fix(client_utils): connector with any_stream_is_registered check

bec_widgets/cli/client_utils.py

@@ -712,10 +712,13 @@ class BECGuiClient(RPCBase):
 
     def _start(self, wait: bool = False) -> None:
         self._killed = False
-        self._client.connector.unregister(cb=self._handle_registry_update)
-        self._client.connector.register(
-            MessageEndpoints.gui_registry_state(self._gui_id), cb=self._handle_registry_update
-        )
+        endpoint = MessageEndpoints.gui_registry_state(self._gui_id)
+        # connect_to_gui_server may already have registered this callback with from_start=True;
+        # replacing that subscription here would lose the replay of the current registry state.
+        if not self._client.connector.any_stream_is_registered(
+            endpoint, cb=self._handle_registry_update
+        ):
+            self._client.connector.register(endpoint, cb=self._handle_registry_update)
         return self._start_server(wait=wait)
 
     def _handle_registry_update(self, msg: dict[str, GUIRegistryStateMessage]) -> None:

tests/unit_tests/test_client_utils.py

@@ -309,6 +309,40 @@ def test_client_utils_gui_client_set_rpc_timeout():
     assert gui._rpc_timeout == 10
 
 
+def test_client_utils_start_preserves_connect_to_gui_server_subscription():
+    """
+    Regression test for `bec --gui-id <id>`: connect_to_gui_server registers the registry-state
+    stream with from_start=True so the current state of an already-running server is replayed.
+    The subsequent show() -> _start() must not replace that subscription with a plain one.
+    """
+    gui = BECGuiClient()
+    gui._client = mock.MagicMock()
+    connector = gui._client.connector
+
+    gui.connect_to_gui_server("external_gui")
+    assert connector.register.call_args.kwargs["from_start"] is True
+
+    connector.any_stream_is_registered.return_value = True
+    with mock.patch.object(gui, "_start_server"):
+        gui._start(wait=False)
+
+    connector.register.assert_called_once()
+    connector.unregister.assert_called_once()  # only the one from connect_to_gui_server
+
+
+def test_client_utils_start_registers_registry_state_when_missing():
+    gui = BECGuiClient()
+    gui._client = mock.MagicMock()
+    connector = gui._client.connector
+    connector.any_stream_is_registered.return_value = False
+
+    with mock.patch.object(gui, "_start_server") as mock_start_server:
+        gui._start(wait=False)
+
+    connector.register.assert_called_once()
+    mock_start_server.assert_called_once_with(wait=False)
+
+
 def test_client_utils_kill_server_waits_for_process_before_joining_output_thread():
     gui = BECGuiClient()
     gui._client = mock.MagicMock()