A mistyped --root (or running from another directory) was skipped silently,
so --check reported every documented name as stale.
Co-Authored-By: Claude Sonnet 5.5 <noreply@anthropic.com>
source_files compared every component of the absolute path against SKIP,
so a --root inside a directory named build or 3rdparty yielded no files.
Only components below the scan root are compared now.
Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>