Closed-book card for day 49. This file is the interviewer. It is not a worked example.
Do not open the Phase 3 lessons while this timer is running. Do not scroll past the attempt barrier on the day 49 page. This is not the pastebin, and it is not a schema, index, or retention exercise.
Design warehouse inventory reservation.
A warehouse holds stock for many products. A buyer reserves units of a product so they can check out. Two buyers must not both walk away with the last unit. A reservation that is never finished does not last forever.
You have 35 minutes. Blank page. No notes.