# US-03 — Ready up and start from the lobby

**As a** host,
**I want to** pick the level and start once everyone is ready,
**so that** the group begins together on the same kitchen.

## Acceptance criteria
1. The lobby lists every seat: name, ready state, host crown, connection state.
2. Any player can toggle *Ready*; the host can pick any **unlocked** level from a
   list showing name, target score, time limit, and difficulty pips.
3. *Start* is enabled for the host when ≥ 1 non-host player is ready (or the host is
   alone — solo play is allowed).
4. Starting begins a 3-2-1 `countdown` shown identically on all clients, then the
   first `snap` arrives.
5. Non-host players cannot start or change level; the attempt shows a disabled control
   (no console errors, no silent failure).
6. If the host leaves in `LOBBY`, host status transfers to the lowest occupied seat;
   in `PLAYING` the round continues.
7. Someone leaving during `COUNTDOWN` cancels the countdown back to `LOBBY`.
8. Starting creates a round record in the in-memory session store.

## E2E suite
`tests/e2e/test_us03_ready_and_start.py` — two contexts: ready toggles visible to
both, non-host start rejected, countdown then both screens show the kitchen.

## Phases
`05_anonymous_lobbies_and_room_lifecycle`, `06_realtime_websocket_protocol`,
`07_canvas_client_and_hud`