feat(beaver): 完成Task Team功能v1实现，重构后端架构支持统一内核

新增内部Task系统，包括验证、反馈门控机制，实现自动质量验证
(通过率>=0.75)和用户反馈闭环(satisfied/revise/abandon)。

实现Agent Team v1协调器，支持sequence/parallel/dag执行策略，
sub-agent复用主AgentLoop，每个run使用独立memory snapshot。

建立Skill学习pipeline，包含draft/审核/发布/回滚完整生命周期，
通过Task验证通过且用户满意才生成学习候选。

重构目录结构，移除third_party依赖，建立统一engine内核，
所有agent共享运行时基础组件。

更新ContextBuilder清理provider消息字段，增强SkillContext版本管理，
集成TaskExecutionPlanner和TaskSkillResolver实现技能解析机制。

app-instance/backend/beaver/engine/session/store.py

@@ -432,6 +432,71 @@ class SessionStore:
         )
         return [MessageRecord.from_row(row) for row in rows]
 
+    def update_latest_assistant_event_payload(
+        self,
+        session_id: str,
+        run_id: str,
+        updates: dict[str, Any],
+    ) -> None:
+        """Merge payload fields into the latest visible assistant message for a run."""
+
+        if not updates:
+            return
+
+        def _do(conn: sqlite3.Connection) -> None:
+            row = conn.execute(
+                """
+                SELECT id, event_payload
+                FROM messages
+                WHERE session_id = ?
+                  AND run_id = ?
+                  AND role = 'assistant'
+                  AND event_type = 'assistant_message_added'
+                  AND context_visible = 1
+                ORDER BY timestamp DESC, id DESC
+                LIMIT 1
+                """,
+                (session_id, run_id),
+            ).fetchone()
+            if row is None:
+                return
+            payload: dict[str, Any] = {}
+            if row["event_payload"]:
+                try:
+                    parsed = json.loads(row["event_payload"])
+                    if isinstance(parsed, dict):
+                        payload = parsed
+                except json.JSONDecodeError:
+                    payload = {}
+            payload.update(updates)
+            conn.execute(
+                """
+                UPDATE messages
+                SET event_payload = ?
+                WHERE id = ?
+                """,
+                (json.dumps(payload, ensure_ascii=False, sort_keys=True), row["id"]),
+            )
+
+        self._execute_write(_do)
+
+    def set_run_context_visible(self, session_id: str, run_id: str, visible: bool) -> None:
+        """Set context visibility for all currently visible events in one run."""
+
+        def _do(conn: sqlite3.Connection) -> None:
+            conn.execute(
+                """
+                UPDATE messages
+                SET context_visible = ?
+                WHERE session_id = ?
+                  AND run_id = ?
+                  AND context_visible != ?
+                """,
+                (1 if visible else 0, session_id, run_id, 1 if visible else 0),
+            )
+
+        self._execute_write(_do)
+
     def get_messages_as_conversation(self, session_id: str) -> list[dict[str, Any]]:
         messages: list[dict[str, Any]] = []
         for record in self.get_event_records(session_id):