[responsesAPI] prioritize content over summary in reasoning item input (#36516)

Signed-off-by: Andrew Xia <axia@meta.com>
Signed-off-by: Andrew Xia <mitandrewxia@gmail.com>
Signed-off-by: Andrew Xia <axia@fb.com>
Co-authored-by: gemini-code-assist[bot] <176961590+gemini-code-assist[bot]@users.noreply.github.com>
Co-authored-by: Andrew Xia <axia@fb.com>

tests/entrypoints/test_responses_utils.py

 # SPDX-License-Identifier: Apache-2.0
 # SPDX-FileCopyrightText: Copyright contributors to the vLLM project
 
+from unittest.mock import patch
+
 import pytest
 from openai.types.chat import ChatCompletionMessageParam
 from openai.types.responses.response_function_tool_call import ResponseFunctionToolCall
@@ -166,6 +168,184 @@ class TestResponsesUtils:
         assert formatted_item["content"] == "dongyi"
 
 
+class TestReasoningItemContentPriority:
+    """Tests that content is prioritized over summary for reasoning items."""
+
+    def test_content_preferred_over_summary(self):
+        """When both content and summary are present, content should win."""
+        item = ResponseReasoningItem(
+            id="reasoning_1",
+            summary=[
+                Summary(
+                    text="This is a summary",
+                    type="summary_text",
+                )
+            ],
+            type="reasoning",
+            content=[
+                Content(
+                    text="This is the actual content",
+                    type="reasoning_text",
+                )
+            ],
+            encrypted_content=None,
+            status=None,
+        )
+        formatted = _construct_single_message_from_response_item(item)
+        assert formatted["reasoning"] == "This is the actual content"
+
+    def test_content_only(self):
+        """When only content is present (no summary), content is used."""
+        item = ResponseReasoningItem(
+            id="reasoning_2",
+            summary=[],
+            type="reasoning",
+            content=[
+                Content(
+                    text="Content without summary",
+                    type="reasoning_text",
+                )
+            ],
+            encrypted_content=None,
+            status=None,
+        )
+        formatted = _construct_single_message_from_response_item(item)
+        assert formatted["reasoning"] == "Content without summary"
+
+    @patch("vllm.entrypoints.openai.responses.utils.logger")
+    def test_summary_fallback_when_no_content(self, mock_logger):
+        """When content is absent, summary is used as fallback with warning."""
+        item = ResponseReasoningItem(
+            id="reasoning_3",
+            summary=[
+                Summary(
+                    text="Fallback summary text",
+                    type="summary_text",
+                )
+            ],
+            type="reasoning",
+            content=None,
+            encrypted_content=None,
+            status=None,
+        )
+        formatted = _construct_single_message_from_response_item(item)
+        assert formatted["reasoning"] == "Fallback summary text"
+        mock_logger.warning.assert_called_once()
+        assert (
+            "summary text as reasoning content" in mock_logger.warning.call_args[0][0]
+        )
+
+    @patch("vllm.entrypoints.openai.responses.utils.logger")
+    def test_summary_fallback_when_content_empty(self, mock_logger):
+        """When content is an empty list, summary is used as fallback."""
+        item = ResponseReasoningItem(
+            id="reasoning_4",
+            summary=[
+                Summary(
+                    text="Summary when content empty",
+                    type="summary_text",
+                )
+            ],
+            type="reasoning",
+            content=[],
+            encrypted_content=None,
+            status=None,
+        )
+        formatted = _construct_single_message_from_response_item(item)
+        assert formatted["reasoning"] == "Summary when content empty"
+        mock_logger.warning.assert_called_once()
+        assert (
+            "summary text as reasoning content" in mock_logger.warning.call_args[0][0]
+        )
+
+    def test_neither_content_nor_summary(self):
+        """When neither content nor summary is present, reasoning is empty."""
+        item = ResponseReasoningItem(
+            id="reasoning_5",
+            summary=[],
+            type="reasoning",
+            content=None,
+            encrypted_content=None,
+            status=None,
+        )
+        formatted = _construct_single_message_from_response_item(item)
+        assert formatted["reasoning"] == ""
+
+    def test_encrypted_content_raises(self):
+        """Encrypted content should still raise ValueError."""
+        item = ResponseReasoningItem(
+            id="reasoning_6",
+            summary=[
+                Summary(
+                    text="Some summary",
+                    type="summary_text",
+                )
+            ],
+            type="reasoning",
+            content=[
+                Content(
+                    text="Some content",
+                    type="reasoning_text",
+                )
+            ],
+            encrypted_content="ENCRYPTED",
+            status=None,
+        )
+        with pytest.raises(ValueError):
+            _construct_single_message_from_response_item(item)
+
+    @patch("vllm.entrypoints.openai.responses.utils.logger")
+    def test_summary_with_multiple_entries_uses_first(self, mock_logger):
+        """When multiple summary entries exist, the first one is used."""
+        item = ResponseReasoningItem(
+            id="reasoning_7",
+            summary=[
+                Summary(
+                    text="First summary",
+                    type="summary_text",
+                ),
+                Summary(
+                    text="Second summary",
+                    type="summary_text",
+                ),
+            ],
+            type="reasoning",
+            content=None,
+            encrypted_content=None,
+            status=None,
+        )
+        formatted = _construct_single_message_from_response_item(item)
+        assert formatted["reasoning"] == "First summary"
+        mock_logger.warning.assert_called_once()
+        assert (
+            "summary text as reasoning content" in mock_logger.warning.call_args[0][0]
+        )
+
+    @patch("vllm.entrypoints.openai.responses.utils.logger")
+    def test_no_warning_when_content_used(self, mock_logger):
+        """No warning should be emitted when content is available."""
+        item = ResponseReasoningItem(
+            id="reasoning_8",
+            summary=[
+                Summary(
+                    text="Summary text",
+                    type="summary_text",
+                )
+            ],
+            type="reasoning",
+            content=[
+                Content(
+                    text="Content text",
+                    type="reasoning_text",
+                )
+            ],
+            encrypted_content=None,
+            status=None,
+        )
+        _construct_single_message_from_response_item(item)
+        mock_logger.warning.assert_not_called()
+
+
 class TestShouldContinueFinalMessage:
     """Tests for should_continue_final_message function.
 

vllm/entrypoints/openai/responses/utils.py

@@ -24,6 +24,9 @@ from vllm import envs
 from vllm.entrypoints.constants import MCP_PREFIX
 from vllm.entrypoints.openai.chat_completion.protocol import ChatCompletionMessageParam
 from vllm.entrypoints.openai.responses.protocol import ResponseInputOutputItem
+from vllm.logger import init_logger
+
+logger = init_logger(__name__)
 
 
 def should_continue_final_message(
@@ -191,10 +194,16 @@ def _construct_single_message_from_response_item(
         reasoning_content = ""
         if item.encrypted_content:
             raise ValueError("Encrypted content is not supported.")
-        if len(item.summary) == 1:
-            reasoning_content = item.summary[0].text
-        elif item.content and len(item.content) == 1:
+        elif item.content and len(item.content) >= 1:
             reasoning_content = item.content[0].text
+        elif len(item.summary) >= 1:
+            reasoning_content = item.summary[0].text
+            logger.warning(
+                "Using summary text as reasoning content for item %s. "
+                "Please use content instead of summary for "
+                "reasoning items.",
+                item.id,
+            )
         return {
             "role": "assistant",
             "reasoning": reasoning_content,