fix(chat): prevent stale websocket close handler from triggering reconnect loop

frontend/src/main.test.ts

@@ -253,6 +253,25 @@ describe("WebSocket reconnect", () => {
     expect(websocketInstances).toHaveLength(2);
     expect(websocketInstances[1].url).toContain("room=lobby");
   });
+
+  it("does not reconnect from a socket that was intentionally replaced", async () => {
+    vi.useFakeTimers();
+
+    window.switchRoom("lobby");
+    expect(websocketInstances).toHaveLength(1);
+    const replaced = websocketInstances[0];
+
+    // A room switch intentionally replaces the socket; the old socket must not
+    // schedule its own reconnect, otherwise history is re-pulled on a loop.
+    window.switchRoom("main");
+    expect(websocketInstances).toHaveLength(2);
+    expect(replaced.onclose).toBeNull();
+
+    replaced.onclose?.();
+    await vi.advanceTimersByTimeAsync(3000);
+
+    expect(websocketInstances).toHaveLength(2);
+  });
 });
 
 describe("URL resolution", () => {