fix: Fix users unable to see or hear each other in voice channels due to

stale server sockets, passive non-initiators, and race conditions
during peer connection setup.

Fix users unable to see or hear each other in voice channels due to
stale server sockets, passive non-initiators, and race conditions
during peer connection setup.

Server:
- Close stale WebSocket connections sharing the same oderId in
  handleIdentify instead of letting them linger up to 45s
- Make user_joined/user_left broadcasts identity-aware so duplicate
  sockets don't produce phantom join/leave events
- Include serverIds in user_left payload for multi-room presence
- Simplify findUserByOderId now that stale sockets are cleaned up

Client - signaling:
- Add fallback offer system with 1s timer for missed user_joined races
- Add non-initiator takeover after 5s when the initiator fails to send
  an offer (NON_INITIATOR_GIVE_UP_MS)
- Scope peerServerMap per signaling URL to prevent cross-server
  collisions
- Add socket identity guards on all signaling event handlers
- Replace canReusePeerConnection with hasActivePeerConnection and
  isPeerConnectionNegotiating with extended grace periods

Client - peer connections:
- Extract replaceUnusablePeer helper to deduplicate stale peer
  replacement in offer and ICE handlers
- Add stale connectionstatechange guard to ignore events from replaced
  RTCPeerConnection instances
- Use deterministic initiator election in peer recovery reconnects
- Track createdAt on PeerData for staleness detection

Client - presence:
- Add multi-room presence tracking via presenceServerIds on User
- Replace clearUsers + individual userJoined with syncServerPresence
  for atomic server roster updates
- Make userLeft handle partial server removal instead of full eviction

Documentation:
- Add server-side connection hygiene, non-initiator takeover, and stale
  peer replacement sections to the realtime README

server/src/websocket/index.ts

@@ -6,7 +6,11 @@ import {
 import { WebSocketServer, WebSocket } from 'ws';
 import { v4 as uuidv4 } from 'uuid';
 import { connectedUsers } from './state';
-import { broadcastToServer } from './broadcast';
+import {
+  broadcastToServer,
+  getServerIdsForOderId,
+  isOderIdConnectedToServer
+} from './broadcast';
 import { handleWebSocketMessage } from './handler';
 
 /** How often to ping all connected clients (ms). */
@@ -20,13 +24,19 @@ function removeDeadConnection(connectionId: string): void {
   if (user) {
     console.log(`Removing dead connection: ${user.displayName ?? 'Unknown'} (${user.oderId})`);
 
+    const remainingServerIds = getServerIdsForOderId(user.oderId, connectionId);
+
     user.serverIds.forEach((sid) => {
+      if (isOderIdConnectedToServer(user.oderId, sid, connectionId)) {
+        return;
+      }
+
       broadcastToServer(sid, {
         type: 'user_left',
         oderId: user.oderId,
         displayName: user.displayName,
         serverId: sid,
-        serverIds: []
+        serverIds: remainingServerIds
       }, user.oderId);
     });