Classify replacement EINVAL at the readlink syscall so the reader and importer
retain sibling observations. Give an admitted root's enumeration failure its
own typed field, use it for unresolved symlink coverage, and project it as a
graph limitation instead of an invalid dot-path child entry. Keep admission,
cancellation and cleanup failures distinct.
Closes#5135Closes#5136
BREAKING CHANGE: Partial reference-source reader results report failed root
enumeration in rootFailure instead of a failed directory child at path ".".
Historical source graphs preserve the root failure as a top-level limitation.
Continue validating child directories observed before a parent enumeration failure. Reconcile unobserved link targets at the reader using canonical path identity and the nearest failed ancestor, preserving exclusions and cancellation.
Refs: #4013, #4053, #4060
Co-authored-by: XY-code1 <1611761391@qq.com>
morluto