clean-diff-guard

A generic "write clean code" review skill has been shown NOT to change agent behavior in kill-tests — it's too vague to act on. This guard replaces that with mechanically checkable imperatives about diff SCOPE, SIZE, and NOISE, not style taste. It exists because of a well-documented 2026 failure pattern: agents turning a 30-line task into 300 lines, touching files the task never mentioned, or sweeping a whole file/repo through a formatter because the diff was already open.

When to use — three modes