Adds task cleanup on extension shutdown

Implements a mechanism to cancel pending background tasks
when the extension is stopped. This ensures proper cleanup and
prevents potential issues with lingering tasks.

__init__.py

@@ -19,11 +19,24 @@ castle_static_files = [
     }
 ]
 
+scheduled_tasks: list[asyncio.Task] = []
+
+
+def castle_stop():
+    """Clean up background tasks on extension shutdown"""
+    for task in scheduled_tasks:
+        try:
+            task.cancel()
+        except Exception as ex:
+            logger.warning(ex)
+
 
 def castle_start():
     """Initialize Castle extension background tasks"""
-    logger.info("Starting Castle accounting extension background tasks")
-    asyncio.create_task(wait_for_paid_invoices())
+    from lnbits.tasks import create_permanent_unique_task
+
+    task = create_permanent_unique_task("ext_castle", wait_for_paid_invoices)
+    scheduled_tasks.append(task)
 
 
-__all__ = ["castle_ext", "castle_static_files", "db", "castle_start"]
+__all__ = ["castle_ext", "castle_static_files", "db", "castle_start", "castle_stop"]