Given a production scenario, pick the right idiom: backoff, idempotency, bloom filters, leases. The senior-signal round.
These are the moves that separate an answer that works from one that survives production: retry policy, deduplication, admission control, coordination. Each answer explains the failure mode the technique exists to prevent. Cards are drawn with spaced repetition, so the ones you miss come back sooner and the ones you know back off. Progress is kept in your browser.