S00-012: Record blocked task and remediation handoff

Changes: Preserve incomplete work and blocker metadata for S00-012. This checkpoint does not mark implementation accepted.
Validation: Session ended with status blocked.
Blocker: Submit-transition descendant regression fails: repeated stop_process_tree after parent reap raises EPERM at os.killpg; launch OSError handling then attempts invalid escalation from review state.

Task: S00-012
Agent: auto-ci-cd-28868645424b
Role: ci-cd
Action: claim
Status: blocked

Task title: Fix runner prompt delivery after partial stdin timeout

tests/tooling/test_automation.py

@@ -276,6 +276,49 @@ else:
         self.assertEqual(result['stop'], 'session_limit')
         self.assertEqual(self.tracker.state()['tasks']['S00-001']['status'], 'blocked')
 
+    def _check_descendant_cleanup(self, transition):
+        import time
+        ready = self.root / 'state/descendant-ready'
+        late_write = self.root / 'src/late-descendant-write.txt'
+        child_code = (
+            "import pathlib,signal,time;signal.signal(signal.SIGTERM,signal.SIG_IGN);"
+            f"pathlib.Path({str(ready)!r}).write_text('ready');"
+            "time.sleep(1.5);"
+            f"pathlib.Path({str(late_write)!r}).write_text('unexpected')"
+        )
+        startup = (
+            "import subprocess,time\n"
+            f"subprocess.Popen([sys.executable,'-c',{child_code!r}])\n"
+            f"while not pathlib.Path({str(ready)!r}).exists():time.sleep(.01)\n"
+        )
+        fake = self.root / 'fake_agent.py'
+        source = fake.read_text().replace(
+            "prompt=sys.stdin.read();assert 'fresh session' in prompt",
+            startup + ("prompt=sys.stdin.read();assert 'fresh session' in prompt"
+                       if transition else "time.sleep(10)"))
+        fake.write_text(source + '\nimport time;time.sleep(10)\n')
+        (self.root / 'state/first-blocker').write_text('skip fixture blocker')
+        runner = RUN_MODULE.Runner(self.root, dict(self.config, max_sessions=1,
+                                                  timeout_seconds=2 if transition else .5))
+        result = runner.run()
+        self.assertEqual(result['launched'], 1)
+        self.assertTrue(ready.is_file(), 'Descendant must start before cleanup')
+        record = json.loads(next((self.root / 'state/runs').glob('*/run.json')).read_text())
+        self.assertEqual(record['stopped_after_transition'], transition)
+        self.assertEqual(self.tracker.state()['tasks']['S00-001']['status'],
+                         'review' if transition else 'blocked')
+        time.sleep(1.6)
+        self.assertFalse(late_write.exists(), 'Descendant survived process-group cleanup')
+        self.assertEqual(record['scope_violations'], [])
+
+    @unittest.skipUnless(sys.platform != 'win32', 'POSIX process-group cleanup')
+    def test_timeout_stops_source_writing_descendant(self):
+        self._check_descendant_cleanup(transition=False)
+
+    @unittest.skipUnless(sys.platform != 'win32', 'POSIX process-group cleanup')
+    def test_submit_transition_stops_source_writing_descendant(self):
+        self._check_descendant_cleanup(transition=True)
+
     def test_scope_matcher_checks_modified_created_deleted_files(self):
         self.assertEqual(RUN_MODULE.scope_violations({'a': 'old', 'gone': 'old'}, {'a': 'new', 'created': 'new'}, ['a']), ['created', 'gone'])