The platform coverage gates execute only TestCrossPlatformCoverage-named
tests, so the child-move error and dispatch branches that the full local
suite covered incidentally were reported as uncovered changed code on
Windows (96.78% vs the 100% target). Adds a seam-driven edge suite for
the child-move fallback — source/claim/child stat and read failures,
per-child link and symlink collisions and publish failures, rollback
rename failure, foreign-entry abort, mode-restore failure, source shell
removal failure, nested-directory and simulated-symlink children, and
post-rename content drift — plus the retained-destination notice for a
dependent uncertain target in skill setup. The POSIX file identity impl
now consults the lstat seam so its degradation branches are coverable
the same way. Verified against the gate's own changed-line computation:
zero uncovered changed statements in internal/upgrade.
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).
玉澜