♻️(backend) extract notify_participant to util function

Move from lobby service to utils for reuse across services. Method is
generic enough for utility status. Future: create dedicated LiveKit
service to encapsulate all LiveKit-related utilities.

src/backend/core/utils.py

@@ -15,7 +15,15 @@ from django.core.files.storage import default_storage
 
 import aiohttp
 import botocore
-from livekit.api import AccessToken, LiveKitAPI, VideoGrants
+from asgiref.sync import async_to_sync
+from livekit.api import (  # pylint: disable=E0611
+    AccessToken,
+    ListRoomsRequest,
+    LiveKitAPI,
+    SendDataRequest,
+    TwirpError,
+    VideoGrants,
+)
 
 
 def generate_color(identity: str) -> str:
@@ -158,3 +166,37 @@ def create_livekit_client(custom_configuration=None):
     configuration = custom_configuration or settings.LIVEKIT_CONFIGURATION
 
     return LiveKitAPI(session=custom_session, **configuration)
+
+
+class NotificationError(Exception):
+    """Notification delivery to room participants fails."""
+
+
+@async_to_sync
+async def notify_participants(room_name: str, notification_data: dict):
+    """Send notification data to all participants in a LiveKit room."""
+
+    lkapi = create_livekit_client()
+
+    try:
+        room_response = await lkapi.room.list_rooms(
+            ListRoomsRequest(
+                names=[room_name],
+            )
+        )
+
+        # Check if the room exists
+        if not room_response.rooms:
+            return
+
+        await lkapi.room.send_data(
+            SendDataRequest(
+                room=room_name,
+                data=json.dumps(notification_data).encode("utf-8"),
+                kind="RELIABLE",
+            )
+        )
+    except TwirpError as e:
+        raise NotificationError("Failed to notify room participants") from e
+    finally:
+        await lkapi.aclose()