Two follow-ups to the latest CR:
* push/sync uploads (`pushUploadFilePinned`): the PUT-time check pinned inode,
size, and mtime before dispatch but nothing rechecked the source after PUT
succeeded — only the root itself. An editor overwrite, truncate-rewrite, or
mmap-in-place during transfer would land a mixed old/new byte stream in OSS
and still be committed, corrupting the remote file in overwrite/local-wins.
Now stat the still-open handle again before `commit_upload`; any change in
inode/size/mtime aborts the commit. Post-PUT stat failures also abort.
* status root (`walkLocalTree`): `filepath.WalkDir` refuses to follow the root
when it is itself a directory symlink and reports it as a non-regular entry,
so the walker silently returned an empty local index and status flagged
every remote file as `new_remote`. Fail closed before the walk: the root
must be a real directory; symlinks and non-directories are rejected with a
clear message. A `statusRootLstat` seam keeps the rejection regressible on
platforms that cannot create directory symlinks (Windows without admin).
Both fixes come with `TestCrossPlatformCoverage*` regressions and take the
platform coverage gate from 99.9356% back to 100.0000% (1553 statements).
The Windows coverage gate reported changed-code coverage at 99.9360% because
drive_push.go:471-473 — the branch that surfaces an error passed to the
fs.WalkDir callback as its third argument — was not exercised. macOS runners
happen to exercise it via directory-lstat failures, Windows runners do not.
Add walk_callback_receives_error under
TestCrossPlatformCoverageDrivePushFinalWalkAndCommandGates, which swaps
walkPinnedLocalFS to invoke the callback with a non-nil err and asserts the
error is bubbled up unchanged.
Verified locally that the new subtest hits drive_push.go:471.17,473.4 with
count=1.
chichuan