Double-start guard: launching marker, probe-and-adopt, fresh-dir relaunch; skip unreachable terminals per tick

Before the launch call the planned run (run id, terminal, handle, bookkeeping) is saved as a launching
marker. If the launch call fails or agentd dies before recording the run, the next tick probes the run
directory (exit.txt / launch.pid / pid.txt): evidence -> adopt the run; nothing -> relaunch with the same
run id in <run_id>-r2 (-r3 ...); probe unreachable -> keep the marker, which holds the terminal slot.
Transports refuse to clean a run directory holding a pid file. A terminal whose relay fails is skipped
for the rest of the tick (heartbeat.down) while other terminals carry on.

tests/test_transports.py

@@ -120,3 +120,30 @@ class StoreTest(unittest.TestCase):
 
 if __name__ == "__main__":
     unittest.main()
+
+
+class GuardTest(unittest.TestCase):
+    def test_local_clean_refuses_dir_with_pid_file(self):
+        from agentd.transports import TransportError
+        with tempfile.TemporaryDirectory() as tmp:
+            t = LocalTransport(Config(config_data()), "oregon")
+            (Path(tmp) / "prompt.md").write_text("x")
+            t.mkdir(tmp, clean=True)
+            self.assertEqual(t.probe(tmp, ("exit.txt", "pid.txt")), [])
+            (Path(tmp) / "pid.txt").write_text("1")
+            with self.assertRaises(TransportError):
+                t.mkdir(tmp, clean=True)
+            self.assertEqual(t.probe(tmp, ("exit.txt", "pid.txt")), ["pid.txt"])
+
+    def test_windows_probe_and_clean_guard(self):
+        from agentd.transports import TransportError
+        cfg = config.load(ROOT / "config" / "agentd.example.yaml")
+        t = WindowsWarpgateTransport(cfg, "win10")
+        scripts = []
+        t.ps = lambda s, timeout=150: (scripts.append(s), "PROBE=launch.pid,pid.txt\n")[1]
+        self.assertEqual(t.probe("C:\\r\\GW-1-1", ("exit.txt", "launch.pid", "pid.txt")), ["launch.pid", "pid.txt"])
+        self.assertIn("Join-Path $d $_", scripts[-1])
+        t.ps = lambda s, timeout=150: (scripts.append(s), "HASPID\n")[1]
+        with self.assertRaises(TransportError):
+            t.mkdir("C:\\r\\GW-1-1", clean=True)
+        self.assertIn("'pid.txt'", scripts[-1])