booking.sx: per-occurrence append-only stream, roster = replay. Booking
decided against an observed (roster, last-seq) snapshot, committed via
persist/append-expect — atomic check+append, no overbooking, no lock.
Explicit last-seat race test: two bookers, one booked, one conflict, roster
capped. Idempotent per actor. 97/97 green.
Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>
