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(