fix(guardrails): keep the assistant turn when scoping empties the request history

A request whose turns all fall outside the guardrail's scope, such as a user-only
request under scan_only_tool_results, still supplied a conversation, so the response
scan now carries the reply as the sole assistant turn instead of dropping
structured_messages. Response-only behavior stays when no conversation was supplied

Co-Authored-By: Devin AI <158243242+devin-ai-integration[bot]@users.noreply.github.com>

litellm/llms/base_llm/guardrail_translation/base_translation.py

@@ -30,6 +30,7 @@ class RequestScanContext:
 
     structured_messages: tuple["AllMessageValues", ...] = ()
     tools: tuple["ChatCompletionToolParam", ...] = ()
+    conversation_supplied: bool = False
 
     @staticmethod
     def scoped(
@@ -51,6 +52,7 @@ class RequestScanContext:
         return RequestScanContext(
             structured_messages=tuple(structured_messages[index] for index in scoped_indices),
             tools=() if scan_only_tool_results else tuple(tools),
+            conversation_supplied=bool(structured_messages),
         )
 
 
@@ -308,7 +310,7 @@ class BaseTranslation(ABC):
         if request_data is None:
             return inputs
         context: Final = self.request_scan_context(request_data, guardrail_to_apply)
-        if not context.structured_messages:
+        if not context.conversation_supplied:
             return inputs
         assistant_turn: Final = response_assistant_turn(inputs.get("texts") or (), inputs.get("tool_calls") or ())
         contextual_inputs: Final[GenericGuardrailAPIInputs] = {

litellm/llms/openai/responses/guardrail_translation/handler.py

@@ -454,8 +454,9 @@ class OpenAIResponsesHandler(BaseTranslation):
 
     def request_scan_context(self, data: dict, guardrail_to_apply: "CustomGuardrail") -> RequestScanContext:
         raw_tools: Final = data.get("tools")
+        structured_messages: Final = tuple(self.get_structured_messages(data) or ())
         return RequestScanContext(
-            structured_messages=tuple(self.get_structured_messages(data) or ()),
+            structured_messages=structured_messages,
             tools=tuple(
                 cast(ChatCompletionToolParam, tool)  # cast-ok: mcp tools ride along in the guardrail's tool list
                 for form in LiteLLMCompletionResponsesConfig.responses_tools_to_chat_forms(
@@ -463,6 +464,7 @@ class OpenAIResponsesHandler(BaseTranslation):
                 )
                 for tool in form.chat_tools
             ),
+            conversation_supplied=bool(structured_messages),
         )
 
     async def process_input_messages(

tests/test_litellm/llms/openai/chat/guardrail_translation/test_openai_guardrail_handler.py

@@ -2360,6 +2360,19 @@ class TestResponseScanCarriesRequestConversation:
         assert [m["role"] for m in inputs["structured_messages"]] == ["tool", "assistant"]
         assert "tools" not in inputs
 
+    @pytest.mark.asyncio
+    async def test_scan_only_tool_results_without_tool_turns_still_carries_the_reply(self):
+        handler = OpenAIChatCompletionsHandler()
+        guardrail = InputsRecordingGuardrail()
+        guardrail.scan_only_tool_results = True
+        request = {**self._request(), "messages": [{"role": "user", "content": "Delete everything"}]}
+
+        await handler.process_output_response(self._tool_call_response(), guardrail, request_data=request)
+
+        [(_, inputs)] = guardrail.seen
+        assert [m["role"] for m in inputs["structured_messages"]] == ["assistant"]
+        assert inputs["structured_messages"][0]["tool_calls"][0]["function"]["name"] == "run_shell"
+
     @pytest.mark.asyncio
     async def test_response_scan_without_request_data_stays_response_only(self):
         guardrail = InputsRecordingGuardrail()

tests/test_litellm/llms/openai/responses/test_openai_responses_guardrail_handler.py

@@ -3397,3 +3397,15 @@ class TestResponsesResponseScanCarriesRequestConversation:
             "assistant",
         ]
         assert inputs["structured_messages"][-1] == {"role": "assistant", "content": "Paris is the capital"}
+
+    @pytest.mark.asyncio
+    async def test_response_scan_without_request_input_stays_response_only(self):
+        handler = OpenAIResponsesHandler()
+        guardrail = TypedInputsRecordingGuardrail()
+        request = {k: v for k, v in self._request().items() if k not in ("input", "instructions")}
+
+        await handler.process_output_response(self._tool_call_response(), guardrail, request_data=request)
+
+        [(_, inputs)] = guardrail.seen
+        assert "structured_messages" not in inputs
+        assert "tools" not in inputs