feat: 装配切换——main/服务构造线/conftest 迁至 Registry（含默认租户过渡兜底）

- main.py: 删全局 engine/async_session;lifespan 装配 TenantRegistry
  (seed_profiles → 仓库根 tenants/,路径锚定),预热默认租户 jiancai 挂
  app.state.default_runtime,逐 active 租户(库文件已存在)跑
  sweep_stale_pending,退出 dispose_all。app.state.registry 预置即沿用
  (测试注入缝)
- routes/runtime.py(过渡,Task 7 删): get_runtime——state.tenant 优先,
  缺省落 default_runtime;chat.py/chat_rest.py 全部改走它,消除
  main↔routes 循环依赖
- ConversationManager 构造线: 新增 runtime 可选参(持 session_factory/
  compiled_wall/config 引用;prompts 仍模块级,Task 6;业务接线 Task 9),
  fire_pending_pushes 随任务传 session_factory(后台写回派发租户的库)
- lead_push_service: 去 app.main import;写库入口显式收 session_factory,
  模块级 async_session=None 仅作测试注入兜底
- conftest: client 夹具 = 每测试独立 Registry(tmp data_dir)+ 真实
  lifespan 在 TestClient 循环内预热;删 _dispose_main_engine;
  async_db 保持 NullPool(跨 asyncio.run 循环安全,刻意不换 Registry 引擎)
- 测试仅动夹具/桩签名(断言零改动): wiring 桩补 session_factory 形参;
  history-404 用例改经真实 WS 路由造 widget 会话(引擎常驻连接绑定
  TestClient 循环,测试线程不得直开 session_factory)

Co-Authored-By: Claude Code <noreply@anthropic.com>

tests/test_chat_rest_session_history.py

@@ -1,4 +1,7 @@
-# `client` fixture from conftest (temp SQLite + overrides chat_rest.async_session).
+# `client` fixture from conftest (per-test Registry on tmp data_dir; default
+# tenant runtime pre-warmed by the app lifespan inside the TestClient loop).
+
+import json
 
 
 def test_session_creates_new(client):
@@ -26,17 +29,10 @@ def test_history_404_unknown_sid(client):
 
 def test_history_rejects_non_app_session(client):
     # widget-source conversations are not readable via this public endpoint
-    # (narrow the read surface to app only).
-    import asyncio
-    from app.engine.routes import chat_rest
-    from app.engine.services.conversation import ConversationManager
-    from app.engine.models import ConversationSource
-
-    async def _make_widget():
-        async with chat_rest.async_session() as db:
-            mgr = ConversationManager(db)
-            c = await mgr.create_conversation(source=ConversationSource.widget)
-            return c.session_id
-
-    sid = asyncio.run(_make_widget())
+    # (narrow the read surface to app only). 经真实 WS 路由造 widget 会话:
+    # 租户 engine 的常驻连接绑定 TestClient 的事件循环,测试线程不得另起
+    # asyncio.run 直开其 session_factory(跨循环复用会死锁)。
+    with client.websocket_connect("/ws/chat") as ws:
+        ws.send_text(json.dumps({"source": "widget"}))
+        sid = ws.receive_json()["session_id"]
     assert client.get(f"/api/chat/{sid}/messages").status_code == 404