Fix: handle empty index.json, fallback to zip scan

app/utils/data_loader.py

@@ -76,20 +76,25 @@ def load_prediction_index(pred_dir: str) -> pd.DataFrame:
             with zipfile.ZipFile(zip_path, 'r') as zf:
                 # Look for index.json inside the zip
                 idx_file = next((f for f in zf.namelist() if f.endswith("index.json")), None)
+                index_dict = {}
                 if idx_file:
                     with zf.open(idx_file) as f:
                         index_dict = json.load(f)
-                        for k, v in index_dict.items():
-                            rows.append({
-                                "name": k,
-                                "seq_len": v.get("seq_len", 0),
-                                "n_modes": v.get("n_modes", 0),
-                                "mean_disp_m0": v.get("mean_disp", 0.0),
-                                "max_disp_m0": v.get("max_disp", 0.0),
-                                "top_residue": -1,
-                            })
+
+                if index_dict:
+                    # Use pre-built index
+                    for k, v in index_dict.items():
+                        rows.append({
+                            "name": k,
+                            "seq_len": v.get("seq_len", 0),
+                            "n_modes": v.get("n_modes", 0),
+                            "mean_disp_m0": v.get("mean_disp", 0.0),
+                            "max_disp_m0": v.get("max_disp", 0.0),
+                            "top_residue": -1,
+                        })
                 else:
-                    # No index.json — scan zip for _mode_0.txt files
+                    # No index.json or empty — scan zip for _mode_0.txt files
+                    logger.info("index.json missing or empty — scanning zip for mode files...")
                     mode0_files = [f for f in zf.namelist() if f.endswith("_mode_0.txt")]
                     for mf in mode0_files:
                         base = os.path.basename(mf).replace("_mode_0.txt", "")