diff --git a/packages/database-postgres/src/lock.ts b/packages/database-postgres/src/lock.ts
index 413b352..d00e52d 100644
--- a/packages/database-postgres/src/lock.ts
+++ b/packages/database-postgres/src/lock.ts
@@ -21,9 +21,11 @@
  *     (`pool.connect()`), so the lock never taints a pooled connection that
  *     other queries share;
  *   - released explicitly by `release()` (`pg_advisory_unlock` first, then
- *     the client goes back to the pool), and released implicitly by the
- *     server when the holding session ends — the issue's rollback note: "the
- *     lock releases when the runner exits".
+ *     the client goes back to the pool; if the unlock statement itself fails,
+ *     the connection is destroyed — `client.release(error)` — so a pooled
+ *     connection is never reused while its session still holds the lock),
+ *     and released implicitly by the server when the holding session ends —
+ *     the issue's rollback note: "the lock releases when the runner exits".
  *
  * The lock key is always passed as a bound parameter (`$1`) — the SQL never
  * interpolates it, so the only interpolated value is the `$1` placeholder
@@ -133,7 +135,12 @@ export class MigrationLock {
    * Releases the advisory lock: unlocks it on the holding session
    * (`pg_advisory_unlock`) and returns the connection to the pool, so the
    * lock is gone before any other query could reuse that pooled connection.
-   * Idempotent: releasing an instance that does not hold the lock is a no-op.
+   * If the unlock statement fails (e.g. statement timeout or cancellation)
+   * the connection is destroyed instead — `client.release(error)` tells the
+   * pool to drop the client, ending the session (and its lock), so a pooled
+   * connection is never reused while its session still holds the lock; the
+   * failure is re-thrown. Idempotent: releasing an instance that does not
+   * hold the lock is a no-op.
    */
   async release(): Promise<void> {
     if (!this.held || this.client === null) return;
@@ -145,8 +152,15 @@ export class MigrationLock {
         'SELECT pg_advisory_unlock(hashtextextended($1, 0))',
         [MIGRATION_LOCK_KEY],
       );
-    } finally {
-      client.release();
+    } catch (error) {
+      // The unlock statement failed while this session may still hold the
+      // advisory lock. The connection must not go back into the pool in that
+      // state — the next borrower would block every other runner. Destroy it
+      // (release(error) removes the client from the pool), so the session —
+      // and its lock — ends.
+      client.release(error as Error);
+      throw error;
     }
+    client.release();
   }
 }
diff --git a/tests/database-postgres-lock.test.mjs b/tests/database-postgres-lock.test.mjs
index 1b0dabe..016c1ed 100644
--- a/tests/database-postgres-lock.test.mjs
+++ b/tests/database-postgres-lock.test.mjs
@@ -28,6 +28,13 @@
  *     connection leaks; the real-stack probe proves it behaviorally (two
  *     concurrent acquire() calls → `pool.totalCount` stays 1, one granted
  *     advisory lock, none left after release).
+ *   - the release() failure path (reviewer finding F4): if the
+ *     `pg_advisory_unlock` statement fails, `release()` destroys the
+ *     connection (`client.release(error)` — the pool drops the client, ending
+ *     the session and its lock) instead of returning it to the pool, so a
+ *     pooled connection is never reused while its session still holds the
+ *     lock; locked in statically, by a mutation probe, and behaviorally by a
+ *     deterministic stub-pool probe of the committed module's control flow.
  *   - 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.
@@ -169,6 +176,40 @@ function assertSessionScopedRelease(src) {
   );
 }
 
+/**
+ * Asserts the unlock-failure path (F4): when the `pg_advisory_unlock`
+ * statement fails, `release()` must DESTROY the connection —
+ * `client.release(error)` tells the pool to drop the client, ending the
+ * session (and its advisory lock) — so a pooled connection is never reused
+ * while its session still holds the lock. The plain `client.release()`
+ * (returning the connection to the pool) must live only on the success path,
+ * after the unlock try/catch.
+ */
+function assertReleaseDestroysOnUnlockFailure(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,
+    /catch \(error\) \{[\s\S]*?client\.release\(error/,
+    'on unlock failure release() must destroy the connection (client.release(error) in the catch of the unlock query)',
+  );
+  const destroyIdx = releaseBody.indexOf('client.release(error');
+  const catchIdx = releaseBody.indexOf('catch (error) {');
+  const plainReleaseIdx = releaseBody.indexOf('client.release()');
+  assert.ok(
+    destroyIdx !== -1 &&
+      catchIdx !== -1 &&
+      plainReleaseIdx !== -1 &&
+      destroyIdx < plainReleaseIdx &&
+      catchIdx < plainReleaseIdx,
+    'the plain client.release() (return to pool) must come after the unlock failure handling (destroy path) — a still-locked connection is never returned to the pool',
+  );
+}
+
 /** Asserts the driver boundary re-exports the lock from the package entrypoint. */
 function assertBoundaryReexport(src) {
   assert.match(
@@ -388,6 +429,83 @@ try {
 }
 `;
 
+/**
+ * Deterministic behavioral probe of the release() failure path (F4): models
+ * pg's PoolClient disposal contract — release() returns the client to the
+ * pool, release(error) destroys it (the pool removes the client, ending its
+ * session) — and drives the COMMITTED lock module's release() directly with a
+ * stub pool, so the check is about the module's behavior (which disposal call
+ * it makes), not its source shape. No database or Docker needed.
+ */
+const RELEASE_FAILURE_PROBE_SOURCE = `
+import { MigrationLock } from './src/lock.ts';
+
+// A stub pg pool whose client fails (or succeeds) the unlock query and
+// records how release() disposes of it.
+const makeStub = (unlockSucceeds) => {
+  const events = [];
+  const client = {
+    async query() {
+      if (unlockSucceeds) {
+        events.push('unlock:ok');
+        return { rows: [] };
+      }
+      const err = new Error('unlock statement failed (statement timeout)');
+      err.code = '57014';
+      events.push('unlock:fail');
+      throw err;
+    },
+    release(error) {
+      events.push(error === undefined ? 'release()' : 'release(error)');
+      if (error !== undefined) client.destroyed = true;
+    },
+  };
+  const pool = { connect: async () => client };
+  return { pool, client, events };
+};
+
+const results = {};
+
+// Failure path: the unlock query rejects -> release() must DESTROY the
+// connection (release(error)), not return it to the pool while its session
+// still holds the advisory lock.
+{
+  const { pool, client, events } = makeStub(false);
+  const lock = new MigrationLock(pool);
+  lock.held = true; // drive the committed release() directly (no DB needed)
+  lock.client = client;
+  let rejected = false;
+  try {
+    await lock.release();
+  } catch (error) {
+    rejected = String(error.message).includes('unlock statement failed');
+  }
+  results.failurePath = {
+    rejected,
+    events,
+    destroyed: client.destroyed === true,
+    stateCleared: lock.isHeld === false && lock.client === null,
+  };
+}
+
+// Success path: the unlock query resolves -> release() returns the connection
+// to the pool with the plain release().
+{
+  const { pool, client, events } = makeStub(true);
+  const lock = new MigrationLock(pool);
+  lock.held = true;
+  lock.client = client;
+  await lock.release();
+  results.successPath = {
+    events,
+    destroyed: client.destroyed === true,
+    stateCleared: lock.isHeld === false && lock.client === null,
+  };
+}
+
+console.log('LOCK_RELEASE_FAILURE_PROBE_RESULT ' + JSON.stringify(results));
+`;
+
 // ---------------------------------------------------------------------------
 // Criterion tests
 // ---------------------------------------------------------------------------
@@ -414,6 +532,10 @@ test('release() unlocks the holding session and returns the connection to the po
   assertSessionScopedRelease(read(LOCK_SRC));
 });
 
+test('release() destroys the connection when the unlock statement fails (never reuses a still-locked connection)', () => {
+  assertReleaseDestroysOnUnlockFailure(read(LOCK_SRC));
+});
+
 test('the driver boundary re-exports the lock from the package entrypoint', () => {
   const src = read(INDEX_SRC);
   assert.match(
@@ -590,6 +712,68 @@ test('concurrent migration runners are serialized by the advisory lock (real sta
   }
 });
 
+test('release() destroys the connection on unlock failure and returns it to the pool on success (behavioral probe)', { skip: !TS_STRIPPING }, () => {
+  // F4: pg's release(error) destroys the client (the pool removes it, ending
+  // the session and its lock); the plain release() returns it to the pool.
+  // The probe drives the committed release() with a stub pool: a failed unlock
+  // must take the destroy path (release(error)), a successful unlock the
+  // return path (plain release()) — a still-locked connection is never reused.
+  const probeFile = path.join(REPO_ROOT, 'packages/database-postgres', `.lock-probe-release-${process.pid}.mjs`);
+  try {
+    writeFileSync(probeFile, RELEASE_FAILURE_PROBE_SOURCE);
+    const probe = run(process.execPath, [probeFile], { cwd: REPO_ROOT, timeout: 30_000 });
+    assert.equal(
+      probe.status,
+      0,
+      `the release-failure probe must exit 0:\n${(probe.stdout || '')}\n${(probe.stderr || '')}`.trim(),
+    );
+    const resultLine = (probe.stdout || '')
+      .split('\n')
+      .map((l) => l.trim())
+      .find((l) => l.startsWith('LOCK_RELEASE_FAILURE_PROBE_RESULT'));
+    assert.ok(resultLine, `the release-failure probe must report a result line (stdout: "${(probe.stdout || '').trim()}")`);
+    const result = JSON.parse(resultLine.slice('LOCK_RELEASE_FAILURE_PROBE_RESULT'.length).trim());
+
+    // Failure path: the unlock statement failed -> the connection is destroyed
+    // (release(error)), never returned to the pool while still locked.
+    assert.equal(
+      result.failurePath.rejected,
+      true,
+      'release() must reject when the unlock statement fails',
+    );
+    assert.deepEqual(
+      result.failurePath.events,
+      ['unlock:fail', 'release(error)'],
+      'on unlock failure release() must destroy the connection (client.release(error)), not return it to the pool',
+    );
+    assert.equal(
+      result.failurePath.destroyed,
+      true,
+      'the failed-unlock connection must be destroyed (removed from the pool)',
+    );
+    assert.equal(
+      result.failurePath.stateCleared,
+      true,
+      'release() must clear held/client even on the failure path',
+    );
+
+    // Success path: the unlock succeeded -> the connection is returned to the
+    // pool with the plain release().
+    assert.deepEqual(
+      result.successPath.events,
+      ['unlock:ok', 'release()'],
+      'on a successful unlock release() must return the connection to the pool (plain client.release())',
+    );
+    assert.equal(
+      result.successPath.destroyed,
+      false,
+      'a successful unlock must not destroy the connection',
+    );
+  } finally {
+    rmSync(probeFile, { force: true });
+  }
+});
+
 // ---------------------------------------------------------------------------
 // Non-vacuous probes — the assertions above really do fail on violations
 // ---------------------------------------------------------------------------
@@ -622,6 +806,15 @@ test('removing pg_advisory_unlock makes the session-release criterion fail (muta
   assert.throws(() => assertSessionScopedRelease(withoutUnlock), /pg_advisory_unlock/);
 });
 
+test('returning the connection to the pool on unlock failure makes the failure-path criterion fail (mutation probe)', () => {
+  const src = read(LOCK_SRC);
+  // The buggy shape F4 describes: a try/finally that always returns the client
+  // to the pool, so a failed unlock reuses a still-locked connection.
+  const withoutDestroy = src.replace('client.release(error as Error);', 'client.release();');
+  assert.notEqual(withoutDestroy, src, 'the mutation must actually replace the failure-path destroy with a plain release');
+  assert.throws(() => assertReleaseDestroysOnUnlockFailure(withoutDestroy), /client\.release\(error/);
+});
+
 test('removing the in-flight acquire memo makes the re-entrancy criterion fail (mutation probe)', () => {
   const src = read(LOCK_SRC);
   const withoutMemo = src.replace(/if \(this\.acquireInFlight !== null\) return this\.acquireInFlight;\n/, '');