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

toju-app/src/app/store/users/users.reducer.ts

@@ -7,6 +7,105 @@ import {
 import { User, BanEntry } from '../../shared-kernel';
 import { UsersActions } from './users.actions';
 
+function normalizePresenceServerIds(serverIds: readonly string[] | undefined): string[] | undefined {
+  if (!Array.isArray(serverIds)) {
+    return undefined;
+  }
+
+  const normalized = Array.from(new Set(
+    serverIds.filter((serverId): serverId is string => typeof serverId === 'string' && serverId.trim().length > 0)
+  ));
+
+  return normalized.length > 0 ? normalized : undefined;
+}
+
+function mergePresenceServerIds(
+  existingServerIds: readonly string[] | undefined,
+  incomingServerIds: readonly string[] | undefined
+): string[] | undefined {
+  return normalizePresenceServerIds([...(existingServerIds ?? []), ...(incomingServerIds ?? [])]);
+}
+
+function buildDisconnectedVoiceState(user: User): User['voiceState'] {
+  if (!user.voiceState) {
+    return undefined;
+  }
+
+  return {
+    ...user.voiceState,
+    isConnected: false,
+    isMuted: false,
+    isDeafened: false,
+    isSpeaking: false,
+    roomId: undefined,
+    serverId: undefined
+  };
+}
+
+function buildInactiveScreenShareState(user: User): User['screenShareState'] {
+  if (!user.screenShareState) {
+    return undefined;
+  }
+
+  return {
+    ...user.screenShareState,
+    isSharing: false,
+    streamId: undefined,
+    sourceId: undefined,
+    sourceName: undefined
+  };
+}
+
+function buildInactiveCameraState(user: User): User['cameraState'] {
+  if (!user.cameraState) {
+    return undefined;
+  }
+
+  return {
+    ...user.cameraState,
+    isEnabled: false
+  };
+}
+
+function buildPresenceAwareUser(existingUser: User | undefined, incomingUser: User): User {
+  const presenceServerIds = mergePresenceServerIds(existingUser?.presenceServerIds, incomingUser.presenceServerIds);
+  const isOnline = (presenceServerIds?.length ?? 0) > 0 || incomingUser.isOnline === true;
+  const status = isOnline
+    ? (incomingUser.status !== 'offline'
+      ? incomingUser.status
+      : (existingUser?.status && existingUser.status !== 'offline' ? existingUser.status : 'online'))
+    : 'offline';
+
+  return {
+    ...existingUser,
+    ...incomingUser,
+    presenceServerIds,
+    isOnline,
+    status
+  };
+}
+
+function buildPresenceRemovalChanges(
+  user: User,
+  update: { serverId?: string; serverIds?: readonly string[] }
+): Partial<User> {
+  const nextPresenceServerIds = update.serverIds !== undefined
+    ? normalizePresenceServerIds(update.serverIds)
+    : normalizePresenceServerIds((user.presenceServerIds ?? []).filter((serverId) => serverId !== update.serverId));
+  const isOnline = (nextPresenceServerIds?.length ?? 0) > 0;
+  const shouldClearLiveState = !isOnline
+    || (!!user.voiceState?.serverId && !nextPresenceServerIds?.includes(user.voiceState.serverId));
+
+  return {
+    presenceServerIds: nextPresenceServerIds,
+    isOnline,
+    status: isOnline ? (user.status !== 'offline' ? user.status : 'online') : 'offline',
+    voiceState: shouldClearLiveState ? buildDisconnectedVoiceState(user) : user.voiceState,
+    screenShareState: shouldClearLiveState ? buildInactiveScreenShareState(user) : user.screenShareState,
+    cameraState: shouldClearLiveState ? buildInactiveCameraState(user) : user.cameraState
+  };
+}
+
 export interface UsersState extends EntityState<User> {
   currentUserId: string | null;
   hostId: string | null;
@@ -86,11 +185,61 @@ export const usersReducer = createReducer(
     error
   })),
   on(UsersActions.userJoined, (state, { user }) =>
-    usersAdapter.upsertOne(user, state)
-  ),
-  on(UsersActions.userLeft, (state, { userId }) =>
-    usersAdapter.removeOne(userId, state)
+    usersAdapter.upsertOne(buildPresenceAwareUser(state.entities[user.id], user), state)
   ),
+  on(UsersActions.syncServerPresence, (state, { roomId, users }) => {
+    let nextState = state;
+
+    const seenUserIds = new Set<string>();
+
+    for (const user of users) {
+      seenUserIds.add(user.id);
+      nextState = usersAdapter.upsertOne(
+        buildPresenceAwareUser(nextState.entities[user.id], user),
+        nextState
+      );
+    }
+
+    const stalePresenceUpdates = Object.values(nextState.entities)
+      .filter((user): user is User =>
+        !!user
+        && user.id !== nextState.currentUserId
+        && user.presenceServerIds?.includes(roomId) === true
+        && !seenUserIds.has(user.id)
+      )
+      .map((user) => ({
+        id: user.id,
+        changes: buildPresenceRemovalChanges(user, { serverId: roomId })
+      }));
+
+    return stalePresenceUpdates.length > 0
+      ? usersAdapter.updateMany(stalePresenceUpdates, nextState)
+      : nextState;
+  }),
+  on(UsersActions.userLeft, (state, { userId, serverId, serverIds }) => {
+    const existingUser = state.entities[userId];
+
+    if (!existingUser) {
+      return (!serverId && !serverIds)
+        ? usersAdapter.removeOne(userId, state)
+        : state;
+    }
+
+    if (!serverId && !serverIds) {
+      return usersAdapter.removeOne(userId, state);
+    }
+
+    return usersAdapter.updateOne(
+      {
+        id: userId,
+        changes: buildPresenceRemovalChanges(existingUser, {
+          serverId,
+          serverIds
+        })
+      },
+      state
+    );
+  }),
   on(UsersActions.updateUser, (state, { userId, updates }) =>
     usersAdapter.updateOne(
       {
@@ -171,6 +320,8 @@ export const usersReducer = createReducer(
       isDeafened: false,
       isSpeaking: false
     };
+    const hasRoomId = Object.prototype.hasOwnProperty.call(voiceState, 'roomId');
+    const hasServerId = Object.prototype.hasOwnProperty.call(voiceState, 'serverId');
 
     return usersAdapter.updateOne(
       {
@@ -183,9 +334,8 @@ export const usersReducer = createReducer(
             isSpeaking: voiceState.isSpeaking ?? prev.isSpeaking,
             isMutedByAdmin: voiceState.isMutedByAdmin ?? prev.isMutedByAdmin,
             volume: voiceState.volume ?? prev.volume,
-            // Use explicit undefined check - if undefined is passed, clear the value
-            roomId: voiceState.roomId !== undefined ? voiceState.roomId : prev.roomId,
-            serverId: voiceState.serverId !== undefined ? voiceState.serverId : prev.serverId
+            roomId: hasRoomId ? voiceState.roomId : prev.roomId,
+            serverId: hasServerId ? voiceState.serverId : prev.serverId
           }
         }
       },