sync/git(fix[update_repo]) Disambiguate rev-list for local refs matching paths

why: When a git repo has a local branch whose name matches a directory
(e.g. branch "notes" + directory "notes/"), git rev-list fails with
"fatal: ambiguous argument". The error was caught but not recorded in
SyncResult, so vcspull reported the sync as successful despite the
visible fatal error.

what:
- Check show_ref output for refs/heads/<tag> before calling rev-list
- Use fully-qualified refs/heads/ path when available, avoiding the
  ambiguity entirely (no fatal error emitted, no retry needed)
- Fall back to bare tag name when no refs/heads/ match exists (e.g.
  tags, SHAs, or refs not yet fetched)

Author: tony

src/libvcs/sync/git.py

@@ -467,10 +467,20 @@ def update_repo(
 
         # This will fail if the tag does not exist (it probably has not
         # been fetched yet).
+        #
+        # When the ref is local, use the fully-qualified refs/heads/ path
+        # if available to avoid ambiguity with paths (e.g. a branch named
+        # "notes" when a directory "notes/" also exists).
+        if is_remote_ref:
+            rev_list_commit = git_remote_name + "/" + git_tag
+        elif f"refs/heads/{git_tag}" in show_ref_output:
+            rev_list_commit = f"refs/heads/{git_tag}"
+        else:
+            rev_list_commit = git_tag
         try:
             error_code = 0
             tag_sha = self.cmd.rev_list(
-                commit=git_remote_name + "/" + git_tag if is_remote_ref else git_tag,
+                commit=rev_list_commit,
                 max_count=1,
             )