Frontmatter Guard Skill

Convention: see skills/conventions/quality.md for citation rules; this skill is structural validation, not citation auditing.

Contract

This skill guarantees:

• Every brain page is scanned against the eight canonical frontmatter validation classes
• Mechanical errors (nested quotes, missing closing ---, null bytes, slug mismatch) are auto-repairable on demand with .bak backups
• Validation logic is shared with gbrain doctor's frontmatter_integrity subcheck — single source of truth
• Reports per source (gbrain is multi-source since v0.18.0); never silently audits the wrong root

Why This Exists