Refuse websocket upgrades with HTTP statuses, not close codes

A close() before accept() carries the HTTP status of the refused
upgrade, not a WebSocket close code: RSGI (granian) uses the value
verbatim as the response status, so 4401 panicked on the invalid status
(InvalidStatusCode) and — granian being built with panic = "abort" —
aborted the worker and took the whole app down. ASGI servers answer 403
regardless, and browsers report a refused handshake as an abnormal close
(1006), so the 4401/4403/4404 codes never reached clients anyway.

Reject 401/404/403 to mirror GET /api/games/{id}, and classify a failed
first connection in the game page through the REST API so players still
see "session expired" / "game no longer available" instead of a retry
loop. Add a regression test asserting every pre-accept rejection uses a
status in the HTTP range.

server/packages/tavolo-platform/tests/test_ws.py

@@ -2,12 +2,46 @@
 from __future__ import annotations
 
 import unittest
+from typing import Any, Mapping, Sequence
 
 from httpx import ASGITransport, AsyncClient
 from httpx_ws import WebSocketDisconnect, aconnect_ws
 from httpx_ws.transport import ASGIWebSocketTransport
+from kaya.core import WebSocket, WebSocketMessage
 
 from helpers import async_test, make_platform, make_user, oidc_user, ws_users
+from tavolo.platform import GameSession, Seat
+
+
+class RecordingSocket(WebSocket):
+    """A socket that only records pre-accept rejections."""
+
+    def __init__(self, path: str) -> None:
+        self.path = path
+        self.query_string = ""
+        self.scheme = "ws"
+        self.headers: Mapping[str, Sequence[str]] = {}
+        self.client = ("127.0.0.1", 12345)
+        self.server = ("127.0.0.1", 80)
+        self.close_codes: list[int] = []
+
+    async def accept(self, headers: Any = None) -> None:
+        raise AssertionError("a rejected socket must not be accepted")
+
+    async def receive(self) -> WebSocketMessage:
+        raise AssertionError("a rejected socket must not receive")
+
+    async def send_text(self, data: str) -> None:
+        raise AssertionError("a rejected socket must not send")
+
+    async def send_bytes(self, data: bytes) -> None:
+        raise AssertionError("a rejected socket must not send")
+
+    async def close(self, code: int = 1000) -> None:
+        self.close_codes.append(code)
+
+    async def __anext__(self) -> WebSocketMessage:
+        raise AssertionError("a rejected socket must not receive")
 
 
 class WebSocketTest(unittest.TestCase):
@@ -124,7 +158,7 @@ class WebSocketTest(unittest.TestCase):
                 with self.assertRaises(WebSocketDisconnect) as caught:
                     async with aconnect_ws("/ws/games/no-such-game", ws_client):
                         pass
-                self.assertEqual(4404, caught.exception.code)
+                self.assertEqual(404, caught.exception.code)
 
     @async_test
     async def test_non_player_is_closed(self) -> None:
@@ -140,7 +174,7 @@ class WebSocketTest(unittest.TestCase):
                     with self.assertRaises(WebSocketDisconnect) as caught:
                         async with aconnect_ws(f"/ws/games/{game_id}", ws_client):
                             pass
-                    self.assertEqual(4403, caught.exception.code)
+                    self.assertEqual(403, caught.exception.code)
 
     @async_test
     async def test_unauthenticated_is_closed(self) -> None:
@@ -151,7 +185,45 @@ class WebSocketTest(unittest.TestCase):
                 with self.assertRaises(WebSocketDisconnect) as caught:
                     async with aconnect_ws("/ws/games/whatever", ws_client):
                         pass
-                self.assertEqual(4401, caught.exception.code)
+                self.assertEqual(401, caught.exception.code)
+
+
+class RejectionStatusTest(unittest.TestCase):
+    """Pre-accept rejections must carry HTTP statuses, not close codes.
+
+    Granian's RSGI layer uses the value passed to ``close()`` before
+    ``accept()`` as the HTTP status of the refused upgrade; a WebSocket
+    close code like 4401 is not a valid status and panics the worker
+    (``InvalidStatusCode``, and with ``panic = "abort"`` the whole app
+    dies). Drive the rejections through the app with a recording socket
+    so the invariant is checked without a real server.
+    """
+
+    @async_test
+    async def test_pre_accept_rejections_are_http_statuses(self) -> None:
+        app, platform, _ = make_platform()
+        session = GameSession(
+            id="seated-game",
+            game_type="dummy",
+            join_code="SEAT01",
+            creator_sub="alice",
+            players=[Seat(user_sub="alice", display_name="Alice")],
+        )
+        engine = platform.registry.require("dummy")
+        engine.create(session, {})
+        await platform.game_store.save(session)
+        cases = [
+            ("unauthenticated", [], "/ws/games/whatever", 401),
+            ("unknown game", [make_user("alice")], "/ws/games/no-such-game", 404),
+            ("not seated", [make_user("mallory")], f"/ws/games/{session.id}", 403),
+        ]
+        for label, users, path, expected in cases:
+            ws = RecordingSocket(path)
+            with ws_users(users):
+                await app.handle_websocket(ws)
+            self.assertEqual([expected], ws.close_codes, label)
+            for code in ws.close_codes:
+                self.assertTrue(100 <= code <= 599, f"{label}: {code} is not an HTTP status")
 
 
 if __name__ == "__main__":