Refactor blocklist import registration to async startup flow

backend/app/tasks/blocklist_import.py

@@ -13,7 +13,6 @@ existing entry without creating duplicates.
 
 from __future__ import annotations
 
-import inspect
 from typing import TYPE_CHECKING, Any
 
 import structlog
@@ -76,7 +75,7 @@ async def _run_import(app: Any) -> None:
             await db.close()
 
 
-def register(app: FastAPI) -> None:
+async def register(app: FastAPI) -> None:
     """Add (or replace) the blocklist import job in the application scheduler.
 
     Reads the persisted :class:`~app.models.blocklist.ScheduleConfig` from
@@ -89,30 +88,14 @@ def register(app: FastAPI) -> None:
         app: The :class:`fastapi.FastAPI` application instance whose
             ``app.state.scheduler`` will receive the job.
     """
-    import asyncio  # noqa: PLC0415
-
-    async def _do_register() -> None:
-        db, close_db = await _get_db(app)
-        try:
-            config = await blocklist_service.get_schedule(db)
-        finally:
-            if close_db:
-                await db.close()
-        _apply_schedule(app, config)
-
-    # APScheduler is synchronous at registration time; use asyncio to read
-    # the stored schedule from the DB before registering.
-    coro = None
+    db, close_db = await _get_db(app)
     try:
-        loop = asyncio.get_event_loop()
-        coro = _do_register()
-        loop.run_until_complete(coro)
-    except RuntimeError:
-        # If the current thread already has a running loop (uvicorn), schedule
-        # the registration as a coroutine.
-        if coro is not None and inspect.getcoroutinestate(coro) != inspect.CORO_CLOSED:
-            coro.close()
-        asyncio.ensure_future(_do_register())
+        config = await blocklist_service.get_schedule(db)
+    finally:
+        if close_db:
+            await db.close()
+
+    _apply_schedule(app, config)
 
 
 def reschedule(app: FastAPI) -> None: