every time my coding agent makes the same mistake twice, it goes through one loop now. walking through it with a real one from a small site I run..
Oct 21, 2026 · 4:25 PM UTC
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symptom first. a dialog's "PDF only" button just disappeared after an agent change. no error, build green, it simply wasn't there
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then root cause... the line that broke barely mattered.. the agent created a new css class called .skip, and a .skip class already existed that hides things. the actual bug was "it never checks if a class exists before inventing one"
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then pick the control. a guide (a line in CLAUDE.md) or a sensor (something that fails loudly). for this one a rule was enough: grep for the class name before creating a new one. small enough that it actually gets followed
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put it as early as you can. before the edit beats pre-commit, pre-commit beats CI, CI beats a user finding it a week later
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prove it works. put the mistake back on purpose and check the control catches it. if you never saw it fail you don't really know it works
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