problem fix

app.py

@@ -6,7 +6,7 @@ import os
 import uuid
 from datetime import datetime
 from io import BytesIO
-from typing import Dict, List, Tuple
+from typing import Dict, List, Tuple, Optional
 
 import gradio as gr
 try:
@@ -139,7 +139,7 @@ def _read_existing_eval_keys(task_name: str) -> set:
     return keys
 
 
-def _schedule_round_robin_by_test_id(pairs: List[Dict[str, str]], seed: int | None = None) -> List[Dict[str, str]]:
+def _schedule_round_robin_by_test_id(pairs: List[Dict[str, str]], seed: Optional[int] = None) -> List[Dict[str, str]]:
     """Interleave pairs across test_ids for balanced coverage; shuffle within each group.
     """
     groups: Dict[str, List[Dict[str, str]]] = {}
@@ -248,7 +248,7 @@ def _append_local_persist_csv(task_name: str, row: Dict[str, object]) -> bool:
         return False
 
 
-def _upload_eval_record_to_dataset(task_name: str, row: Dict[str, object]) -> tuple[bool, str]:
+def _upload_eval_record_to_dataset(task_name: str, row: Dict[str, object]) -> Tuple[bool, str]:
     """Upload a single-eval JSONL record to a dataset repo.
     Repo is taken from EVAL_REPO_ID env or defaults to 'peiranli0930/VisEval'.
     Returns (ok, message) for UI feedback and debugging.
@@ -296,9 +296,10 @@ def on_task_change(task_name: str, _state_pairs: List[Dict[str, str]]):
     # Pick display order according to swap flag
     a_path = pair["model2_path"] if pair.get("swap") else pair["model1_path"]
     b_path = pair["model1_path"] if pair.get("swap") else pair["model2_path"]
+    max_index = max(0, len(pairs) - 1)
     return (
         pairs,
-        gr.update(value=0, minimum=0, maximum=len(pairs) - 1, visible=(len(pairs) > 1)),
+        gr.update(value=0, minimum=0, maximum=max_index, visible=(len(pairs) > 1)),
         gr.update(value=header),
         _resolve_image_path(pair["org_img"]),
         _resolve_image_path(a_path),