update slot resume pointers for step 503

slots/2/latest.json

@@ -1 +1 @@
-{"worker_id": "slot:2", "checkpoint": "slots/2/checkpoint-376", "step": 376, "updated_at": 1776359446}
+{"worker_id": "slot:2", "checkpoint": "slots/2/checkpoint-503", "step": 503, "updated_at": 1776388873}