The Agent That Burned an Hour Re-Trying the Same 400 Error
An agent calls a tool. The tool returns 400 Bad Request with a perfectly structured error body: {"error": "missing required field", "field": "email"}. The agent's reasoning chain quotes the error back word for word, says "I need to include the email field," and then emits the next tool call with the exact same payload as before. The loop's retry policy, written years ago for a world of flaky HTTPS connections, treats the 400 as transient and fires it again. Three times. Eight. Fifteen. An hour later, the agent has burned through context, money, and a rate-limit budget without ever sending a request the tool could accept.
The failure looks like a model problem. It is not. The model read the error correctly. The harness around it never gave the correction anywhere to land.
