Fix /track-ws 404: install a WebSocket backend (websockets)

pyproject.toml

@@ -20,6 +20,13 @@ classifiers = [
 dependencies = [
     "fastapi>=0.136,<1",
     "uvicorn>=0.32,<1",
+    # The /track-ws endpoint needs a WebSocket protocol backend at runtime.
+    # Bare `uvicorn` ships none (it lives in the `[standard]` extra), so under
+    # gunicorn's UvicornWorker every upgrade 404s with "No supported WebSocket
+    # library detected". Depend on `websockets` directly — lighter than the
+    # full `[standard]` extra (no uvloop/httptools/watchfiles) and all the
+    # worker actually needs to accept the upgrade.
+    "websockets>=14,<17",
     "gunicorn>=23.0,<24",
     "httpx>=0.28,<1",
     "tenacity>=9.0,<10",

tests/test_app.py

@@ -196,3 +196,22 @@ async def receive():  # type: ignore[no-untyped-def]
     assert starts and starts[0]["status"] == 403
     # App was never called because the middleware short-circuited.
     assert ("app", GATED_PATH) not in received
+
+
+def test_uvicorn_has_websocket_backend() -> None:
+    """Guard the /track-ws upgrade against a missing WebSocket backend.
+
+    Under gunicorn's ``UvicornWorker`` the WebSocket upgrade only works if a
+    protocol library (``websockets`` or ``wsproto``) is installed. Bare
+    ``uvicorn`` ships neither — they live in the ``uvicorn[standard]`` extra —
+    so without an explicit dependency the env builds fine, tests pass via
+    Starlette's in-process TestClient, and yet every live ``/track-ws`` 404s
+    with "No supported WebSocket library detected". This asserts the backend
+    is present so that regression can't ship silently again.
+    """
+    import importlib.util
+
+    assert importlib.util.find_spec("websockets") or importlib.util.find_spec("wsproto"), (
+        "no WebSocket backend (websockets/wsproto) installed — /track-ws will 404 "
+        "under uvicorn; add `websockets` to project dependencies"
+    )