Build separate directory and authenticated-file indexes before applying
anatomy name preferences. Share those facts across application roots,
nested bundles, layout, metadata, executable candidates and signing paths.
Remove mixed child-name interpretation and downstream membership repairs.
A leaf Contents/Versions resource no longer changes a shallow layout, and
leaf files/symlinks cannot manufacture application roots. Real explicit
and implied directories retain their existing semantics and spelling.
Adapt the directory-identity proposal and source regressions from PR #3505
by @bnkaiteam, extending it to metadata file selection and root admission.
Validation: 57 focused checks, build, check:fast and docs:check pass.
30 tiny completed source projection cost controls preserve ordinary deep
and versioned replies byte for byte. No real-provider/target execution,
heavy profiling or published npm verification.
Fixes#3359Fixes#4779