Mock interview: stays booking and availability at Wanderstay

A full 50-minute model interview: Sara splits a 250-to-1 look-to-book system into a stale-but-fast search path and an exact booking path, claims all nights in one conditional update, survives a thundering herd and a payment timeout, rejects last-write-wins on channel updates, and turns overbooking into a measured 10× goal.