Replace the charCount * fontSize * 0.55 text sizing heuristic with canvas-based measurement (graceful fallback when native deps unavailable). Add validate.mjs for automated spatial checks (text overflow, arrow-text collisions, element overlap). Update element format reference with sizing rules, label guidelines, and arrow routing conventions. Add verification step to SKILL.md workflow. Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>