The demo was clean. Forty-three test cases, all passing. The agent took a structured input, processed it, wrote the result downstream. I watched it run a dozen times in staging, everything right.
I put it live. Three days later, I found records in the database with dates in 1970.
What the demo hid
The test inputs had date fields formatted consistently. ISO 8601, clean strings, nothing unusual. In production, one upstream system sent dates in a different format. The agent read the field, made a plausible guess about what it meant, and wrote the result. No exception, no warning. Just a wrong date, written confidently, downstream at 3am with no one watching.
The failure mode was not dramatic. The agent did not hallucinate in the way people imagine. It treated an ambiguous input as an unambiguous one, picked the most likely interpretation, and was wrong. Exactly the kind of quiet, confident wrongness that is hard to catch because nothing breaks. The output looks fine. The data type is correct. The value is just from 1970.
