matbanik

Published August 06, 2026 on matbanik.info A reviewer looked at my code and found a bug. One route returned a 500 error when it should have returned a 404. It reported the finding, clearly, with the file and the line. My agent fixed that route. Exactly that one. Five other routes had the identical bug. They sat there, untouched, while the agent reported the work complete — and it wasn't lying. It had fixed the thing it was shown. It just never thought to ask how many other places the same mistake was hiding. I spent a while assuming this was a model problem, and that a better model would fix it. That turned out to be wrong, and the fix that worked was dumber than I expected. AI coding agent guardrails are not about making the model smarter. They're about giving it somewhere to put things down. Every drawer in that cabinet is something the agent would otherwise have to keep in its head. Where AI coding agents quietly go wrong The failures that cost me the m...