The bug that made me build a whole tool: my agent kept saying done when it did nothing

I spent way too long chasing a bug that turned out to be the core problem with agents doing real work. The model would say "done, sent the email / created the ticket", and nothing fired. No error, run looked green. found out when a user asked where their thing was. The thing that broke my brain: you can't fix it by asking the model. A confident model tells you it did something it never did, and if you ask, "Are you sure?" It just says yes again. You're asking the liar to confirm its own alibi. Re-prompting does nothing. So I stopped trusting what the agent says and started trusting receipts. Did a real tool call actually fire this turn, and did it return proof? No matching call in the trace means unknown, not done. same for a call that returns empty and gets treated as success. state advances on receipts, not narration. That idea turned into a small open-source thing I'm building. wild how much of "agent reliability" is just refusing to take the model's word that an action happened. Does anyone else building agents run into this? Curious how you're catching it, or if you've just been eating the silent failures like I was.