fix offline inference chat response prompt (#32088)

Signed-off-by: Andy Xie <andy.xning@gmail.com>

examples/offline_inference/context_extension.py

@@ -9,7 +9,7 @@ Usage:
     python examples/offline_inference/context_extension.py
 """
 
-from vllm import LLM, SamplingParams
+from vllm import LLM, RequestOutput, SamplingParams
 
 
 def create_llm():
@@ -45,13 +45,15 @@ def run_llm_chat(llm):
         {"role": "assistant", "content": "Hello! How can I assist you today?"},
     ]
     outputs = llm.chat(conversation, sampling_params, use_tqdm=False)
-    return outputs
+    return outputs, [
+        conversation,
+    ]
 
 
-def print_outputs(outputs):
+def print_outputs(outputs: list[RequestOutput], conversations: list):
     print("\nGenerated Outputs:\n" + "-" * 80)
-    for output in outputs:
-        prompt = output.prompt
+    for i, output in enumerate(outputs):
+        prompt = conversations[i]
         generated_text = output.outputs[0].text
         print(f"Prompt: {prompt!r}\n")
         print(f"Generated text: {generated_text!r}")
@@ -60,8 +62,8 @@ def print_outputs(outputs):
 
 def main():
     llm = create_llm()
-    outputs = run_llm_chat(llm)
-    print_outputs(outputs)
+    outputs, conversations = run_llm_chat(llm)
+    print_outputs(outputs, conversations)
 
 
 if __name__ == "__main__":