Improve local agent chat and device health detection

tests/test_device_manager.py

@@ -30,3 +30,19 @@ def test_device_manager_marks_unreachable_device_offline() -> None:
         manager.connect("iphone-1", max_retries=2, retry_backoff_seconds=0)
 
     assert manager.status("iphone-1") == "offline"
+
+
+def test_probe_marks_connected_device_offline_when_driver_is_unreachable() -> None:
+    class BrokenDriver:
+        def connect(self) -> None:
+            return None
+
+        def screenshot(self) -> bytes:
+            raise RuntimeError("WDA disconnected")
+
+    manager = DeviceManager()
+    manager.register_device("iphone-1", lambda: BrokenDriver())  # type: ignore[arg-type]
+    manager.connect("iphone-1")
+
+    assert manager.probe("iphone-1") is False
+    assert manager.status("iphone-1") == "offline"