reconciliation

A stateful pass over sorted events, which most candidates get working in ten minutes. The reason it is asked is the next ten: in this domain a false positive is a person accused of something.

The most common escalation in any data deployment, and the one that quietly ends trust in the platform. Four causes produce it, one of them means nobody is wrong, and you cannot tell them apart without running the ladder in order.

Every request emits a usage event worth real money, clients retry on timeouts, and tenants must be stopped at their quota and never overcharged. The hard parts are idempotent usage events and the succeeded-but-confirmation-lost case where the work happened but the client never heard back.