The POSIX shell installers staged shared Skill links and published them
with mv after an existence check; a file or symlink another process
created at the destination between the check and the move was silently
replaced, and the inode confirmation could not detect the loss. Publish
by creating each link directly at its destination instead — symlink(2)
refuses an occupied path with EEXIST, so the creation itself is the
atomic no-replace check. A directory that appears at the destination
turns ln -s into a container; the nested link is removed after an
identity check and the transaction rolls back, leaving the foreign
directory untouched. Applied to install.sh, install-skills.sh,
install-event.sh, and install-devapp.sh. Also covers the remaining
retraction branches of the Go shell-removal fallback so changed-code
coverage is complete. Regression tests inject a concurrent occupant at
the publish instant for regular-file and directory cases and assert the
foreign object and its contents stay completely unchanged.
玉澜
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