Every bookable thing (Cold Plunge #1, Sauna A, Cryo Chamber) is a Resource. Set capacity per vessel — a sauna that fits 6 stays open for six concurrent bookings; a solo cryo chamber sits at 1.
Add prep/cleanup buffer minutes so back-to-back bookings can't overlap the drain-and-refill window. Members book from the member app; walk-ins land in the desk queue.