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/tests/unit/test_gateway_channels.py

@@ -45,6 +45,10 @@ class SlowService:
         return AgentService.build_outbound_message(inbound, result)
 
 
+class InvalidService:
+    is_running = True
+
+
 def test_gateway_routes_memory_channel_roundtrip() -> None:
     async def run() -> None:
         bus = MessageBus()
@@ -124,6 +128,23 @@ def test_gateway_rejects_channel_manager_and_channels_together() -> None:
     asyncio.run(run())
 
 
+def test_gateway_fails_fast_for_service_without_handle_inbound_message() -> None:
+    async def run() -> None:
+        try:
+            await run_gateway(
+                service=InvalidService(),
+                manage_service_lifecycle=False,
+                bus=MessageBus(),
+                stop_event=asyncio.Event(),
+            )
+        except TypeError as exc:
+            assert "handle_inbound_message" in str(exc)
+        else:
+            raise AssertionError("expected TypeError")
+
+    asyncio.run(run())
+
+
 def test_agent_service_maps_inbound_error_to_structured_outbound() -> None:
     async def run() -> None:
         service = AgentService()
@@ -144,6 +165,24 @@ def test_agent_service_maps_inbound_error_to_structured_outbound() -> None:
     asyncio.run(run())
 
 
+def test_agent_service_maps_stopped_runtime_to_stopped_outbound() -> None:
+    async def run() -> None:
+        service = AgentService()
+
+        async def stopped_submit_direct(message: str, **kwargs: Any) -> FakeResult:
+            raise RuntimeError("AgentLoop.submit_direct() is not accepting new tasks after stop()")
+
+        service.submit_direct = stopped_submit_direct  # type: ignore[method-assign]
+        outbound = await service.handle_inbound_message(
+            InboundMessage(channel="memory", content="hello", session_id="s1")
+        )
+
+        assert outbound.finish_reason == "stopped"
+        assert "not accepting new tasks" in outbound.metadata["error"]
+
+    asyncio.run(run())
+
+
 def test_channel_manager_start_cancellation_rolls_back_started_channels() -> None:
     class StartedChannel:
         name = "started"