fix(server): initialize COM for Windows camera discovery

lelab/server.py

@@ -1004,6 +1004,28 @@ def _generic_cv2_cameras(backend) -> list[dict[str, Any]]:
     return cameras
 
 
+@contextlib.contextmanager
+def _windows_com_initialized():
+    """Initialize COM for the current Windows worker thread when available."""
+    try:
+        import comtypes
+    except ImportError:
+        yield
+        return
+
+    try:
+        comtypes.CoInitialize()
+    except OSError as e:
+        logger.warning("Windows COM initialization failed: %s", e)
+        yield
+        return
+
+    try:
+        yield
+    finally:
+        comtypes.CoUninitialize()
+
+
 def _windows_cameras() -> list[dict[str, Any]]:
     """Enumerate Windows cameras with their real DirectShow names.
 
@@ -1013,16 +1035,17 @@ def _windows_cameras() -> list[dict[str, Any]]:
     frontend match each index to the browser's ``MediaDeviceInfo.label`` for the
     live preview. Falls back to generic names if pygrabber is unavailable.
     """
-    try:
-        from pygrabber.dshow_graph import FilterGraph
+    with _windows_com_initialized():
+        try:
+            from pygrabber.dshow_graph import FilterGraph
 
-        names = FilterGraph().get_input_devices()
-    except Exception as e:  # ImportError, or a COM/DirectShow failure
-        logger.warning("pygrabber unavailable; using generic camera names: %s", e)
-        import cv2
+            names = FilterGraph().get_input_devices()
+        except Exception as e:  # ImportError, or a COM/DirectShow failure
+            logger.warning("pygrabber unavailable; using generic camera names: %s", e)
+            import cv2
 
-        return _generic_cv2_cameras(cv2.CAP_DSHOW)
-    return [{"index": i, "name": name, "available": True} for i, name in enumerate(names)]
+            return _generic_cv2_cameras(cv2.CAP_DSHOW)
+        return [{"index": i, "name": name, "available": True} for i, name in enumerate(names)]
 
 
 def _v4l2_camera_name(index: int) -> str | None:

tests/test_server.py

@@ -160,6 +160,44 @@ def _install_fake_pygrabber(monkeypatch: pytest.MonkeyPatch, filter_graph_cls) -
     monkeypatch.setitem(sys.modules, "pygrabber.dshow_graph", module)
 
 
+def _install_fake_comtypes(
+    monkeypatch: pytest.MonkeyPatch,
+    co_initialize,
+    co_uninitialize,
+) -> None:
+    import sys
+    import types
+
+    module = types.ModuleType("comtypes")
+    module.CoInitialize = co_initialize
+    module.CoUninitialize = co_uninitialize
+    monkeypatch.setitem(sys.modules, "comtypes", module)
+
+
+def test_windows_cameras_initializes_com_in_worker_thread(monkeypatch: pytest.MonkeyPatch) -> None:
+    """DirectShow is called only while COM is initialized for this thread."""
+    from lelab import server
+
+    events = []
+
+    class _FakeGraph:
+        def get_input_devices(self) -> list[str]:
+            events.append("enumerate")
+            return ["USB webcam"]
+
+    _install_fake_comtypes(
+        monkeypatch,
+        lambda: events.append("initialize"),
+        lambda: events.append("uninitialize"),
+    )
+    _install_fake_pygrabber(monkeypatch, _FakeGraph)
+
+    assert server._windows_cameras() == [
+        {"index": 0, "name": "USB webcam", "available": True},
+    ]
+    assert events == ["initialize", "enumerate", "uninitialize"]
+
+
 def test_windows_cameras_uses_real_directshow_names(monkeypatch: pytest.MonkeyPatch) -> None:
     """The Windows path returns pygrabber's real device names in index order so
     the frontend can match each camera to its browser deviceId (issues #12/#16).