design:modify — Spec-Aware Design Changes with Safety Checks

What This Skill Does

Given a FAIL item from a design:review output (or a direct change request from Tyler), modifies design_spec.py safely:

1. Constraint simulation — compute all 4 aisle clearances BEFORE writing any file
2. Feasibility check — reject changes that resolve one FAIL but introduce another
3. Safe spec editor — validate Python syntax and import before applying
4. Pipeline runner — execute pixi run permit-docs, detect silent failures
5. Diff reporter — show what changed in spec and which PDFs were regenerated

Never writes to design_spec.py without passing all safety checks.

Prerequisites