fix(ack): bound worker polling and detect stale heartbeats

tests/test_ack_worker_probe.py

@@ -5,6 +5,7 @@ import io
 import json
 import sys
 import unittest
+from datetime import datetime, timezone
 from pathlib import Path
 from unittest import mock
 
@@ -62,12 +63,30 @@ class WorkerProbeClassifyTests(unittest.TestCase):
         self.assertEqual(result["status"], "stall")
         self.assertEqual(result["stallReason"], "usage-limit")
 
-    def test_heartbeat_means_progress_even_without_tail_markers(self) -> None:
+    def test_fresh_heartbeat_means_progress_even_without_tail_markers(self) -> None:
         result = worker_probe.classify(
-            "some unclassified output", "2026-08-23T12:00:00Z"
+            "some unclassified output",
+            "2026-08-23T12:00:00Z",
+            now=datetime(2026, 8, 23, 12, 2, tzinfo=timezone.utc),
         )
         self.assertEqual(result["status"], "progress")
         self.assertEqual(result["heartbeatAt"], "2026-08-23T12:00:00Z")
+        self.assertEqual(result["heartbeatAgeSeconds"], 120.0)
+
+    def test_stale_heartbeat_is_unknown_even_with_working_tail(self) -> None:
+        result = worker_probe.classify(
+            ["• Working (18m)"],
+            "2026-08-23T12:00:00Z",
+            now=datetime(2026, 8, 23, 12, 16, tzinfo=timezone.utc),
+        )
+        self.assertEqual(result["status"], "unknown")
+        self.assertEqual(result["stallReason"], "stale-heartbeat")
+        self.assertEqual(result["heartbeatAgeSeconds"], 960.0)
+
+    def test_invalid_heartbeat_is_unknown(self) -> None:
+        result = worker_probe.classify("some output", "not-a-timestamp")
+        self.assertEqual(result["status"], "unknown")
+        self.assertEqual(result["stallReason"], "invalid-heartbeat")
 
     def test_working_marker_means_running_without_heartbeat(self) -> None:
         result = worker_probe.classify(["• Working (12s)"], None)
@@ -87,6 +106,7 @@ class WorkerProbeClassifyTests(unittest.TestCase):
 
 class WorkerProbeMainTests(unittest.TestCase):
     def test_main_emits_single_json_with_progress(self) -> None:
+        fresh_heartbeat = worker_probe.utc_now().isoformat().replace("+00:00", "Z")
         with (
             mock.patch.object(
                 worker_probe,
@@ -97,7 +117,7 @@ class WorkerProbeMainTests(unittest.TestCase):
                 worker_probe,
                 "run_json",
                 side_effect=[
-                    dispatch_show(heartbeat="2026-08-23T12:00:00Z"),
+                    dispatch_show(heartbeat=fresh_heartbeat),
                     terminal_read(["Working (5s)"]),
                 ],
             ),