- quarter_target_w() is now the margin under quarter_ceiling_w(): a peak
banked between cap - margin and the cap was aimed at exactly, so one
overshoot crossed the cap; above the cap the same overshoot raised the bill.
- safety79_identity.py hashes charge_headroom_w() and the shaping suspension,
and adds n1_maint/n2_maint (cheap window, forecast across cap - 50 .. cap).
Digests re-printed on ed739d4 and pinned; margin 0 still identical.
- test_margin_under_banked_peak; DECISIONS and DOCS updated.
Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>