Fix page reset on save: async I/O and avoid needless deepcopy

Root cause: save_json + sync_to_db blocked the event loop while
serializing the growing history tree (all snapshots) as JSON,
causing NiceGUI websocket timeout and client reconnect.

- Skip history tree in snapshot deepcopy (copied only to discard)
- Move save_json/sync_to_db to asyncio.to_thread in all callbacks
- Make save_and_snap, commit, sort_by_number, shift_fts,
  _add_sequence, apply_mass_update async

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

tab_batch_ng.py

@@ -1,3 +1,4 @@
+import asyncio
 import copy
 import json
 import math
@@ -260,22 +261,22 @@ def render_batch_processor(state: AppState):
             src_file_select.on_value_change(lambda _: _update_src())
             _update_src()
 
-            def _add_sequence(new_item):
+            async def _add_sequence(new_item):
                 new_item[KEY_SEQUENCE_NUMBER] = max_main_seq_number(batch_list) + 1
                 for k in [KEY_PROMPT_HISTORY, KEY_HISTORY_TREE, 'note', 'loras']:
                     new_item.pop(k, None)
                 batch_list.append(new_item)
                 data[KEY_BATCH_DATA] = batch_list
-                save_json(file_path, data)
+                await asyncio.to_thread(save_json, file_path, data)
                 if state.db_enabled and state.current_project and state.db:
-                    sync_to_db(state.db, state.current_project, file_path, data)
+                    await asyncio.to_thread(sync_to_db, state.db, state.current_project, file_path, data)
                 render_sequence_list.refresh()
 
             with ui.row().classes('q-mt-sm'):
-                def add_empty():
+                async def add_empty():
-                    _add_sequence(copy.deepcopy(DEFAULTS))
+                    await _add_sequence(copy.deepcopy(DEFAULTS))
 
-                def add_from_source():
+                async def add_from_source():
                     item = copy.deepcopy(DEFAULTS)
                     src_batch = _src_cache['batch']
                     sel_idx = src_seq_select.value
@@ -283,7 +284,7 @@ def render_batch_processor(state: AppState):
                         item.update(copy.deepcopy(src_batch[int(sel_idx)]))
                     elif _src_cache['data']:
                         item.update(copy.deepcopy(_src_cache['data']))
-                    _add_sequence(item)
+                    await _add_sequence(item)
 
                 ui.button('Add Empty', icon='add', on_click=add_empty)
                 ui.button('From Source', icon='file_download', on_click=add_from_source)
@@ -300,12 +301,12 @@ def render_batch_processor(state: AppState):
     }
     standard_keys.update(lora_keys)
 
-    def sort_by_number():
+    async def sort_by_number():
         batch_list.sort(key=lambda s: int(s.get(KEY_SEQUENCE_NUMBER, 0)))
         data[KEY_BATCH_DATA] = batch_list
-        save_json(file_path, data)
+        await asyncio.to_thread(save_json, file_path, data)
         if state.db_enabled and state.current_project and state.db:
-            sync_to_db(state.db, state.current_project, file_path, data)
+            await asyncio.to_thread(sync_to_db, state.db, state.current_project, file_path, data)
         ui.notify('Sorted by sequence number!', type='positive')
         render_sequence_list.refresh()
 
@@ -335,12 +336,13 @@ def render_batch_processor(state: AppState):
             commit_input = ui.input('Change Note (Optional)',
                                     placeholder='e.g. Added sequence 3').classes('col')
 
-            def save_and_snap():
+            async def save_and_snap():
                 data[KEY_BATCH_DATA] = batch_list
                 tree_data = data.get(KEY_HISTORY_TREE, {})
                 htree = HistoryTree(tree_data)
-                snapshot_payload = copy.deepcopy(data)
+                # Only deepcopy the data we need (skip history tree — it's huge and gets discarded)
-                snapshot_payload.pop(KEY_HISTORY_TREE, None)
+                snapshot_payload = {k: copy.deepcopy(v) for k, v in data.items()
+                                    if k != KEY_HISTORY_TREE}
                 note = commit_input.value if commit_input.value else _auto_change_note(htree, batch_list)
                 try:
                     htree.commit(snapshot_payload, note=note)
@@ -348,9 +350,10 @@ def render_batch_processor(state: AppState):
                     ui.notify(f'Save failed: {e}', type='negative')
                     return
                 data[KEY_HISTORY_TREE] = htree.to_dict()
-                save_json(file_path, data)
+                # Run heavy I/O off the event loop to prevent websocket timeout
+                await asyncio.to_thread(save_json, file_path, data)
                 if state.db_enabled and state.current_project and state.db:
-                    sync_to_db(state.db, state.current_project, file_path, data)
+                    await asyncio.to_thread(sync_to_db, state.db, state.current_project, file_path, data)
                 state.restored_indicator = None
                 commit_input.set_value('')
                 ui.notify('Batch Saved & Snapshot Created!', type='positive')
@@ -365,11 +368,11 @@ def render_batch_processor(state: AppState):
 def _render_sequence_card(i, seq, batch_list, data, file_path, state,
                           src_cache, src_seq_select, standard_keys,
                           refresh_list):
-    def commit(message=None):
+    async def commit(message=None):
         data[KEY_BATCH_DATA] = batch_list
-        save_json(file_path, data)
+        await asyncio.to_thread(save_json, file_path, data)
         if state.db_enabled and state.current_project and state.db:
-            sync_to_db(state.db, state.current_project, file_path, data)
+            await asyncio.to_thread(sync_to_db, state.db, state.current_project, file_path, data)
         if message:
             ui.notify(message, type='positive')
         refresh_list.refresh()
@@ -647,7 +650,7 @@ def _render_vace_settings(i, seq, batch_list, data, file_path, state, refresh_li
 
                 _original_fts = _safe_int(seq.get('frame_to_skip', FRAME_TO_SKIP_DEFAULT), FRAME_TO_SKIP_DEFAULT)
 
-                def shift_fts(idx=i, orig=_original_fts):
+                async def shift_fts(idx=i, orig=_original_fts):
                     new_fts = _safe_int(fts_input.value, orig)
                     delta = new_fts - orig
                     if delta == 0:
@@ -659,9 +662,9 @@ def _render_vace_settings(i, seq, batch_list, data, file_path, state, refresh_li
                             batch_list[j].get('frame_to_skip', FRAME_TO_SKIP_DEFAULT), FRAME_TO_SKIP_DEFAULT) + delta
                         shifted += 1
                     data[KEY_BATCH_DATA] = batch_list
-                    save_json(file_path, data)
+                    await asyncio.to_thread(save_json, file_path, data)
                     if state.db_enabled and state.current_project and state.db:
-                        sync_to_db(state.db, state.current_project, file_path, data)
+                        await asyncio.to_thread(sync_to_db, state.db, state.current_project, file_path, data)
                     ui.notify(f'Shifted {shifted} sequences by {delta:+d}', type='positive')
                     refresh_list.refresh()
 
@@ -779,7 +782,7 @@ def _render_mass_update(batch_list, data, file_path, state: AppState, refresh_li
 
         select_all_cb.on_value_change(on_select_all)
 
-        def apply_mass_update():
+        async def apply_mass_update():
             src_idx = source_select.value
             if src_idx is None or src_idx >= len(batch_list):
                 ui.notify('Source sequence no longer exists', type='warning')
@@ -802,17 +805,17 @@ def _render_mass_update(batch_list, data, file_path, state: AppState, refresh_li
 
             data[KEY_BATCH_DATA] = batch_list
             htree = HistoryTree(data.get(KEY_HISTORY_TREE, {}))
-            snapshot = copy.deepcopy(data)
+            snapshot = {k: copy.deepcopy(v) for k, v in data.items()
-            snapshot.pop(KEY_HISTORY_TREE, None)
+                        if k != KEY_HISTORY_TREE}
             try:
                 htree.commit(snapshot, f"Mass update: {', '.join(selected_keys)}")
             except ValueError as e:
                 ui.notify(f'Mass update failed: {e}', type='negative')
                 return
             data[KEY_HISTORY_TREE] = htree.to_dict()
-            save_json(file_path, data)
+            await asyncio.to_thread(save_json, file_path, data)
             if state.db_enabled and state.current_project and state.db:
-                sync_to_db(state.db, state.current_project, file_path, data)
+                await asyncio.to_thread(sync_to_db, state.db, state.current_project, file_path, data)
             ui.notify(f'Updated {len(targets)} sequences', type='positive')
             if refresh_list:
                 refresh_list.refresh()