Challenge 1: Translate a Raw ws Broadcast to Socket.IO — Possible Solution
====================================================================

RAW ws (from Chapter 3):

  const clients = new Set();

  wss.on("connection", (socket) => {
    clients.add(socket);

    socket.on("message", (data) => {
      for (const client of clients) {
        if (client.readyState === client.OPEN) {
          client.send(data.toString());
        }
      }
    });

    socket.on("close", () => clients.delete(socket));
  });

SOCKET.IO EQUIVALENT:

  io.on("connection", (socket) => {
    socket.on("message", (data) => {
      io.emit("message", data); // broadcasts to every connected client
    });
  });

WHY THIS WORKS
--------------
- The entire "clients" Set, the manual .add()/.delete() bookkeeping, and
  the readyState-checked for-loop are ALL replaced by Socket.IO's own
  internal connection tracking — io.emit(...) already knows about every
  currently-connected client and only sends to ones that are actually
  still open, without the application needing to maintain that list
  itself.
- There's no separate "close" handler needed just to stop tracking a
  disconnected client for broadcast purposes — Socket.IO removes a
  disconnected client from its own internal registry automatically the
  moment the underlying connection closes.
- The Chapter 3 version deliberately broadcasts to EVERY client including
  the original sender (data.toString() sent back to the whole "clients"
  Set, which still contains the sender's own socket). io.emit(...)
  matches that same "send to everyone, including the sender" behavior —
  if the goal were "everyone except the sender," Socket.IO's
  socket.broadcast.emit(...) would be the correct equivalent instead.
- This side-by-side is exactly the trade this chapter describes: less
  code and less to get wrong, in exchange for being locked into
  Socket.IO's own client/server pairing rather than talking plain
  WebSocket.