From b20225ebafcda17ba0075876d88eefdf740b47e1 Mon Sep 17 00:00:00 2001
From: Yufeng He <40085740+he-yufeng@users.noreply.github.com>
Date: Sat, 30 May 2026 23:22:27 +0800
Subject: [PATCH] fix: drop hosted MCP calls when reasoning is stripped

---
 .../agent_framework_openai/_chat_client.py    |  8 ++++-
 .../tests/openai/test_openai_chat_client.py   | 35 +++++++++++++++++++
 2 files changed, 42 insertions(+), 1 deletion(-)

diff --git a/python/packages/openai/agent_framework_openai/_chat_client.py b/python/packages/openai/agent_framework_openai/_chat_client.py
index 261554fba3..ed5872af21 100644
--- a/python/packages/openai/agent_framework_openai/_chat_client.py
+++ b/python/packages/openai/agent_framework_openai/_chat_client.py
@@ -1492,6 +1492,9 @@ def _prepare_message_for_openai(
         # marker, since the server-stored items would otherwise duplicate the inline ones. Without
         # storage, standalone reasoning items are invalid per the API ("reasoning was provided
         # without its required following item"), so the reasoning branch always drops.
+        drops_reasoning_without_storage = not request_uses_service_side_storage and any(
+            content.type == "text_reasoning" for content in message.contents
+        )
         for content in message.contents:
             match content.type:
                 case "text_reasoning":
@@ -1546,7 +1549,10 @@ def _prepare_message_for_openai(
                     # server-side `id`, so under continuation it would duplicate
                     # the prior response's items (#3295). Drop the call here; the
                     # orphan result is dropped by the coalesce step that follows.
-                    if request_uses_service_side_storage:
+                    #
+                    # Without storage, a reasoning + hosted-MCP pair cannot be replayed
+                    # partially: reasoning is stripped above, and a bare mcp_call is rejected.
+                    if request_uses_service_side_storage or drops_reasoning_without_storage:
                         continue
                     prepared_mcp = self._prepare_content_for_openai(
                         message.role,
diff --git a/python/packages/openai/tests/openai/test_openai_chat_client.py b/python/packages/openai/tests/openai/test_openai_chat_client.py
index e604742e7e..2d036f42bc 100644
--- a/python/packages/openai/tests/openai/test_openai_chat_client.py
+++ b/python/packages/openai/tests/openai/test_openai_chat_client.py
@@ -5648,6 +5648,41 @@ def test_prepare_messages_for_openai_coalesces_mcp_call_and_result_into_single_i
     assert fco_items == [], f"unexpected orphan function_call_output items: {fco_items}"
 
 
+def test_prepare_messages_for_openai_drops_mcp_call_when_paired_reasoning_is_stripped() -> None:
+    client = OpenAIChatClient(model="test-model", api_key="test-key")
+
+    messages = [
+        Message(
+            role="assistant",
+            contents=[
+                Content.from_text_reasoning(id="rs_abc123", text="Need the MCP server."),
+                Content.from_mcp_server_tool_call(
+                    call_id="mcp_abc123",
+                    tool_name="search",
+                    server_name="api_specs",
+                    arguments='{"q": "cats"}',
+                ),
+            ],
+        ),
+        Message(
+            role="tool",
+            contents=[
+                Content.from_mcp_server_tool_result(
+                    call_id="mcp_abc123",
+                    output=[Content.from_text(text="found 10 cats")],
+                )
+            ],
+        ),
+    ]
+
+    result = client._prepare_messages_for_openai(messages, request_uses_service_side_storage=False)
+
+    types = [item.get("type") for item in result if isinstance(item, dict)]
+    assert "reasoning" not in types
+    assert "mcp_call" not in types
+    assert "function_call_output" not in types
+
+
 def test_prepare_messages_for_openai_drops_orphan_mcp_server_tool_result() -> None:
     """When an mcp_server_tool_result has no matching mcp_server_tool_call in
     the message list, it must be dropped, NOT serialized as a