4a - the detection floor. A shadowed install now reports which triggers are
shadowed and which scope wins, at install time and through a new W028
/gsd-health diagnostic. Exit codes are untouched: a shadowed install is a
warning, not a failure. Only triggers whose stem exists at BOTH scopes are
reported, so a global full profile beside a local core profile no longer
names local artifacts the user does not have.
4b - spec-root reachability, claude runtime and global scope only. The
winning global skill stops carrying a static workflow @-include and instead
resolves its spec at runtime: prefer the project-local copy, fall back to
the global one, stop if neither exists. Every other @-include stays static,
and the local emission is byte-identical. It runs after the staged-skills
rewrite pass, whose claude branch would otherwise mangle the literal tilde
path into an undocumented $HOME form.
Also fixed inline: readInstallManifest classified a top-level JSON array as
an installed v1 manifest, because typeof [] is object.
Refs #2873
2641e6cb67