Every existing gate reads frontmatter with a regex or a line scan
(generate-docs.py, sync-codex-skills.py, check_paths.py), so a block that is
not valid YAML passed CI while Claude Code loaded the skill with no metadata.
The 14 files fixed in the previous commit had drifted that way unnoticed.
check_frontmatter.py parses each block with yaml.safe_load and enforces what
Claude Code actually reads:
errors - unparseable YAML, non-mapping frontmatter, missing description,
missing agent name, an agent name containing ':' (refused since
CC 2.1.218), or a missing frontmatter block
warnings - keys outside the current skill/agent frontmatter spec, and a
combined description + when_to_use over the 1536-char cap that
the skill listing truncates at
Warnings are non-blocking so this lands without requiring the wider metadata
cleanup; --strict flips them fatal. The run also tallies the off-spec keys no
runtime reads (license 172, metadata 125, domain 76, compatible_tools 37,
triggers 14), which gives that cleanup a worklist regenerated on every run.
Clean on the current tree: 593 files, 0 errors, 17 warnings.
Assisted-by: Claude Code:claude-opus-5
