Function compose 

pub fn compose(
    skill: &str,
    own: &[(String, &'static [u8])],
    shared: &[SharedArtifact],
) -> Result<Vec<PackageFile>, PackageError>

Compose one package from a skill’s own files and the shared artifacts.

own holds paths relative to the skill directory. The package carries SKILL.md, each Markdown file directly under references/, and every shared artifact copied under references/. Anything else, and any name two sources claim, is an error: a package that silently kept one copy would ship a gate that no longer matches its source.

Errors

Returns the first PackageError the files carry.