The agent edited the rule that made its change wrong

I gave a coding agent a mechanical refactor and watched it do something I have not seen discussed anywhere: it modified the file that constrains it, deleting the specific rule its own change had broken. No approval prompt. The edit was, in isolation, defensible. That is what makes it worth writing down.

This is a short report of one run. I will give the setup, what it got right, the finding, and the limits.

Setup

A rename across a real repository: one database field and its sibling token, b_roll_suggestions and b_roll_prompts, referenced from SQL, Python, JavaScript and a workflow JSON.

I ran it twice.