Last lesson we built a room server. It hands out seats and creates one shared secret seed. The server works, but no one can reach it yet. There is no way in. You can't type a code, send a link to a friend, or turn "a server is running" into "I'm in seat 2." That missing piece is client code. It runs before the scene loads. You can't open a peer mesh until you know your own seat at the table.

All of that pre-scene work lives in one module, roomClient.ts. It is just plain functions. There is no System and no EventBus yet. The functions do one job. They figure out which seat a browser gets. Then they split that answer into the two inputs the networked scene needs.

Generate a room code

A room needs a short name. It should be easy to read aloud over the phone. generateRoomCode makes one. It is six letters, nothing more.

From the room client:

const ROOM_CODE_ALPHABET = 'ABCDEFGHIJKLMNOPQRSTUVWXYZ';
const ROOM_CODE_LENGTH = 6;

/**
 * A shareable room code: `ROOM_CODE_LENGTH` random letters. The randomness is
 * injectable (defaulting to `Math.random`) so a test gets a deterministic code.
 */
export function generateRoomCode(rand: () => number = Math.random): string {
  let code = '';
  for (let i = 0; i < ROOM_CODE_LENGTH; i++) {
    code += ROOM_CODE_ALPHABET[Math.floor(rand() * ROOM_CODE_ALPHABET.length)];
  }
  return code;
}

The randomness is an argument. It defaults to Math.random. A test can pass in its own value to get the same code every time. Call the function with no arguments and you get a string. Drop that string straight into the address bar:

const code = generateRoomCode();
// → 'ABCDEF'
history.replaceState(null, '', `?room=${code}`);
// the URL is now the invite — copy it, send it

The host makes the code once. Everyone else opens the link and reads ?room= back out of the URL. The code is the meeting point. It is the public handle that every browser POSTs to.