feat: rename 'reference path' to 'middle frame path'

Updates DEFAULTS, standard_keys, UI label, and timeline known_keys.
Adds _migrate_key_renames() called on load_json to auto-migrate
existing JSON files with the old key name.

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

tab_batch_ng.py

@@ -316,7 +316,7 @@ def render_batch_processor(state: AppState):
         'seed', 'cfg', 'camera', 'flf', KEY_SEQUENCE_NUMBER,
         'frame_to_skip', 'end_frame', 'transition', 'vace_length',
         'input_a_frames', 'input_b_frames', 'reference switch', 'vace schedule',
-        'reference path', 'video file path', 'reference image path', 'flf image path',
+        'middle frame path', 'video file path', 'reference image path', 'flf image path',
     }
     standard_keys.update(lora_keys)
 
@@ -632,7 +632,7 @@ def _render_sequence_card(i, seq, batch_list, data, file_path, state,
                 # Image paths with preview
                 for img_label, img_key in [
                     ('Reference Image Path', 'reference image path'),
-                    ('Reference Path', 'reference path'),
+                    ('Middle Frame Path', 'middle frame path'),
                     ('FLF Image Path', 'flf image path'),
                 ]:
                     with ui.row().classes('w-full items-center'):

tab_timeline_ng.py

@@ -618,7 +618,7 @@ def _render_preview_fields(item_data: dict):
     known_keys = {
         'sequence_number', 'general_prompt', 'general_negative', 'current_prompt', 'prompt',
         'negative', 'camera', 'flf', 'seed', 'resolutions',
-        'frame_to_skip', 'vace schedule', 'video file path',
+        'frame_to_skip', 'vace schedule', 'video file path', 'middle frame path',
     }
     # also skip lora keys
     custom_keys = [

utils.py

@@ -46,7 +46,7 @@ DEFAULTS = {
     "reference switch": 1,
     "video file path": "",
     "reference image path": "",
-    "reference path": "",
+    "middle frame path": "",
     "flf image path": "",
 
     # --- LoRAs (name as STRING, strength as FLOAT) ---
@@ -150,6 +150,15 @@ def save_snippets(snippets):
         json.dump(snippets, f, indent=4)
     os.replace(tmp, SNIPPETS_FILE)
 
+def _migrate_key_renames(data: dict) -> None:
+    """Rename legacy keys to their current names."""
+    for item in data.get(KEY_BATCH_DATA, []):
+        if not isinstance(item, dict):
+            continue
+        if 'reference path' in item and 'middle frame path' not in item:
+            item['middle frame path'] = item.pop('reference path')
+
+
 def _migrate_lora_keys(data: dict) -> None:
     """Split combined lora 'name:strength' into separate name and strength keys.
 
@@ -208,6 +217,7 @@ def load_json(path: str | Path) -> tuple[dict[str, Any], float]:
         with open(path, 'r') as f:
             data = json.load(f)
         t1 = time.time()
+        _migrate_key_renames(data)
         _migrate_lora_keys(data)
         t2 = time.time()
         mtime = path.stat().st_mtime