Senior Backend Engineer — growth-stage SaaS

Asked about delivery guarantees and duplicate-event volume before writing anything; explicitly narrowed scope to at-least-once delivery with idempotent consumers.

Proposed queue-backed ingestion with an outbox pattern; articulated the cost of exactly-once claims and chose verifiable idempotency instead. Compared Redis- vs DB-backed dedup with concrete failure scenarios.

Found both planted defects (a race on subscription-state update; a swallowed exception in the retry path) in 31 minutes, narrating hypotheses and eliminating them with logs rather than guesswork.

Used an assistant to draft the reconciliation query, then caught its incorrect join condition by testing against the seeded edge case before accepting it.

Handled clock-skew and out-of-order events when prompted, but did not raise them unprompted. Evaluator note: consistent once surfaced; recommend probing in the team interview.

Kept a running decision log unprompted; final walkthrough was ordered, complete, and honest about the shortcut taken on metrics emission.