fix(web): close P3 chat re-review findings

apps/web/src/lib/socket.spec.ts

@@ -10,25 +10,45 @@ vi.mock('socket.io-client', () => ({
 
 import { destroySocket, getSocket } from './socket';
 
-function createMockSocket(): {
+interface MockChatSocket {
   on: ReturnType<typeof vi.fn>;
   offAny: ReturnType<typeof vi.fn>;
   disconnect: ReturnType<typeof vi.fn>;
-} {
-  const mockSocket = {
-    on: vi.fn(() => mockSocket),
+  /** Test-only helper: fires every handler registered for `event` via
+   * `.on`, mirroring how a real socket.io-client instance invokes its own
+   * listeners (e.g. calling the registered `disconnect` handler(s) on a
+   * real transient disconnect). */
+  trigger(event: string): void;
+}
+
+function createMockSocket(): MockChatSocket {
+  const handlers = new Map<string, Set<() => void>>();
+  const mockSocket: MockChatSocket = {
+    on: vi.fn((event: string, handler: () => void) => {
+      if (!handlers.has(event)) handlers.set(event, new Set());
+      handlers.get(event)?.add(handler);
+      return mockSocket;
+    }),
     offAny: vi.fn(() => mockSocket),
     disconnect: vi.fn(() => mockSocket),
+    trigger(event: string): void {
+      for (const handler of handlers.get(event) ?? []) handler();
+    },
   };
   return mockSocket;
 }
 
+let currentMock!: MockChatSocket;
+
 describe('chat socket', () => {
   beforeEach(() => {
     ioMock.mockReset();
     // A fresh object per io() call so identity assertions (same singleton vs.
     // a genuinely new instance) are meaningful.
-    ioMock.mockImplementation(() => createMockSocket());
+    ioMock.mockImplementation(() => {
+      currentMock = createMockSocket();
+      return currentMock;
+    });
   });
 
   afterEach(() => {
@@ -52,9 +72,14 @@ describe('chat socket', () => {
     const first = getSocket();
 
     // socket.ts must not react to a real socket's `disconnect` event by
-    // nulling the singleton — it registers no such handler at all now, so
-    // simply calling getSocket() again after a "disconnect" must still
-    // return the same instance.
+    // nulling the singleton — it registers no such handler at all now.
+    // Actually fire every handler registered via `.on('disconnect', ...)`
+    // (mirroring a real socket.io-client reconnect) instead of merely
+    // calling getSocket() again: this is what makes the test fail if
+    // production reintroduces `socket.on('disconnect', () => { socket =
+    // null; })`, since that handler would run here and null the singleton
+    // before the next getSocket() call.
+    currentMock.trigger('disconnect');
     const second = getSocket();
 
     expect(second).toBe(first);