Use entry metadata to discover registration evidence independently of target
readability. Preserve failed metadata inspection as a named invalid diagnostic
instead of treating all lookup failures as absence. Remove the duplicate
boolean existence wrapper; configuration parsing remains the read owner.
Cover native permission-denied targets and metadata, dangling configuration
entries, maintenance exclusion, and public doctor output without mutation.
Validation: 73 focused tests across four files, check:fast, format:check,
and six isolated completed public doctor cost comparisons passed on macOS
arm64 / Node24.18.0. Native Windows/Linux permissions were not verified;
POSIX permission controls skip unsupported hosts and root.
Fixes#4905
morluto
d818c3d263