An AI agent ingests a customer ticket, queries three internal APIs, looks up a record in a database, drafts a response, and hands it off to a human reviewer. Every individual call returns a 200. The unit tests pass. The integration tests pass. The response gets approved.A week later, the support team notices the agent has been quietly recommending the wrong refund tier for one product category — for nine days. Nothing crashed. Nothing logged an error. The system did exactly what its tests said it should do.