[MOD-3251] Stop heartbeats before sending the container snapshot RPC

modal/_container_io_manager.py

@@ -624,6 +624,9 @@ async def memory_snapshot(self) -> None:
         if self.checkpoint_id:
             logger.debug(f"Checkpoint ID: {self.checkpoint_id} (Memory Snapshot ID)")
 
+        # Heartbeats can leave the modal.sock file open, causing gVisor to crash
+        self.stop_heartbeat()
+
         await self._client.stub.ContainerCheckpoint(
             api_pb2.ContainerCheckpointRequest(checkpoint_id=self.checkpoint_id)
         )