Enforce HARDEN moratorium with a tripwire, not a vibe

[chokevin]

Surfaced by

2026-04-19 retro (see RETROS.md).

The problem

docs/reckons/kstack-itself-20260418.md declared HARDEN with explicit non-goal: no new skills until 5 retros worth of dogfood evidence. In the same session we shipped two new skills (/airun-triage, /research). Each had a documented justification — but the constraint never actually bit. A decision the system can't enforce is a wish.

Options

1. PR template checkbox + reviewer waiver.
2. CONTRIBUTING.md gate — new-skill PRs must reference N entries in dogfood-log.md.
3. dogfood-log.md at repo root — append-only, retros write to it, new-skill PRs link the entries that justify the addition.
4. Pre-commit hook (over-engineered at N=8).

Recommendation

#3 + #1. Skip #4 for now.

Acceptance

HARDEN moratorium re-checkable mechanically (count entries in dogfood-log.md), not vibes.