Your Agent Patch's Tests Never Touched the Changed Lines: A Diff-Coverage Gate
A green suite after an agent patch tells you one thing: nothing you ran crashed. It does not tell you that anything you ran executed the lines that changed. Those two statements only connect when some test actually enters the new code — and with agent patches, that connection is precisely what breaks. Diff coverage closes the gap cheaply. Intersect the patch's changed lines with the lines the suite executed, per hunk, and refuse to merge hunks that nobody ran. Below is a working gate for that,…