bi-14 step 02 — Rung 2–3: a real fix with a regression test

Goal

Fix a behaviour bug in a subsystem you have already studied, with a test that fails first.

Check the directory is not being actively rewritten:

git log --since=90.days --oneline -- <directory> | wc -l

Reproduce it minimally. Write the failing test before the fix; confirm it fails on unpatched source.
Identify the correct layer. State why the fix belongs there and not at a call site — pre-empt the most likely objection in your CL description.
Fix. Run surrounding tests, not just yours.
Upload; handle review. If a reviewer proposes a design change you disagree with, ask what failure mode they are protecting against before arguing.
If the change is web-visible, expect a compatibility conversation and be ready to discuss usage data.