where a Docker daemon is available and skips cleanly
+  # otherwise. The job installs the frozen workspace because the real-stack
+  # probe executes the committed lock module from the host (it imports `pg`
+  # through the package's own links).
+  database-postgres-lock:
+    name: Migration advisory lock (E00-S03-T04)
+    runs-on: ubuntu-latest
+    steps:
+      - uses: actions/checkout@v4
+      - name: Install Node.js 24
+        uses: actions/setup-node@v4
+        with:
+          node-version: '24'
+      - name: Enable pnpm (corepack, pinned to 11.23.0 via packageManager)
+        run: corepack enable
+      - name: Install dependencies (frozen lockfile)
+        run: pnpm install --frozen-lockfile
+      - name: Run migration advisory lock test suite
+        run: node --test tests/database-postgres-lock.test.mjs
+
   # E00-S03-T01: the static assertions of tests/compose-config.test.mjs (db
   # image pinned to postgres:18.6-bookworm, health gate, volume persistence,
   # build platforms) gate every PR (the docker-gated real-stack probes inside
diff --git a/tests/database-postgres-lock.test.mjs b/tests/database-postgres-lock.test.mjs
new file mode 100644
index 0000000..8170a7b
--- /dev/null
+++ b/tests/database-postgres-lock.test.mjs
@@ -0,0 +1,536 @@
+/**
+ * Migration advisory lock test — locks in the [E00-S03-T04] advisory lock
+ * that prevents concurrent migration runners.
+ *
+ * Acceptance criteria covered (each test fails without the committed state):
+ *   - "advisory lock prevents concurrent migration runners" → the committed
+ *     `packages/database-postgres/src/lock.ts` defines a `MigrationLock`
+ *     backed by PostgreSQL session-scoped advisory locks keyed by a stable
+ *     constant (`MIGRATION_LOCK_KEY` → `hashtextextended($1, 0)`): `acquire()`
+ *     blocks (`pg_advisory_lock`) and `tryAcquire()` fails fast
+ *     (`pg_try_advisory_lock`), both on a dedicated pool connection; the
+ *     docker-gated real-stack probe starts a real database and proves two
+ *     runners cannot hold the lock at once (the issue's test plan: "run a
+ *     concurrent migration lock test").
+ *   - "a second runner waits or fails while the first holds the lock" → the
+ *     real-stack probe holds the lock in the first runner, shows the second
+ *     runner's `tryAcquire()` returns false (fails fast) and its blocking
+ *     `acquire()` waits (the server reports `wait_event advisory` for the
+ *     waiting session) until the first runner releases, then acquires; a
+ *     session that takes the lock and then closes (the runner exits)
+ *     releases it — the issue's rollback note ("the lock releases when the
+ *     runner exits").
+ *   - the lock is part of the driver boundary: `src/index.ts` re-exports
+ *     `MigrationLock` + `MIGRATION_LOCK_KEY`, so no other package needs the
+ *     `pg` driver to lock migration state.
+ *
+ * Run: `node --test tests/database-postgres-lock.test.mjs`
+ * (node:test — built into Node >= 18; no dependencies, lockfile untouched.)
+ */
+
+import test from 'node:test';
+import assert from 'node:assert/strict';
+import { readFileSync, existsSync, writeFileSync, rmSync } from 'node:fs';
+import { spawnSync } from 'node:child_process';
+import path from 'node:path';
+import { fileURLToPath } from 'node:url';
+
+const REPO_ROOT = path.resolve(path.dirname(fileURLToPath(import.meta.url)), '..');
+
+const read = (relPath) => readFileSync(path.join(REPO_ROOT, relPath), 'utf8');
+
+/** The committed advisory-lock module and the driver boundary that re-exports it. */
+const LOCK_SRC = 'packages/database-postgres/src/lock.ts';
+const INDEX_SRC = 'packages/database-postgres/src/index.ts';
+
+/** The root test glob (root `scripts.test`, E00-S01-T12) that runs every suite. */
+const ROOT_TEST_GLOB = 'tests/**/*.test.mjs';
+
+/** The CI job that gates the advisory-lock criterion on every PR. */
+const CI_JOB = 'database-postgres-lock';
+
+/** The committed advisory-lock key (stable namespace, bound as $1). */
+const LOCK_KEY = 'personal-blog-migrations';
+
+// ---------------------------------------------------------------------------
+// Static assertions on the committed lock source
+// ---------------------------------------------------------------------------
+
+/**
+ * Asserts the lock module exists with the documented shape: a `MigrationLock`
+ * class and a stable `MIGRATION_LOCK_KEY` constant. Fails fast on a missing
+ * module; the mutation probes below prove the assertions are non-vacuous.
+ */
+function assertLockModule(src) {
+  assert.match(src, /export class MigrationLock/, 'the lock module must export the MigrationLock class');
+  assert.match(
+    src,
+    /export const MIGRATION_LOCK_KEY = 'personal-blog-migrations'/,
+    'the lock module must declare the MIGRATION_LOCK_KEY constant',
+  );
+  assert.match(
+    src,
+    /get isHeld\(\)/,
+    'the lock module must expose isHeld so callers can tell whether the instance holds the lock',
+  );
+}
+
+/**
+ * Asserts the blocking path: `acquire()` takes a session-scoped advisory lock
+ * (`SELECT pg_advisory_lock(hashtextextended($1, 0))`) on a dedicated
+ * connection (`pool.connect()`), keyed by the stable constant bound as a
+ * parameter — a second runner calling `acquire()` waits while the first holds
+ * the lock. The key is never interpolated into the SQL.
+ */
+function assertBlockingAcquire(src) {
+  assert.match(
+    src,
+    /SELECT pg_advisory_lock\(hashtextextended\(\$1, 0\)\)/,
+    'acquire() must take the blocking session-scoped advisory lock (SELECT pg_advisory_lock(hashtextextended($1, 0)))',
+  );
+  assert.match(src, /pool\.connect\(\)/, 'the lock must be held on a dedicated connection (pool.connect())');
+  assert.match(src, /\[MIGRATION_LOCK_KEY\]/, 'the lock key must be passed as the bound-parameter array ([MIGRATION_LOCK_KEY])');
+  assert.doesNotMatch(
+    src,
+    /\$\{MIGRATION_LOCK_KEY\}/,
+    'the lock key must never be interpolated into the SQL',
+  );
+}
+
+/**
+ * Asserts the non-blocking path: `tryAcquire()` uses
+ * `SELECT pg_try_advisory_lock(hashtextextended($1, 0)) AS acquired` and
+ * resolves `false` when another runner holds the lock — a second runner fails
+ * fast while the first holds the lock.
+ */
+function assertNonBlockingAcquire(src) {
+  assert.match(
+    src,
+    /SELECT pg_try_advisory_lock\(hashtextextended\(\$1, 0\)\) AS acquired/,
+    'tryAcquire() must use the non-blocking advisory lock (SELECT pg_try_advisory_lock(hashtextextended($1, 0)) AS acquired)',
+  );
+  assert.match(src, /result\.rows\[0\]\?\.acquired === true/, 'tryAcquire() must resolve true only when the lock was acquired');
+  assert.match(src, /return false;/, 'tryAcquire() must resolve false when another runner holds the lock');
+}
+
+/**
+ * Asserts the session-scoped release: `release()` unlocks the holding session
+ * (`SELECT pg_advisory_unlock(hashtextextended($1, 0))`) BEFORE returning the
+ * connection to the pool (`client.release()`), so a pooled connection is
+ * never reused while still holding the lock; releasing an unheld instance is
+ * a no-op.
+ */
+function assertSessionScopedRelease(src) {
+  const releaseBody = src.slice(src.indexOf('async release()'));
+  assert.match(
+    releaseBody,
+    /SELECT pg_advisory_unlock\(hashtextextended\(\$1, 0\)\)/,
+    'release() must unlock the holding session (SELECT pg_advisory_unlock(hashtextextended($1, 0)))',
+  );
+  assert.match(releaseBody, /client\.release\(\)/, 'release() must return the connection to the pool (client.release())');
+  assert.ok(
+    releaseBody.indexOf('pg_advisory_unlock') < releaseBody.indexOf('client.release()'),
+    'release() must unlock the session before returning the connection to the pool',
+  );
+}
+
+/** Asserts the driver boundary re-exports the lock from the package entrypoint. */
+function assertBoundaryReexport(src) {
+  assert.match(
+    src,
+    /export \{ MigrationLock, MIGRATION_LOCK_KEY \} from '\.\/lock\.js'/,
+    'the driver boundary must re-export the lock (src/index.ts → ./lock.js)',
+  );
+}
+
+// ---------------------------------------------------------------------------
+// Docker probe helpers (integration test skips cleanly without Docker)
+// ---------------------------------------------------------------------------
+
+function run(cmd, args, opts = {}) {
+  return spawnSync(cmd, args, {
+    encoding: 'utf8',
+    timeout: 600_000,
+    ...opts,
+  });
+}
+
+/** True when the `docker` CLI with the Compose plugin is on PATH. */
+function dockerComposeAvailable() {
+  try {
+    return run('docker', ['compose', 'version'], { timeout: 15_000 }).status === 0;
+  } catch {
+    return false;
+  }
+}
+
+/** True when a reachable Docker daemon exists. */
+function dockerDaemonAvailable() {
+  try {
+    return run('docker', ['info'], { timeout: 15_000 }).status === 0;
+  } catch {
+    return false;
+  }
+}
+
+/** Parses `docker compose ps --format json` (JSON array or one object per line). */
+function parsePsJson(stdout) {
+  const text = String(stdout).trim();
+  if (!text) return [];
+  try {
+    const parsed = JSON.parse(text);
+    return Array.isArray(parsed) ? parsed : [parsed];
+  } catch {
+    return text
+      .split('\n')
+      .map((line) => line.trim())
+      .filter(Boolean)
+      .map((line) => JSON.parse(line));
+  }
+}
+
+/** Tolerant field lookup across compose ps JSON shapes. */
+function field(container, ...names) {
+  for (const name of names) {
+    if (container[name] !== undefined) return container[name];
+  }
+  return undefined;
+}
+
+/**
+ * Polls `docker compose ps` until the db container of the given project
+ * reports healthy (or the deadline passes), so the probe never races a
+ * still-booting database.
+ */
+function waitForDbHealthy(project, deadlineMs = 60_000) {
+  const deadline = Date.now() + deadlineMs;
+  let last = '';
+  while (Date.now() < deadline) {
+    const ps = run('docker', ['compose', '-p', project, 'ps', '--format', 'json'], {
+      cwd: REPO_ROOT,
+      timeout: 15_000,
+    });
+    if (ps.status === 0) {
+      last = ps.stdout;
+      const db = parsePsJson(ps.stdout).find((c) => field(c, 'Service', 'service') === 'db');
+      if (db && /healthy/i.test(String(field(db, 'Health', 'health') ?? ''))) return;
+    }
+    run(process.execPath, ['-e', 'setTimeout(() => {}, 1000)']); // db still booting — retry
+  }
+  throw new Error(`the db container did not become healthy within ${deadlineMs}ms (last ps: "${last.trim()}")`);
+}
+
+/**
+ * The host-side probe body: exercises the committed lock module against a
+ * real database (DATABASE_URL) exactly as concurrent migration runners will —
+ * first runner holds the lock, second runner fails fast AND waits, acquires
+ * after release, and a session that closes (the runner exits) releases the
+ * lock. Written to a temp file inside `packages/database-postgres/` so `pg`
+ * resolves through the package's own dependency links, then removed.
+ */
+const PROBE_SOURCE = `
+import { Pool, Client } from 'pg';
+import { MigrationLock, MIGRATION_LOCK_KEY } from './src/lock.ts';
+
+const pool = new Pool({ connectionString: process.env.DATABASE_URL });
+
+const advisoryCount = async () => {
+  const r = await pool.query(
+    "SELECT count(*)::int AS n FROM pg_locks WHERE locktype = 'advisory' AND granted",
+  );
+  return r.rows[0].n;
+};
+
+const advisoryWaitEvents = async () => {
+  const r = await pool.query(
+    \`SELECT wait_event_type, wait_event FROM pg_stat_activity
+       WHERE datname = current_database() AND pid <> pg_backend_pid()\`,
+  );
+  return r.rows
+    .filter((row) => row.wait_event_type !== null && row.wait_event !== null)
+    .map((row) => row.wait_event_type + ':' + row.wait_event);
+};
+
+const sleep = (ms) => new Promise((resolve) => setTimeout(resolve, ms));
+
+try {
+  const baseline = await advisoryCount();
+
+  // First runner takes the lock: the server must hold one granted advisory
+  // lock more than before.
+  const lockA = new MigrationLock(pool);
+  await lockA.acquire();
+  const heldCount = await advisoryCount();
+
+  // A second runner fails fast while the first holds the lock.
+  const lockB = new MigrationLock(pool);
+  const secondFailsFast = await lockB.tryAcquire();
+
+  // A second runner waits while the first holds the lock: the blocking
+  // acquire() must not resolve, and the server must report the waiting
+  // session (wait_event 'advisory').
+  const waitPromise = lockB.acquire();
+  let observedWait = false;
+  const waitDeadline = Date.now() + 15_000;
+  while (Date.now() < waitDeadline) {
+    if ((await advisoryWaitEvents()).includes('Lock:advisory')) {
+      observedWait = true;
+      break;
+    }
+    await sleep(100);
+  }
+
+  // First runner finishes -> the waiting runner acquires, then releases.
+  await lockA.release();
+  await waitPromise;
+  const secondAcquiredAfterRelease = lockB.isHeld;
+  await lockB.release();
+  const countAfterRelease = await advisoryCount();
+
+  // Session exit releases the lock (rollback note: "the lock releases when
+  // the runner exits"): a dedicated connection takes the same advisory lock
+  // and then closes; the server must release the lock with the session.
+  const exitClient = new Client({ connectionString: process.env.DATABASE_URL });
+  await exitClient.connect();
+  await exitClient.query('SELECT pg_advisory_lock(hashtextextended($1, 0))', [MIGRATION_LOCK_KEY]);
+  const heldWhileSessionOpen = await advisoryCount();
+  await exitClient.end(); // the runner exits -> session closes -> lock releases
+  let thirdAcquiresAfterSessionEnd = false;
+  const retryDeadline = Date.now() + 5_000;
+  while (Date.now() < retryDeadline) {
+    const lockC = new MigrationLock(pool);
+    if (await lockC.tryAcquire()) {
+      thirdAcquiresAfterSessionEnd = true;
+      await lockC.release();
+      break;
+    }
+    await sleep(100);
+  }
+
+  console.log('LOCK_PROBE_RESULT ' + JSON.stringify({
+    baseline,
+    heldCount,
+    secondFailsFast,
+    observedWait,
+    secondAcquiredAfterRelease,
+    countAfterRelease,
+    heldWhileSessionOpen,
+    thirdAcquiresAfterSessionEnd,
+  }));
+} finally {
+  await pool.end();
+}
+`;
+
+// ---------------------------------------------------------------------------
+// Criterion tests
+// ---------------------------------------------------------------------------
+
+test('the lock module exists in the driver-owner package and defines the migration lock key', () => {
+  assert.ok(existsSync(path.join(REPO_ROOT, LOCK_SRC)), `committed ${LOCK_SRC} must exist`);
+  const src = read(LOCK_SRC);
+  assertLockModule(src);
+});
+
+test('acquire() takes the blocking session-scoped advisory lock keyed by a bound parameter (a second runner waits)', () => {
+  assertBlockingAcquire(read(LOCK_SRC));
+});
+
+test('tryAcquire() fails fast while another runner holds the lock (a second runner fails)', () => {
+  assertNonBlockingAcquire(read(LOCK_SRC));
+});
+
+test('release() unlocks the holding session and returns the connection to the pool', () => {
+  assertSessionScopedRelease(read(LOCK_SRC));
+});
+
+test('the driver boundary re-exports the lock from the package entrypoint', () => {
+  const src = read(INDEX_SRC);
+  assert.match(
+    src,
+    /from '\.\/lock\.js'/,
+    'the driver boundary must import the lock module (from \'./lock.js\')',
+  );
+  assertBoundaryReexport(src);
+});
+
+test('the advisory-lock criterion is enforced in CI', () => {
+  // Picked up by the root test command (root `scripts.test` glob).
+  const scripts = JSON.parse(read('package.json')).scripts ?? {};
+  assert.equal(
+    scripts.test,
+    `node --test "${ROOT_TEST_GLOB}"`,
+    `root scripts.test must run the "${ROOT_TEST_GLOB}" glob so this suite runs with the rest`,
+  );
+  // And a dedicated CI job gates it on every PR.
+  const workflow = read('.gitea/workflows/ci.yml');
+  assert.ok(
+    workflow.includes(`node --test tests/database-postgres-lock.test.mjs`),
+    `CI must run the advisory-lock suite (job "${CI_JOB}") on every PR`,
+  );
+});
+
+// ---------------------------------------------------------------------------
+// Real-stack probe — the issue's test plan: "run a concurrent migration
+// lock test" against a real database
+// ---------------------------------------------------------------------------
+
+const DOCKER_COMPOSE = dockerComposeAvailable();
+const DOCKER_DAEMON = dockerDaemonAvailable();
+
+/** True when this Node can execute the committed `.ts` lock module (>= 23.6, type stripping). */
+const TS_STRIPPING = (() => {
+  const [major, minor] = process.versions.node.split('.').map(Number);
+  return major > 23 || (major === 23 && minor >= 6);
+})();
+
+// An isolated compose project + non-default host port so this probe never
+// collides with the compose-config suite's default-project containers, the
+// ledger probe's project/port, or the default 5432 binding when several
+// suites run on the same host.
+const COMPOSE_PROJECT = 'eppp-lock-probe';
+const POSTGRES_HOST_PORT = '55433';
+const DATABASE_URL = `postgres://eppp:eppp@127.0.0.1:${POSTGRES_HOST_PORT}/eppp`;
+
+test('concurrent migration runners are serialized by the advisory lock (real stack)', { skip: !DOCKER_COMPOSE || !DOCKER_DAEMON || !TS_STRIPPING }, () => {
+  // The issue's test plan: "run a concurrent migration lock test". The probe
+  // starts the committed compose `db` service (its own project + host port),
+  // runs the committed lock module against it with two runner instances, and
+  // asserts the first runner holds the lock, the second fails fast AND waits
+  // until the first releases (server-reported wait_event 'advisory'), and a
+  // session that closes — the runner exits — releases the lock (rollback
+  // note). Rollback: `docker compose -p eppp-lock-probe down`.
+  const composeEnv = { ...process.env, POSTGRES_PORT: POSTGRES_HOST_PORT };
+  const compose = (args, opts = {}) =>
+    run('docker', ['compose', '-p', COMPOSE_PROJECT, ...args], { cwd: REPO_ROOT, env: composeEnv, ...opts });
+
+  const probeFile = path.join(REPO_ROOT, 'packages/database-postgres', `.lock-probe-${process.pid}.mjs`);
+
+  try {
+    const up = compose(['up', '-d', 'db'], { timeout: 180_000 });
+    assert.equal(
+      up.status,
+      0,
+      `"docker compose up -d db" must exit 0:\n${(up.stdout || '')}\n${(up.stderr || '')}`.trim(),
+    );
+    waitForDbHealthy(COMPOSE_PROJECT);
+
+    // Run the committed lock module against the real database.
+    writeFileSync(probeFile, PROBE_SOURCE);
+    const probe = run(process.execPath, [probeFile], {
+      cwd: REPO_ROOT,
+      env: { ...process.env, DATABASE_URL },
+      timeout: 60_000,
+    });
+    assert.equal(
+      probe.status,
+      0,
+      `the lock probe must exit 0:\n${(probe.stdout || '')}\n${(probe.stderr || '')}`.trim(),
+    );
+    const resultLine = (probe.stdout || '')
+      .split('\n')
+      .map((l) => l.trim())
+      .find((l) => l.startsWith('LOCK_PROBE_RESULT'));
+    assert.ok(resultLine, `the lock probe must report a result line (stdout: "${(probe.stdout || '').trim()}")`);
+    const result = JSON.parse(resultLine.slice('LOCK_PROBE_RESULT'.length).trim());
+
+    // "advisory lock prevents concurrent migration runners": the first runner
+    // holds exactly one granted advisory lock more than the empty baseline.
+    assert.equal(
+      result.heldCount,
+      result.baseline + 1,
+      `acquire() must hold one granted advisory lock (baseline ${result.baseline}, got ${result.heldCount})`,
+    );
+
+    // "a second runner fails while the first holds the lock".
+    assert.equal(
+      result.secondFailsFast,
+      false,
+      'tryAcquire() must fail fast while the first runner holds the lock',
+    );
+
+    // "a second runner waits while the first holds the lock": the blocking
+    // acquire() does not resolve and the server reports the waiting session.
+    assert.equal(
+      result.observedWait,
+      true,
+      'the blocking acquire() must wait (server-reported wait_event advisory) while the first runner holds the lock',
+    );
+
+    // The waiting runner acquires once the first runner releases.
+    assert.equal(
+      result.secondAcquiredAfterRelease,
+      true,
+      'the waiting runner must acquire the lock once the first runner releases it',
+    );
+
+    // Nothing is left held after both runners release.
+    assert.equal(
+      result.countAfterRelease,
+      result.baseline,
+      `no advisory lock may remain granted after both runners release (got ${result.countAfterRelease}, expected ${result.baseline})`,
+    );
+
+    // Rollback note: "the lock releases when the runner exits" — a session
+    // that holds the lock and then closes releases it.
+    assert.equal(
+      result.heldWhileSessionOpen,
+      result.baseline + 1,
+      `the dedicated session must hold the advisory lock while open (baseline ${result.baseline}, got ${result.heldWhileSessionOpen})`,
+    );
+    assert.equal(
+      result.thirdAcquiresAfterSessionEnd,
+      true,
+      'the lock must be acquirable again after the holding session closes (the runner exits)',
+    );
+  } finally {
+    compose(['down', '-v'], { timeout: 120_000 });
+    rmSync(probeFile, { force: true });
+  }
+});
+
+// ---------------------------------------------------------------------------
+// Non-vacuous probes — the assertions above really do fail on violations
+// ---------------------------------------------------------------------------
+
+test('removing pg_advisory_lock makes the blocking-acquire criterion fail (mutation probe)', () => {
+  const src = read(LOCK_SRC);
+  const withoutBlocking = src.replace(/SELECT pg_advisory_lock\(/, 'SELECT pg_advisory_xact_lock(');
+  assert.notEqual(withoutBlocking, src, 'the mutation must actually replace the blocking lock call');
+  assert.throws(() => assertBlockingAcquire(withoutBlocking), /pg_advisory_lock/);
+});
+
+test('removing pg_try_advisory_lock makes the non-blocking criterion fail (mutation probe)', () => {
+  const src = read(LOCK_SRC);
+  const withoutTry = src.replace(/SELECT pg_try_advisory_lock\(/, 'SELECT pg_advisory_lock(');
+  assert.notEqual(withoutTry, src, 'the mutation must actually replace the non-blocking lock call');
+  assert.throws(() => assertNonBlockingAcquire(withoutTry), /pg_try_advisory_lock/);
+});
+
+test('interpolating the lock key into the SQL makes the keyed-parameter criterion fail (mutation probe)', () => {
+  const src = read(LOCK_SRC);
+  const interpolated = src.replace(/hashtextextended\(\$1, 0\)/g, "hashtextextended('${MIGRATION_LOCK_KEY}', 0)");
+  assert.notEqual(interpolated, src, 'the mutation must actually replace the $1 placeholder');
+  assert.throws(() => assertBlockingAcquire(interpolated), /\$1/);
+});
+
+test('removing pg_advisory_unlock makes the session-release criterion fail (mutation probe)', () => {
+  const src = read(LOCK_SRC);
+  const withoutUnlock = src.replace(/SELECT pg_advisory_unlock\(/, 'SELECT pg_advisory_lock(');
+  assert.notEqual(withoutUnlock, src, 'the mutation must actually replace the unlock call');
+  assert.throws(() => assertSessionScopedRelease(withoutUnlock), /pg_advisory_unlock/);
+});
+
+test('dropping the lock re-export from the boundary fails the boundary criterion (mutation probe)', () => {
+  const src = read(INDEX_SRC);
+  const withoutReexport = src.replace(/export \{ MigrationLock, MIGRATION_LOCK_KEY \} from '\.\/lock\.js';\n/, '');
+  assert.notEqual(withoutReexport, src, 'the mutation must actually remove the lock re-export');
+  assert.throws(() => assertBoundaryReexport(withoutReexport), /re-export/);
+});
+
+test('a placeholder lock module fails the advisory-lock criterion (mutation probe)', () => {
+  assert.throws(
+    () => assertLockModule('export class MigrationLock {}\n'),
+    /MIGRATION_LOCK_KEY/,
+  );
+});