The mkdir->rename->remove->rename directory fallback had a TOCTOU window
between the second remove and the second rename: a concurrent writer
creating an entry at the destination was silently clobbered. The fallback
now claims the destination once with mkdir and never unlinks it: the
fast-path rename publishes over the claim (Linux), and platforms that
refuse directory renames (macOS, Windows) move the staged children into
the claim through atomic no-clobber primitives (mkdir/os.Link/os.Symlink),
consuming the emptied source shell on success.
renameSkillPathNoReplace now returns the mkdir-claim identity captured by
the child-move path. PublishSkillPathNoReplace uses it as a three-state
ownership witness: the atomic/fast paths keep the staged-inode proof, the
child-move path proves dest is still the mkdir claim, and a mismatch
reports the new ErrSkillPathPublicationUncertain sentinel with the
destination retained. The witness is real on POSIX now: darwin and linux
report the dev:ino file identity instead of the empty no-op.
Upstream consumers honor the sentinel: the mono/multi upgrade copy
fallbacks no longer retry over an uncertain destination (the retry would
displace the concurrent writer's object), and skill setup reports the
retained destination instead of claiming a rollback.
Rewrites the fallback tests that pinned the removed remove-and-retry flow
and adds regression coverage: concurrent claim entries abort with the
destination retained, wholesale replacement after child-move reports the
uncertain sentinel, staged-set transactions pass the sentinel through,
and both copy fallbacks short-circuit (ablation-verified).
On Windows isNoReplaceRenameUnsupported always returns false, so the
fallback is never entered from the invalid-path test. Force the fallback
and swap skillPathLink to a non-EEXIST error to cover line 94 on all
platforms.
Add tests for mkdir non-EEXIST error, remove failure after rename
failure, first-rename-succeeds path (Linux behavior), retry-rename
path, and non-regular source safe-fail. All 24 changed executable
statements now covered on both macOS and Windows.
The fallback path for filesystems without RENAME_NOREPLACE/EXCL (NFS,
FUSE, overlayfs) used Lstat-then-Rename, which could overwrite a
concurrently created destination between the check and the rename.
Replace the TOCTOU-prone check with truly atomic no-clobber primitives:
- Directories: os.Mkdir atomically claims the destination (fails with
EEXIST if occupied). On Linux rename(2) replaces the empty dir
directly; on Darwin/Windows rename refuses existing dirs so the empty
dir is removed and the rename retried — any concurrent creation
between remove and rename is detected by the second rename failing.
- Files: os.Link atomically fails if the destination exists, then
os.Remove completes the move.
Add concurrent-creation test covering the mkdir→rename race window.
The !os.IsNotExist(statErr) branch in renameSkillPathNoReplace was
uncovered on Windows. Inject errNoReplaceRenameUnsupported for the
atomic rename and os.ErrPermission for skillPathLstat so the stat-error
path is exercised on every platform.
Restrict backup pruning to directories whose names match the DWS stamp
format (YYYYmmdd-HHMMSS with optional -N suffix) across all 8 installer
surfaces (Go, npm, 4 shell, 2 PowerShell). Unknown directories in
~/.dws/skill-backups are now preserved. Also fixes Windows coverage test
portability and covers the remaining macOS changed-code gap (retire
warning loop in runUpgrade).
A universal Agent whose obsolete private copy cannot be retired installs
nothing there, yet every entry point counted that retirement failure as an
install failure — aborting `npm install`, `dws skill setup`, and the shell
installers even when the canonical store and all links published correctly,
and skipping the skills-state write. Route retirement failures to a separate
warning path across all surfaces (Go upgrade + skill setup, npm, PowerShell,
install.sh, install-skills.sh, install-event.sh, install-devapp.sh).
Also:
- Add a checked-rename fallback for filesystems that reject the atomic
no-replace flag (NFS, FUSE, overlayfs); the no-clobber contract is kept and
the previously unsupported platforms build and work.
- PowerShell multi-mode links only bundle skills, never the shared canonical
store, so third-party/user skills are no longer fanned into every Agent root.
- Prune ~/.dws/skill-backups to the newest 5 on every surface; encode
HOME-relative backup names on PowerShell to preserve origin.
- Add simulated-win32 junction coverage and rewrite the tautological
no-replace test; remove dead code whose tests gave false coverage.
- Soften the overstated Windows ownership-proof comment (NTFS tunneling).
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