A stamp-shaped directory name is not ownership proof: pruneSkillBackups
counted and RemoveAll'd any 20260819-120000-shaped entry under
~/.dws/skill-backups, so a user or tool that created such a directory
lost its contents once DWS held five backups, and the Go backup path
(MkdirAll) adopted a same-named foreign root outright. The PowerShell
installers already implemented the correct contract; every other
surface now matches it.
Go stamps a freshly created root with the exact marker bytes the
install scripts write (.dws-skill-backup = "dws skill backup v1")
before any payload moves in, claims the root with mkdir so an existing
unproven root bumps to a collision suffix instead of being adopted,
and prunes only roots whose marker verifies — unmarked or wrongly
worded stamp-shaped directories are foreign data, preserved and never
counted against the keep limit. The shell installers (install.sh,
install-skills.sh, install-event.sh, install-devapp.sh) and the npm
installer apply the same rule in their backup collision loops, with
roots recorded as created by the running process exempt from marker
re-verification so a mid-run marker permission failure still reuses
this run's own root and keeps the sibling payload intact.
Regression tests cover every surface: pruning an unmarked/wrongly
marked stamp-shaped directory alongside marked ones, refusing to adopt
a foreign root (payload moves to a suffixed root, foreign data and its
nonexistent marker untouched), same-stamp reuse of a proven root, and
marker-write failure cleaning the empty fresh root.
copy_tree published staged children with mv, which replaces a
concurrently created same-name directory (POSIX rename succeeds over an
empty target) and whose rollback moved every dest child back — including
a concurrent writer's different-named entries — before deleting the
staging tree. Children now publish through kernel-level no-clobber
primitives (mkdir claim + recursion for directories with the recorded
mode restored, ln for regular files, ln -s for symlinks), a manifest
records exactly what this transaction published, the rollback retracts
only those entries in reverse order, and each level re-counts the
destination so a foreign different-named entry aborts the publish with
the destination retained. Read-only staged directories (0555 skill
trees) are made owner-writable for the move; the backup restore uses the
same discipline so a concurrent writer is refused without partially
draining the backup.
Regression tests cover both scripts: a concurrently created same-name
empty child directory and a different-named foreign entry mid-publish
are retained with the original backup kept; both fail against the
previous mv-based implementation.
柏智