# Build a multiplayer XR scene

Modify `main.js` so that:

1. The app joins a shared room called `"presence-demo"` when it starts.
2. Every remote user that's also in the room appears as a small sphere floating where their head is.
3. When a user leaves, their sphere disappears.

Keep the existing cylinder from the starter template. Use whatever local-dev transport makes sense for testing in a single browser opening two tabs.

Only edit `main.js`. Do not touch `index.html` or the importmap.