fix: persist UI history and retain recent L4 sessions

frontends/stapp.py

@@ -279,7 +279,8 @@ def render_main_stream(prompt=None):
             b = get_controller()
             b['obj'] = st.session_state.get('loop_prompt_input', ''); b['ready'] = False; b['ev'].set()
 
-if "messages" not in st.session_state: st.session_state.messages = []
+if not hasattr(agent, "_ui_messages"): agent._ui_messages = st.session_state.get("messages", [])
+if "messages" not in st.session_state: st.session_state.messages = agent._ui_messages
 for msg in st.session_state.messages:
     with st.chat_message(msg["role"]):
         # 用 slot=st.empty() + with slot.container(): ... 的外壳，DOM 路径和流式渲染完全一致，跨 rerun 对齐

memory/L4_raw_sessions/compress_session.py

@@ -156,6 +156,7 @@ def batch_process(src, l4_dir=None, dry_run=True):
     l4_dir = os.path.normpath(l4_dir or L4_DIR)
     raw_files = sorted(src) if isinstance(src, (list, tuple)) else \
                 sorted(glob.glob(os.path.join(src, 'model_responses_*.txt')))
+    raw_files = sorted(raw_files, key=os.path.getmtime)[:-10]  # always retain 10 newest raw files
     if not raw_files:
         print("No raw files found"); return {'processed': 0, 'skipped': 0, 'errors': 0, 'new_sessions': 0}