fix(responses): keep cache breakpoints out of non-bridge converter callers

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

litellm/completion_extras/litellm_responses_transformation/transformation.py

@@ -393,6 +393,20 @@ class LiteLLMResponsesTransformationHandler(CompletionTransformationBridge):
         return None, index
 
     def convert_chat_completion_messages_to_responses_api(
+        self,
+        messages: list["AllMessageValues"],
+        *,
+        keep_prompt_cache_breakpoints: bool = False,
+    ) -> tuple[list[object], str | None]:
+        converted_input_items, instructions = self._convert_chat_completion_messages_to_responses_input(messages)
+        return (
+            converted_input_items
+            if keep_prompt_cache_breakpoints
+            else _strip_prompt_cache_breakpoints(converted_input_items),
+            instructions,
+        )
+
+    def _convert_chat_completion_messages_to_responses_input(
         self, messages: list["AllMessageValues"]
     ) -> tuple[list[object], str | None]:
         input_items: Final[list[object]] = []
@@ -623,23 +637,19 @@ class LiteLLMResponsesTransformationHandler(CompletionTransformationBridge):
         litellm_logging_obj: "LiteLLMLoggingObj",
         client: object | None = None,
     ) -> dict:
-        converted_input_items, converted_instructions = self.convert_chat_completion_messages_to_responses_api(messages)
         base_model: Final = litellm_params.get("base_model")
         supports_prompt_cache_breakpoint: Final = supports_openai_prompt_cache_breakpoint(model) or (
             isinstance(base_model, str) and bool(base_model) and supports_openai_prompt_cache_breakpoint(base_model)
         )
-        input_items_without_unsupported_markers: Final = (
-            converted_input_items
-            if supports_prompt_cache_breakpoint
-            else _strip_prompt_cache_breakpoints(converted_input_items)
+        converted_input_items, converted_instructions = self.convert_chat_completion_messages_to_responses_api(
+            messages,
+            keep_prompt_cache_breakpoints=supports_prompt_cache_breakpoint,
         )
         # OpenAI's Responses API rejects an empty input. For a system-only
         # request, carry the system message as a system-role input item instead
         # of instructions, mirroring how non-string system content is already
         # handled in convert_chat_completion_messages_to_responses_api.
-        is_system_only_request: Final = (
-            not input_items_without_unsupported_markers and converted_instructions is not None
-        )
+        is_system_only_request: Final = not converted_input_items and converted_instructions is not None
         input_items: Final = (
             [
                 {
@@ -649,7 +659,7 @@ class LiteLLMResponsesTransformationHandler(CompletionTransformationBridge):
                 }
             ]
             if is_system_only_request
-            else input_items_without_unsupported_markers
+            else converted_input_items
         )
         instructions: Final = None if is_system_only_request else converted_instructions
 

tests/unit/completion_extras/litellm_responses_transformation/test_completion_extras_litellm_responses_transformation_transformation.py

@@ -1,3 +1,4 @@
+import copy
 import datetime
 import json
 import os
@@ -4333,6 +4334,120 @@ def test_prompt_cache_breakpoints_are_dropped_from_function_call_output_for_unsu
     ]
 
 
+def test_convert_chat_completion_messages_to_responses_api_drops_prompt_cache_breakpoints_unless_kept() -> None:
+    handler: Final = LiteLLMResponsesTransformationHandler()
+    cache_breakpoint: Final = {"mode": "explicit"}
+    image_data_url: Final = "data:image/png;base64,iVBORw0KGgoAAAANSUhEUgAAAAEAAAABCAYAAAAfFcSJAAAADUlEQVR42mP8z8DwHwAFBQIAX8jx0gAAAABJRU5ErkJggg=="
+    file_data: Final = "data:application/pdf;base64,JVBERi0xLjQK"
+    messages: Final = cast(
+        list[AllMessageValues],
+        [
+            {
+                "role": "user",
+                "content": [
+                    {"type": "text", "text": "Review these inputs", "prompt_cache_breakpoint": cache_breakpoint},
+                    {
+                        "type": "image_url",
+                        "image_url": {"url": image_data_url},
+                        "prompt_cache_breakpoint": cache_breakpoint,
+                    },
+                    {
+                        "type": "file",
+                        "file": {"file_data": file_data, "filename": "input.pdf"},
+                        "prompt_cache_breakpoint": cache_breakpoint,
+                    },
+                ],
+            },
+            {
+                "role": "assistant",
+                "tool_calls": [
+                    {
+                        "id": "call_1",
+                        "type": "function",
+                        "function": {"name": "lookup", "arguments": "{}"},
+                    }
+                ],
+            },
+            {
+                "role": "tool",
+                "tool_call_id": "call_1",
+                "content": [
+                    {"type": "text", "text": "Tool result", "prompt_cache_breakpoint": cache_breakpoint}
+                ],
+            },
+        ],
+    )
+    messages_before: Final = copy.deepcopy(messages)
+
+    default_input, default_instructions = handler.convert_chat_completion_messages_to_responses_api(messages)
+    kept_input, kept_instructions = handler.convert_chat_completion_messages_to_responses_api(
+        messages,
+        keep_prompt_cache_breakpoints=True,
+    )
+
+    assert default_instructions is None
+    assert default_input == [
+        {
+            "type": "message",
+            "role": "user",
+            "content": [
+                {"type": "input_text", "text": "Review these inputs"},
+                {"type": "input_image", "image_url": image_data_url, "detail": "auto"},
+                {"type": "input_file", "file_data": file_data, "filename": "input.pdf"},
+            ],
+        },
+        {
+            "type": "function_call",
+            "call_id": "call_1",
+            "name": "lookup",
+            "arguments": "{}",
+        },
+        {
+            "type": "function_call_output",
+            "call_id": "call_1",
+            "output": [{"type": "input_text", "text": "Tool result"}],
+        },
+    ]
+    assert kept_instructions is None
+    assert kept_input == [
+        {
+            "type": "message",
+            "role": "user",
+            "content": [
+                {
+                    "type": "input_text",
+                    "text": "Review these inputs",
+                    "prompt_cache_breakpoint": cache_breakpoint,
+                },
+                {
+                    "type": "input_image",
+                    "image_url": image_data_url,
+                    "detail": "auto",
+                    "prompt_cache_breakpoint": cache_breakpoint,
+                },
+                {
+                    "type": "input_file",
+                    "file_data": file_data,
+                    "filename": "input.pdf",
+                    "prompt_cache_breakpoint": cache_breakpoint,
+                },
+            ],
+        },
+        {
+            "type": "function_call",
+            "call_id": "call_1",
+            "name": "lookup",
+            "arguments": "{}",
+        },
+        {
+            "type": "function_call_output",
+            "call_id": "call_1",
+            "output": [{"type": "input_text", "text": "Tool result", "prompt_cache_breakpoint": cache_breakpoint}],
+        },
+    ]
+    assert messages == messages_before
+
+
 @pytest.mark.parametrize(
     ("litellm_params", "keep_marker"),
     (({"base_model": "gpt-5.6"}, True), ({}, False)),