Every write mints a fresh server-side id; replaying an identical beacon produced two rows (live-verified). SQS consumer is explicitly at-least-once with no dedup. Fix: tracker-minted per-event UUID, derive sk from it, attribute_not_exists conditional put; same in the SQS consumer.
From the production-readiness audit (docs/research/production-readiness.md, eacf996). Verified with live probes where stated.