feat(backend): 完善 Workflow 与 DeepResearch 的运行链路与持久化能力

功能说明：\n- 重构并增强工作流网关执行链路，支持更完整的 proposal 与 run 调度参数透传\n- 增加 DeepResearch/workflow 运行事件持久化能力并补齐建表 SQL 与查询/保存接口适配\n- 优化 lead agent 与 deep research runner 的中间态处理，增强线程收集与执行链并发控制\n- 调整工作流执行器与任务路由，提升兼容性并完善错误与回放行为\n- 补充回归测试：deep_research 持久化、workflow 并发、定义加载、引擎执行、run 流程等覆盖

offline-backend-20260512/backend/tests/test_workflow_concurrency.py

@@ -322,6 +322,34 @@ async def test_sql_append_without_run_row_falls_back_to_max_seq(session_factory)
     assert (first["seq"], second["seq"]) == (1, 2)
 
 
+@pytest.mark.asyncio
+async def test_sql_event_replay_keeps_full_native_message_frame(session_factory) -> None:
+    """A reconnect must receive the same large DeerFlow tool frame as live SSE."""
+    events = SqlWorkflowEventStore(session_factory)
+    run_id = f"run-{uuid.uuid4().hex[:8]}"
+    payload = {
+        "messages": [
+            {
+                "type": "tool",
+                "name": "web_search",
+                "content": {"results": [{"snippet": "x" * 90_000}]},
+            },
+            {"langgraph_node": "research"},
+        ]
+    }
+
+    await events.append(
+        run_id=run_id,
+        workflow_id="wf-1",
+        version_id="v-1",
+        event_type="node.message",
+        payload=payload,
+    )
+
+    replayed = await events.list_after(run_id)
+    assert replayed[0]["payload"] == payload
+
+
 # ── sink: persist-then-publish, never ghost events ──────────────────────