refactor: govern background tasks and query ownership

app/api/dependencies/subscription.py

@@ -2,7 +2,7 @@
 
 from typing import Any, cast
 
-from fastapi import BackgroundTasks, Depends
+from fastapi import Depends
 from sqlalchemy.ext.asyncio import AsyncSession
 from sqlalchemy.orm import Session
 
@@ -38,6 +38,8 @@ from app.runtime.events import eventmanager
 from app.runtime.log import logger
 from app.schemas.types import EventType
 from app.startup.context import HostRuntime
+from app.api.context import get_background_task_registry, resolve_background_task_registry
+from app.runtime.tasks import TaskRegistry
 
 
 async def _publish_subscribe_deleted(
@@ -94,14 +96,14 @@ def get_delete_subscriptions_by_identity_command(
 
 
 def get_search_subscriptions_command(
-    background_tasks: BackgroundTasks,
+    task_registry: TaskRegistry = Depends(get_background_task_registry),
     db: AsyncSession = Depends(get_async_session),
     runtime: HostRuntime = Depends(get_host_runtime),
 ) -> SearchSubscriptionsCommand:
     """组装手工订阅搜索用例，并把调度延迟到响应后的后台任务。"""
     def schedule_search(subscribe_id: int | None, state: str | None) -> None:
         """按历史参数提交订阅搜索调度任务。"""
-        background_tasks.add_task(
+        resolve_background_task_registry(task_registry).create_sync(
             start_scheduler_job,
             job_id="subscribe_search",
             sid=subscribe_id,