add assertion

src/petals/client/inference_session.py

@@ -331,6 +331,7 @@ class InferenceSession:
                         self._update_sequence(server_idx, block_idx, attempt_no)
 
                     server_session = self._server_sessions[server_idx]
+                    assert server_session.position == self.position
                     inputs = server_session.step(
                         inputs,
                         prompts[server_session.span.start : server_session.span.end],