A Friday review often begins with a polite subject line. The patch claims to fix a 504 on /invoice . Then the file list arrives: a new Redis helper, a line in requirements.txt , a port in docker-compose.yml , and a comment that the timeout was “probably a cache miss.” Nobody asked for a cache. The timeout lived in one function. The model widened the job because nothing in the repo told it where the fence was. This lab treats that leak as a teaching object, not a personality debate. AI codi...