rollback, but leave a sanity check

src/client/sequential_autograd.py

@@ -191,6 +191,7 @@ async def sequential_backward(
 
     # For now, we do not support mixed dummy and grad prompts
     # Concat in num_layer dimension
+    assert not grad_prompts_reversed or len(grad_prompts_reversed) == len(prompts)
     grad_prompts = torch.cat(grad_prompts_reversed[::-1], dim=0) if grad_prompts_reversed else None
     return grad_outputs, grad_prompts