Room-Based Architecture Requires Deterministic Room ID Generation

In a room-based multiplayer system, two users intending to join the same collaborative session end up in different rooms because the room ID is generated client-side with no coordination.

Derive the room ID from a canonical resource identifier (document ID, entity ID) rather than generating it randomly per session. The room ID is a function of what is being collaborated on, not of who is joining.

// Room ID derived from document — both users compute the same ID
function getRoomId(documentId: string, orgId: string): string {
  return `${orgId}:doc:${documentId}`;
}

// Server: join or create room
wss.on('connection', (ws, req) => {
  const { roomId, userId } = parseQuery(req.url);

  if (!rooms.has(roomId)) {
    rooms.set(roomId, new Set());
  }
  const room = rooms.get(roomId)!;
  room.add({ ws, userId });

  ws.on('close', () => {
    room.delete({ ws, userId });
    if (room.size === 0) rooms.delete(roomId);
  });
});

Rooms are a server-side routing mechanism for grouping connections. If the ID is random, users have no deterministic way to land in the same room. Deriving the ID from the shared resource makes it naturally consistent.