Python: Fix duplicate tool result messages in handoff workflow

python/packages/core/agent_framework/_workflows/_handoff.py

@@ -281,6 +281,28 @@ def _target_from_tool_name(name: str | None) -> str | None:
     return None
 
 
+def _has_tool_result_for_call(conversation: list[ChatMessage], call_id: str) -> bool:
+    """Check if a tool result message exists for the given call_id.
+
+    Args:
+        conversation: The conversation history to check
+        call_id: The function call ID to look for
+
+    Returns:
+        True if a tool result with matching call_id exists, False otherwise
+    """
+    for msg in conversation:
+        if msg.role != Role.TOOL:
+            continue
+
+        for content in msg.contents:
+            if isinstance(content, FunctionResultContent):
+                if content.call_id == call_id:
+                    return True
+
+    return False
+
+
 class _HandoffCoordinator(BaseGroupChatOrchestrator):
     """Coordinates agent-to-agent transfers and user turn requests."""
 
@@ -482,6 +504,14 @@ def _append_tool_acknowledgement(
         if not call_id:
             return
 
+        # Skip if tool result already exists to avoid duplicates from _AutoHandoffMiddleware
+        if _has_tool_result_for_call(conversation, call_id):
+            logger.debug(
+                f"Tool result for call_id '{call_id}' already exists, "
+                f"skipping duplicate for handoff to '{resolved_id}'"
+            )
+            return
+
         result_payload: Any = {"handoff_to": resolved_id}
         result_content = FunctionResultContent(call_id=call_id, result=result_payload)
         tool_message = ChatMessage(

python/packages/core/tests/workflow/test_handoff.py

@@ -727,3 +727,101 @@ async def test_return_to_previous_state_serialization():
 
     # Verify current_agent_id was restored
     assert coordinator2._current_agent_id == "specialist_a", "Current agent should be restored from checkpoint"  # type: ignore[reportPrivateUsage]
+
+
+def test_duplicate_tool_result_detection(caplog):
+    """Test that _append_tool_acknowledgement skips duplicates and logs debug message."""
+    from agent_framework import FunctionResultContent
+    from agent_framework._workflows._handoff import (  # type: ignore[reportPrivateUsage]
+        _HandoffCoordinator,
+        _has_tool_result_for_call,
+    )
+
+    # Test _has_tool_result_for_call helper function
+    call_id_1 = "call-123"
+    call_id_2 = "call-456"
+
+    # Create a conversation with an existing tool result
+    existing_tool_result = FunctionResultContent(call_id=call_id_1, result={"handoff_to": "specialist_a"})
+    existing_tool_msg = ChatMessage(role=Role.TOOL, contents=[existing_tool_result], author_name="handoff_tool")
+
+    conversation_with_result = [
+        ChatMessage(role=Role.USER, text="Help me"),
+        ChatMessage(role=Role.ASSISTANT, text="Routing to specialist"),
+        existing_tool_msg,
+    ]
+
+    # Should find the existing tool result
+    assert _has_tool_result_for_call(conversation_with_result, call_id_1) is True, (
+        "Should detect existing tool result"
+    )
+
+    # Should not find a tool result with different call_id
+    assert _has_tool_result_for_call(conversation_with_result, call_id_2) is False, (
+        "Should not find tool result with different call_id"
+    )
+
+    # Test on conversation without tool results
+    conversation_without_result = [
+        ChatMessage(role=Role.USER, text="Help me"),
+        ChatMessage(role=Role.ASSISTANT, text="Routing to specialist"),
+    ]
+    assert _has_tool_result_for_call(conversation_without_result, call_id_1) is False, (
+        "Should not find tool result in conversation without tool messages"
+    )
+
+    # Test _append_tool_acknowledgement skips duplicates
+    coordinator = _HandoffCoordinator(
+        starting_agent_id="triage",
+        specialist_ids={"specialist_a": "specialist_a"},
+        input_gateway_id="gateway",
+        termination_condition=lambda conv: False,
+        id="test-coordinator",
+    )
+
+    # Create a function call for handoff
+    handoff_call = FunctionCallContent(call_id=call_id_1, name="handoff_to_specialist_a", arguments="{}")
+
+    # Conversation already has a tool result for this call_id (simulating _AutoHandoffMiddleware behavior)
+    conversation_with_duplicate = list(conversation_with_result)
+
+    # Try to append tool acknowledgement - should skip due to duplicate
+    # Set caplog to capture DEBUG level logs from the handoff module
+    import logging
+
+    caplog.set_level(logging.DEBUG, logger="agent_framework._workflows._handoff")
+    coordinator._append_tool_acknowledgement(  # type: ignore[reportPrivateUsage]
+        conversation_with_duplicate, handoff_call, "specialist_a"
+    )
+
+    # Verify conversation wasn't modified (no duplicate added)
+    assert len(conversation_with_duplicate) == 3, "Conversation should not have duplicate tool result added"
+
+    # Verify debug log was emitted
+    assert any(
+        "Tool result for call_id 'call-123' already exists" in record.message for record in caplog.records
+    ), "Should log debug message when skipping duplicate"
+
+    assert any(
+        "skipping duplicate for handoff to 'specialist_a'" in record.message for record in caplog.records
+    ), "Debug message should mention the target specialist"
+
+    # Test that tool acknowledgement IS added when no duplicate exists
+    conversation_no_duplicate = [
+        ChatMessage(role=Role.USER, text="Help me"),
+        ChatMessage(role=Role.ASSISTANT, text="Routing to specialist"),
+    ]
+    new_call = FunctionCallContent(call_id="call-new", name="handoff_to_specialist_a", arguments="{}")
+
+    caplog.clear()
+    coordinator._append_tool_acknowledgement(conversation_no_duplicate, new_call, "specialist_a")  # type: ignore[reportPrivateUsage]
+
+    # Should have added the tool result
+    assert len(conversation_no_duplicate) == 3, "Tool result should be added when no duplicate exists"
+    last_msg = conversation_no_duplicate[-1]
+    assert last_msg.role == Role.TOOL, "Last message should be a tool result"
+
+    # Should NOT log the debug message (no duplicate detected)
+    assert not any(
+        "already exists" in record.message for record in caplog.records
+    ), "Should not log duplicate message when adding new tool result"