Idempotency

The property that repeating the same request produces the same result as sending it once, so retries can't double-count.

Idempotency is the property that making the same request multiple times has the same effect as making it once. It matters wherever delivery is "at-least-once" rather than "exactly-once": retries, offline queues, and double-fired pixels all mean the same event can arrive more than once, and without idempotency each arrival would count as a separate conversion.

TraqLyte enforces this by deduping outcomes on (assignment_id, dedupe_key): the caller supplies a key that identifies the specific event, and a repeat with the same key is silently absorbed rather than recorded twice. See at-least-once delivery, or why your conversion counts are wrong for the full design.

The dedupe key is caller-supplied rather than server-generated, because only the system emitting the event actually knows which upstream occurrence produced it. A server-assigned key could dedupe delivery attempts, but has no way to recognize that two different-looking requests describe the same real-world conversion.