Skill audit loop

Skills are prompts, and prompts fail quietly. A skill can look excellent and still be ignored half the time, or be followed exactly and still produce worse output than no skill at all. You cannot see either of those by reading the SKILL.md. You see them by running the skill against fixed tasks, comparing against a run without it, and reading what the agent actually did.

This skill runs that loop:

1. Collect cases — real sessions where the skill was used, plus a few constructed ones.
2. Write checks — before touching the skill. The checks are the specification.
3. Run the matrix — every case, every arm, several repetitions.
4. Read the evidence — pass rates, cost, and the trace of what the agent did.
5. Revise once, verify, keep or revert — one hypothesis per round, with the user's sign-off.

The loop is not optional at step 5. A revision that isn't re-measured is just another guess with more words in it.