From 2ae5e6f1a4d978c914b06f167de8fcf0d0952a28 Mon Sep 17 00:00:00 2001
From: Devin AI <158243242+devin-ai-integration[bot]@users.noreply.github.com>
Date: Sun, 12 Jul 2026 07:15:27 +0000
Subject: [PATCH] fix(responses): preserve tool output adjacency

---
 .../transformation.py                         | 19 +++++++++
 .../test_litellm_completion_responses.py      | 41 +++++++++++++++++++
 2 files changed, 60 insertions(+)

diff --git a/litellm/responses/litellm_completion_transformation/transformation.py b/litellm/responses/litellm_completion_transformation/transformation.py
index 6b1ca3564e3..7e75696890c 100644
--- a/litellm/responses/litellm_completion_transformation/transformation.py
+++ b/litellm/responses/litellm_completion_transformation/transformation.py
@@ -402,6 +402,25 @@ class LiteLLMCompletionResponsesConfig:
                     )
                 )
 
+                if (
+                    messages
+                    and len(chat_completion_messages) == 1
+                    and not LiteLLMCompletionResponsesConfig._is_input_item_function_call(input_item=_input)
+                    and not LiteLLMCompletionResponsesConfig._is_input_item_tool_call_output(input_item=_input)
+                ):
+                    last_msg = messages[-1]
+                    new_msg = chat_completion_messages[0]
+                    if (
+                        isinstance(last_msg, dict)
+                        and isinstance(new_msg, dict)
+                        and last_msg.get("role") == "assistant"
+                        and last_msg.get("tool_calls")
+                        and last_msg.get("content") is None
+                        and new_msg.get("role") == "assistant"
+                    ):
+                        last_msg["content"] = new_msg.get("content")
+                        continue
+
                 if LiteLLMCompletionResponsesConfig._is_input_item_function_call(input_item=_input):
                     call_id_raw = _input.get("call_id") or _input.get("id") or ""
                     if call_id_raw:
diff --git a/tests/test_litellm/responses/litellm_completion_transformation/test_litellm_completion_responses.py b/tests/test_litellm/responses/litellm_completion_transformation/test_litellm_completion_responses.py
index d8e3f495ced..626f3d9b5da 100644
--- a/tests/test_litellm/responses/litellm_completion_transformation/test_litellm_completion_responses.py
+++ b/tests/test_litellm/responses/litellm_completion_transformation/test_litellm_completion_responses.py
@@ -2370,6 +2370,47 @@ class TestStreamingIDConsistency:
             len(tool_messages) == 2
         ), f"Expected 2 tool messages, got {len(tool_messages)}"
 
+    def test_assistant_message_between_function_call_and_output_is_merged(self):
+        input_items = [
+            {"type": "message", "role": "user", "content": "Run pwd"},
+            {
+                "type": "function_call",
+                "call_id": "call_01",
+                "name": "exec_command",
+                "arguments": '{"cmd":"pwd"}',
+            },
+            {
+                "type": "message",
+                "role": "assistant",
+                "content": [
+                    {
+                        "type": "output_text",
+                        "text": "I'll inspect the working directory.",
+                    }
+                ],
+            },
+            {
+                "type": "function_call_output",
+                "call_id": "call_01",
+                "output": "/workspace",
+            },
+        ]
+
+        messages = LiteLLMCompletionResponsesConfig._transform_response_input_param_to_chat_completion_message(
+            input=input_items
+        )
+
+        assert [message.get("role") for message in messages] == [
+            "user",
+            "assistant",
+            "tool",
+        ]
+        assert messages[1].get("content") == [
+            {"type": "text", "text": "I'll inspect the working directory."}
+        ]
+        assert messages[1].get("tool_calls")[0].get("id") == "call_01"
+        assert messages[2].get("tool_call_id") == "call_01"
+
     def test_single_tool_call_still_works_after_merge_fix(self):
         """
         Ensure the parallel-tool-call merging fix does not break the existing