Closed-book card for day 88. This file is the interviewer. It is not a worked example.
Do not open the metrics ingestion or metrics query lessons while this timer is running. Do not scroll past the attempt barrier on the day 88 page. This is not a dashboard day and not a payments ledger.
Design an event intake system.
Many producers send events. The system must accept them at high write rates, avoid treating retries as new facts, deal with events that arrive late, and land them in a durable sink downstream consumers can trust.
You have 35 minutes. Blank page. No notes.