On Windows, os.symlink() raises OSError (WinError 1314) unless the
process has Administrator rights or Developer Mode is enabled. The SSH
bulk-upload staging logic used symlinks to mirror the remote layout
before piping through tar; this caused all ssh_bulk_upload tests to
fail on Windows.
- ssh.py: wrap os.symlink() in try/except OSError and fall back to
shutil.copy2() so staging works on every platform. shutil was already
imported, no new dependency introduced.
- file_sync.py: replace str(Path(remote).parent) with
posixpath.dirname(remote) in unique_parent_dirs(). pathlib.Path uses
the host separator (\ on Windows), but these paths are sent to a
remote Linux host over SSH and must always use forward slashes.
- test_ssh_bulk_upload.py: make test_staging_symlinks_mirror_remote_layout
platform-agnostic — assert file existence and content instead of
os.path.islink() + os.readlink(), since the staged entry may be a
copy on Windows.
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