M2b：删除旧 chat 体系——线性会话/叩心/情绪/纪念日模型与页面退役（迁移 003 双向验证），runs 去会话外键，测试全量修剪

backend/tests/test_runtime_limits.py

@@ -30,7 +30,7 @@ async def test_event_payload_limit(monkeypatch: pytest.MonkeyPatch) -> None:
     character_id = await _admin_character_id()
     async with AsyncSessionLocal() as db:
         run = await create_run(
-            db, character_id=character_id, session_id=None, model_hint="default-chat"
+            db, character_id=character_id, model_hint="default-chat"
         )
         with pytest.raises(AppError) as exc:
             await append_event(
@@ -49,7 +49,7 @@ async def test_run_max_events(monkeypatch: pytest.MonkeyPatch) -> None:
     character_id = await _admin_character_id()
     async with AsyncSessionLocal() as db:
         run = await create_run(
-            db, character_id=character_id, session_id=None, model_hint="default-chat"
+            db, character_id=character_id, model_hint="default-chat"
         )
         await append_event(
             db, run_id=run.id, character_id=character_id, event_type="message.delta", payload={}
@@ -70,7 +70,7 @@ async def test_cancel_run() -> None:
     character_id = await _admin_character_id()
     async with AsyncSessionLocal() as db:
         run = await create_run(
-            db, character_id=character_id, session_id=None, model_hint="default-chat"
+            db, character_id=character_id, model_hint="default-chat"
         )
         await db.commit()
     response = await cancel_run(run.id)