#join

The operational recipe for shipping player-hosted (P2P) multiplayer in s&box (lobby mechanics, invite codes, the join handshake liveness contract, replication traps, and the three-rung testing ladder), covering the layer the official docs don't document and where live multi-peer sessions actually break.

A joining client's static join state (invite code, mode, attempt ID) gets wiped by the networked scene handoff: the bootstrap's OnEnabled resets statics before the join handshake uses them.

A published-build client join reloads the game assembly, wiping all statics. The reconstruct-not-reset fix from the scene-handoff case has nothing to reconstruct from unless join intent is persisted to disk.

On the host, spawning a joiner's character clobbers the host's own camera-target singleton because IsProxy is false at Components.Create time: re-resolve the claim at the first OnFixedUpdate.

The joiner's engine-side connect budget after entering a Steam lobby is a fixed ~3 seconds that game code cannot extend: any host-side delay exhausts it fast, so join recovery must be a fresh retry, never a longer wait.