🚧(backend) update recording metadata alongside recording state changes

Previously, this was handled manually by the client, sending notifications to
other participants and keeping the recording state only in memory. There was no
shared or persisted state, so leaving and rejoining a meeting lost this
information. Delegating this responsibility solely to the client was a poor
choice.

The backend now owns this responsibility and relies on LiveKit webhooks to keep
room metadata in sync with the egress lifecycle.

This also reveals that the room.isRecording attribute does not update as fast
as the egress stop event, which is unexpected and should be investigated
further.

This will make state management working when several room’s owner will be in
the same meeting, which is expected to arrive any time soon.

src/backend/core/utils.py

@@ -25,6 +25,7 @@ from livekit.api import (  # pylint: disable=E0611
     LiveKitAPI,
     SendDataRequest,
     TwirpError,
+    UpdateRoomMetadataRequest,
     VideoGrants,
 )
 
@@ -244,6 +245,57 @@ async def notify_participants(room_name: str, notification_data: dict):
         await lkapi.aclose()
 
 
+class MetadataUpdateException(Exception):
+    """Room's metadata update fails."""
+
+
+@async_to_sync
+async def update_room_metadata(
+    room_name: str, metadata: dict, remove_keys: Optional[list[str]] = None
+):
+    """Update LiveKit room metadata by merging new values with existing metadata.
+
+    Args:
+        room_name: Name of the room to update
+        metadata: Dictionary of metadata key-values to add/update
+        remove_keys: Optional list of keys to remove from existing metadata.
+    """
+
+    lkapi = create_livekit_client()
+
+    try:
+        response = await lkapi.room.list_rooms(
+            ListRoomsRequest(
+                names=[room_name],
+            )
+        )
+
+        if not response.rooms:
+            return
+
+        room = response.rooms[0]
+
+        existing_metadata = json.loads(room.metadata) if room.metadata else {}
+
+        if remove_keys:
+            for key in remove_keys:
+                existing_metadata.pop(key, None)
+
+        updated_metadata = {**existing_metadata, **metadata}
+
+        await lkapi.room.update_room_metadata(
+            UpdateRoomMetadataRequest(
+                room=room_name, metadata=json.dumps(updated_metadata).encode("utf-8")
+            )
+        )
+    except TwirpError as e:
+        raise MetadataUpdateException(
+            f"Failed to update metadata for room {room_name}: {e}"
+        ) from e
+    finally:
+        await lkapi.aclose()
+
+
 ALPHANUMERIC_CHARSET = string.ascii_letters + string.digits