Function clone_dest_cleanable 

pub fn clone_dest_cleanable(dest: &Path) -> bool

R7 clone-cleanup: whether dest is safe to remove if a clone/git_clone about to run into it fails — either absent, or an already-empty directory. Compute this before running the clone, and pass the result to cleanup_failed_clone_dest on the error path — git/jj both refuse to clone into a non-empty existing directory, so if dest already had contents going in, a failure means that refusal, and the caller’s pre-existing data must never be deleted. Re-checking emptiness after the clone ran would be wrong: a failed clone can leave dest partially populated, so a post-hoc check could wrongly call a partial clone’s leftovers “empty” (or simply disagree with the pre-clone state).

Shared by vcs_git::clone_repo and vcs_jj::git_clone, which previously carried a byte-identical copy of this check plus its own best-effort remove_dir_all on the error path.