A lobby should survive its host disappearing without asking every client to guess what happened. The least complex design that does that is a server-owned host lease, a deterministic successor rule, and a replayable event log. Express exposes commands and backfill; the authoritative transition belongs in one serialized state change.

Choice Reconnect behavior Backfill behavior Main risk

Immediate reassignment Return as a member Replay after the last sequence Brief loss causes host churn

Lease, then successor Resume during the lease Replay the committed suffix Handoff waits for expiry

Client election Peers negotiate Peers may hold different gaps Split-brain authority

Recommendation: use a short server-side lease and choose the next host from an ordering the server owns. Persist the transition before broadcasting it.…