Handle empty dataset repo in _list_existing_files

Catch the 404 EntryNotFoundError thrown when the repo has no commits yet
(data/ path does not exist on main), log it, and return [] so the first
commit can proceed normally.

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

logging_utils.py

@@ -86,11 +86,15 @@ def _make_path(now, uid):
 
 
 def _list_existing_files(api, repo_id):
-    return sorted(
-        f.path
-        for f in api.list_repo_tree(repo_id, repo_type="dataset", path_in_repo="data")
-        if f.path.endswith(".parquet")
-    )
+    try:
+        return sorted(
+            f.path
+            for f in api.list_repo_tree(repo_id, repo_type="dataset", path_in_repo="data")
+            if f.path.endswith(".parquet")
+        )
+    except Exception as e:
+        print(f"[log] could not list existing files (empty repo?): {e}")
+        return []
 
 
 def _build_add_ops(batch):