Why "UNIQUE(event_id)" Is the Double-Charge Defense Your Agent Rail Can't Skip FractalMesh / IronVision Nexus · son, real engineering, no buzzword theater Every payment integration — AI agent or otherwise — has one feature buyers actually verify before trusting it with money: can it charge me twice? Not "will it behave." Can it physically fail in the way that hurts people. The cloud-favorite answer is "webhooks are at-least-once delivery, so make your handler idempotent." Th...