Keep save failure state and write timing with the canonical backing save, and
retain that identity on open files and mount aliases. Coordinate commits with
in-flight writes and file-size changes, preserve taint when recovery fails,
and mark the affected saves after a failed rename rollback.
Initialize shared write-injection settings with pthread_once so simultaneous
first writes do not race. Expand regressions for independent saves, aliases,
overlapping I/O and commits, failed recovery, and concurrent first writes.
Validation: 98 save regression checks, filesystem ThreadSanitizer, the full
host unit suite, and documentation checks pass.
Refs: https://github.com/seedds/nxnative/pull/288
Co-authored-by: Nishikori-Yui <165007678+Nishikori-Yui@users.noreply.github.com>
