Your AI Agent Did Not Crash. It Just Started Making Things Up.

I think the most dangerous agent bugs are the ones that look completely normal. No error. No crash. No red screen. No stack trace. The agent replies. The format looks right. The answer sounds confident. Everyone moves on. Meanwhile it quietly stopped using its tools three days ago and has been hallucinating ever since. That is the bug. I have seen this again and again while building agents. A model update changes behavior behind the API. A framework update messes with tool calling. A checkpoint resumes with bad state. A subagent silently stops running.