A skill is a directory with a SKILL.md; roots are ordered by priority (an
explicit path, then our own user directory, then the directories other
harnesses install into, with the project-scope one behind its own switch). The
first copy of a name wins and the ones it shadows stay listed for reporting
instead of vanishing.
The frontmatter reader covers the subset those files actually use — scalars,
booleans, ints, inline and block lists, | and > blocks, folded plain scalars —
so no YAML dependency is needed; a nested mapping is skipped and a structurally
broken block degrades to "no metadata" with a note, keeping a third-party skill
listable rather than dropping it. Metadata is cached against the directory list
and its SKILL.md timestamps, so a listing is cheap yet notices an edit.
NCBM