fix(moderations): stop the router image check from 500ing on a list input (#49454)

* fix(moderations): stop the router image check from 500ing on a list input

* fix(moderations): give the list cast its cast-ok reason

* fix(moderations): type the responses input guard and keep SDK compaction items

* fix(moderations): import the compaction item through litellm.types and mark the TypeIs import

* fix(moderations): sort the compaction item import

---------

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

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

@@ -40,7 +40,11 @@ from typing import TYPE_CHECKING, Any, Final, NamedTuple, Protocol, TypeVar, Uni
 
 from openai.types.responses.response_output_refusal import ResponseOutputRefusal
 from pydantic import BaseModel, ConfigDict, TypeAdapter, ValidationError
-from typing_extensions import ReadOnly, TypedDict
+from typing_extensions import (
+    ReadOnly,
+    TypedDict,
+    TypeIs,  # noqa: TID251  # TypeIs reaches typing only on 3.13
+)
 
 from litellm._logging import verbose_proxy_logger
 from litellm.completion_extras.litellm_responses_transformation.transformation import (
@@ -100,6 +104,7 @@ from litellm.types.llms.openai import (
     OutputTextDeltaEvent,
     OutputTextDoneEvent,
     ResponseAPIUsage,
+    ResponseCompactionItem,
     ResponseCompletedEvent,
     ResponsesAPIOptionalRequestParams,
     ResponsesAPIResponse,
@@ -712,6 +717,15 @@ def _next_stream_sequence_number(responses_so_far: Sequence[object] | None) -> i
     return next((n + 1 for n in sequence_numbers if isinstance(n, int)), 0)
 
 
+def _is_responses_input(
+    input_data: object,
+) -> TypeIs["str | ResponseInputParam"]:  # guard-ok: str, or a list of Mapping items
+    if isinstance(input_data, str):
+        return True
+    items: Final = cast(list[object], input_data)  # cast-ok: isinstance narrows to list[Unknown] only
+    return isinstance(input_data, list) and all(isinstance(item, (Mapping, ResponseCompactionItem)) for item in items)
+
+
 class OpenAIResponsesHandler(BaseTranslation):
     """
     Handler for processing OpenAI Responses API with guardrails.
@@ -733,8 +747,8 @@ class OpenAIResponsesHandler(BaseTranslation):
         Transforms `input` (string or ResponseInputParam) and optional
         `instructions` into chat completion messages.
         """
-        input_data: Final = data.get("input")
-        if input_data is None:
+        input_data: Final[object] = data.get("input")
+        if not _is_responses_input(input_data):
             return None
         messages: Final = LiteLLMCompletionResponsesConfig.transform_responses_api_input_to_messages(
             input=input_data,

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

@@ -29,6 +29,7 @@ from openai.types.responses import (
     ResponseOutputRefusal,
     ResponseOutputText,
 )
+from openai.types.responses.response_compaction_item import ResponseCompactionItem
 
 from litellm.integrations.custom_guardrail import CustomGuardrail
 from litellm.litellm_core_utils.litellm_logging import Logging as LiteLLMLoggingObj
@@ -3349,6 +3350,25 @@ class TestGetStructuredMessages:
         result = handler.get_structured_messages(data)
         assert result is None
 
+    def test_should_return_none_for_a_moderation_style_list_of_strings(self):
+        handler = OpenAIResponsesHandler()
+        data = {"model": "omni-moderation-latest", "input": ["safe text", "more safe text"]}
+        assert handler.get_structured_messages(data) is None
+
+    def test_should_keep_an_image_item_replayed_with_an_sdk_compaction_item(self):
+        handler = OpenAIResponsesHandler()
+        image_url = "https://example.com/cat.png"
+        data = {
+            "model": "gpt-5.5",
+            "input": [
+                ResponseCompactionItem(type="compaction", id="cmp_1", encrypted_content="abc"),
+                {"role": "user", "content": [{"type": "input_image", "image_url": image_url}]},
+            ],
+        }
+        result = handler.get_structured_messages(data)
+        assert result is not None
+        assert image_url in json.dumps(result)
+
 
 class ToolAppendingGuardrail(CustomGuardrail):
     """Guardrail that appends a new function tool, mimicking a guardrail that

tests/unit/test_router/test_router.py

@@ -31445,6 +31445,7 @@ def test_request_carries_image_sees_chat_parts_and_responses_input_items():
     assert litellm.Router._request_carries_image(None, {"input": _IMAGE_RESPONSES_INPUT}) is True
     assert litellm.Router._request_carries_image([{"role": "user", "content": "Say hi"}], {}) is False
     assert litellm.Router._request_carries_image(None, {"input": "Say hi"}) is False
+    assert litellm.Router._request_carries_image(None, {"input": ["safe text", "more safe text"]}) is False
 
 
 @pytest.mark.asyncio