fix: 会话落库/加载缺 app context——后台线程 db 操作必须包 _flask_app.app_context()（历史加载与完成写回两处），否则静默失败（消息不落库、标题不生成）

web/agent_api.py

@@ -847,7 +847,9 @@ def _agent_thread(run_id, prompt, serial, cfg):
         # 历史来源：绑定了会话 → 从会话读（多轮上下文延续，DeepSeek 式）；
         # 无会话（CLI/兼容）→ 用运行态 history
         if conv_id:
-            msgs = _conv_msgs(conv_id)
+            # 后台线程需自行推 app context（与 _find_experiences 同思路）
+            with _flask_app.app_context():
+                msgs = _conv_msgs(conv_id)
             history = [{"role": m.get("role"), "content": m.get("content", "")[:4000]}
                        for m in (msgs or []) if m.get("role") in ("user", "assistant")]
             history = history[-24:]
@@ -886,16 +888,18 @@ def _agent_thread(run_id, prompt, serial, cfg):
             hist.append({"role": "user", "content": prompt[:2000]})
             hist.append({"role": "assistant", "content": (answer or "")[:4000]})
             _run["history"] = hist[-24:]
-        # 会话落库：本轮追加写回（新会话自动用首条消息作标题）
-        if conv_id:
+        # 会话落库：本轮追加写回（新会话自动用首条消息作标题）。
+        # 后台线程 db 访问需 app context。
+        if conv_id and _flask_app is not None:
             try:
-                saved = list(_run["history"])
-                title = None
-                if not db.session.execute(db.text(
-                        "SELECT title FROM agent_conversation WHERE id=:i"),
-                        {"i": conv_id}).scalar():
-                    title = "".join(prompt.split())[:30] or "新会话"
-                _conv_save_messages(conv_id, saved, title=title)
+                with _flask_app.app_context():
+                    saved = list(_run["history"])
+                    title = None
+                    if not db.session.execute(db.text(
+                            "SELECT title FROM agent_conversation WHERE id=:i"),
+                            {"i": conv_id}).scalar():
+                        title = "".join(prompt.split())[:30] or "新会话"
+                    _conv_save_messages(conv_id, saved, title=title)
                 _log.info(f"会话已保存: {conv_id}（{len(saved)} 条消息）")
             except Exception as e:
                 _log.warning(f"会话落库失败: {e}")