A build check error in the area "The smoke run". An error: the game cannot be published until it is fixed.
The build check runs on every game LobbyLab builds, and each problem it finds has a stable code, the exact message, the file and line when it names one, and a link to this page.
What the check looks at
The check plays the game once: init, joins for minimumPlayers, the host's start, every smoke intent, then a view per player. Every call must return small plain JSON within its CPU budget (init and advance 25 ms, project 15 ms).
How to fix it
Accept member.join_requested while seats are free, with the display name from the payload.
Make each rulebook function total: accept unknown lifecycle events unchanged, reject bad intents with a short code instead of throwing, and return plain JSON (no undefined, NaN, classes or cycles).
See also: every error code, the API reference and the docs.