Nine tests fail on an ordinary Windows machine, eight in backend/local and
TestEnvironmentVariables in cmdtest, all with
symlink file.txt \?\C:\Users\...\symlink.txt: A required privilege is not
held by the client.
Windows grants SeCreateSymbolicLinkPrivilege only to an elevated process or one
running with Developer Mode enabled, and a default install gives an ordinary
user neither. CI does not see this because the windows-latest runner is
elevated, so the failures only show up on a contributor's own machine, where
AGENTS.md asks for make quicktest to pass before opening a pull request.
cmdtest already recognised the situation and attached a note to the failure
saying the test could safely be ignored. If it is safe to ignore then the test
knows it cannot run, so skip it and say why instead.
backend/local gains a helper that tries a symlink in t.TempDir() and skips if it
cannot make one, called from the six tests that need the privilege. Where a
platform can create symlinks the probe succeeds and nothing is skipped, so other
platforms are unchanged.
TestMetadata is skipped whole because it creates its symlink before anything
else and the object built from it is used throughout.
TestSymlinkEscapeConcurrent is left alone: it goes through putLink and ignores
the error, so it never needed the privilege.
