diff --git a/python/packages/core/agent_framework/_workflows/_handoff.py b/python/packages/core/agent_framework/_workflows/_handoff.py
index 8e0a7aec1e..49de54f5d2 100644
--- a/python/packages/core/agent_framework/_workflows/_handoff.py
+++ b/python/packages/core/agent_framework/_workflows/_handoff.py
@@ -130,19 +130,57 @@ def _clone_chat_agent(agent: ChatAgent) -> ChatAgent:
 
 @dataclass
 class HandoffUserInputRequest:
-    """Request message emitted when the workflow needs fresh user input."""
+    """Request message emitted when the workflow needs fresh user input.
+
+    Note: The conversation field is intentionally excluded from checkpoint serialization
+    to prevent duplication. The conversation is preserved in the coordinator's state
+    and will be reconstructed on restore. See issue #2667.
+    """
 
     conversation: list[ChatMessage]
     awaiting_agent_id: str
     prompt: str
     source_executor_id: str
 
+    def to_dict(self) -> dict[str, Any]:
+        """Serialize to dict, excluding conversation to prevent checkpoint duplication.
+
+        The conversation is already preserved in the workflow coordinator's state.
+        Including it here would cause duplicate messages when restoring from checkpoint.
+        """
+        return {
+            "awaiting_agent_id": self.awaiting_agent_id,
+            "prompt": self.prompt,
+            "source_executor_id": self.source_executor_id,
+        }
+
+    @classmethod
+    def from_dict(cls, data: dict[str, Any]) -> "HandoffUserInputRequest":
+        """Deserialize from dict, initializing conversation as empty.
+
+        The conversation will be reconstructed from the coordinator's state on restore.
+        """
+        return cls(
+            conversation=[],
+            awaiting_agent_id=data["awaiting_agent_id"],
+            prompt=data["prompt"],
+            source_executor_id=data["source_executor_id"],
+        )
+
 
 @dataclass
 class _ConversationWithUserInput:
-    """Internal message carrying full conversation + new user messages from gateway to coordinator."""
+    """Internal message carrying full conversation + new user messages from gateway to coordinator.
+
+    Attributes:
+        full_conversation: The conversation messages to process.
+        is_post_restore: If True, indicates this message was created after a checkpoint restore.
+            The coordinator should append these messages to its existing conversation rather
+            than replacing it. This prevents duplicate messages (see issue #2667).
+    """
 
     full_conversation: list[ChatMessage] = field(default_factory=lambda: [])  # type: ignore[misc]
+    is_post_restore: bool = False
 
 
 @dataclass
@@ -439,9 +477,25 @@ async def handle_user_input(
         message: _ConversationWithUserInput,
         ctx: WorkflowContext[AgentExecutorRequest, list[ChatMessage]],
     ) -> None:
-        """Receive full conversation with new user input from gateway, update history, trim for agent."""
-        # Update authoritative conversation
-        self._conversation = list(message.full_conversation)
+        """Receive user input from gateway, update history, and route to agent.
+
+        The message.full_conversation may contain:
+        - Full conversation history + new user messages (normal flow)
+        - Only new user messages (post-checkpoint-restore flow, see issue #2667)
+
+        The gateway sets message.is_post_restore=True when resuming after a checkpoint
+        restore. In that case, we append the new messages to the existing conversation
+        rather than replacing it.
+        """
+        incoming = message.full_conversation
+
+        if message.is_post_restore and self._conversation:
+            # Post-restore: append new user messages to existing conversation
+            # The coordinator already has its conversation restored from checkpoint
+            self._conversation.extend(incoming)
+        else:
+            # Normal flow: replace with full conversation
+            self._conversation = list(incoming) if incoming else self._conversation
 
         # Reset autonomous turn counter on new user input
         self._autonomous_turns = 0
@@ -626,15 +680,24 @@ async def resume_from_user(
         response: object,
         ctx: WorkflowContext[_ConversationWithUserInput],
     ) -> None:
-        """Convert user input responses back into chat messages and resume the workflow."""
-        # Reconstruct full conversation with new user input
-        conversation = list(original_request.conversation)
+        """Convert user input responses back into chat messages and resume the workflow.
+
+        After checkpoint restore, original_request.conversation will be empty (not serialized
+        to prevent duplication - see issue #2667). In this case, we send only the new user
+        messages and let the coordinator append them to its already-restored conversation.
+        """
         user_messages = _as_user_messages(response)
-        conversation.extend(user_messages)
 
-        # Send full conversation back to coordinator (not trimmed)
-        # Coordinator will update its authoritative history and trim for agent
-        message = _ConversationWithUserInput(full_conversation=conversation)
+        if original_request.conversation:
+            # Normal flow: have conversation history from the original request
+            conversation = list(original_request.conversation)
+            conversation.extend(user_messages)
+            message = _ConversationWithUserInput(full_conversation=conversation, is_post_restore=False)
+        else:
+            # Post-restore flow: conversation was not serialized, send only new user messages
+            # The coordinator will append these to its already-restored conversation
+            message = _ConversationWithUserInput(full_conversation=user_messages, is_post_restore=True)
+
         await ctx.send_message(message, target_id="handoff-coordinator")
 
 
diff --git a/python/packages/core/tests/workflow/test_handoff.py b/python/packages/core/tests/workflow/test_handoff.py
index 0ceccfaf15..077cb7321e 100644
--- a/python/packages/core/tests/workflow/test_handoff.py
+++ b/python/packages/core/tests/workflow/test_handoff.py
@@ -25,7 +25,12 @@
 from agent_framework._mcp import MCPTool
 from agent_framework._workflows import AgentRunEvent
 from agent_framework._workflows import _handoff as handoff_module  # type: ignore
-from agent_framework._workflows._handoff import _clone_chat_agent  # type: ignore[reportPrivateUsage]
+from agent_framework._workflows._checkpoint_encoding import decode_checkpoint_value, encode_checkpoint_value
+from agent_framework._workflows._handoff import (
+    _clone_chat_agent,  # type: ignore[reportPrivateUsage]
+    _ConversationWithUserInput,
+    _UserInputGateway,
+)
 from agent_framework._workflows._workflow_builder import WorkflowBuilder
 
 
@@ -775,3 +780,402 @@ 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]
+
+
+async def test_handoff_user_input_request_checkpoint_excludes_conversation():
+    """Test that HandoffUserInputRequest serialization excludes conversation to prevent duplication.
+
+    Issue #2667: When checkpointing a workflow with a pending HandoffUserInputRequest,
+    the conversation field gets serialized twice: once in the RequestInfoEvent's data
+    and once in the coordinator's conversation state. On restore, this causes duplicate
+    messages.
+
+    The fix is to exclude the conversation field during checkpoint serialization since
+    the conversation is already preserved in the coordinator's state.
+    """
+    # Create a conversation history
+    conversation = [
+        ChatMessage(role=Role.USER, text="Hello"),
+        ChatMessage(role=Role.ASSISTANT, text="Hi there!"),
+        ChatMessage(role=Role.USER, text="Help me"),
+    ]
+
+    # Create a HandoffUserInputRequest with the conversation
+    request = HandoffUserInputRequest(
+        conversation=conversation,
+        awaiting_agent_id="specialist_agent",
+        prompt="Please provide your input",
+        source_executor_id="gateway",
+    )
+
+    # Encode the request (simulating checkpoint save)
+    encoded = encode_checkpoint_value(request)
+
+    # Verify conversation is NOT in the encoded output
+    # The fix should exclude conversation from serialization
+    assert isinstance(encoded, dict)
+
+    # If using MODEL_MARKER strategy (to_dict/from_dict)
+    if "__af_model__" in encoded or "__af_dataclass__" in encoded:
+        value = encoded.get("value", {})
+        assert "conversation" not in value, "conversation should be excluded from checkpoint serialization"
+
+    # Decode the request (simulating checkpoint restore)
+    decoded = decode_checkpoint_value(encoded)
+
+    # Verify the decoded request is a HandoffUserInputRequest
+    assert isinstance(decoded, HandoffUserInputRequest)
+
+    # Verify other fields are preserved
+    assert decoded.awaiting_agent_id == "specialist_agent"
+    assert decoded.prompt == "Please provide your input"
+    assert decoded.source_executor_id == "gateway"
+
+    # Conversation should be an empty list after deserialization
+    # (will be reconstructed from coordinator state on restore)
+    assert decoded.conversation == []
+
+
+async def test_handoff_user_input_request_roundtrip_preserves_metadata():
+    """Test that non-conversation fields survive checkpoint roundtrip."""
+    request = HandoffUserInputRequest(
+        conversation=[ChatMessage(role=Role.USER, text="test")],
+        awaiting_agent_id="test_agent",
+        prompt="Enter your response",
+        source_executor_id="test_gateway",
+    )
+
+    # Roundtrip through checkpoint encoding
+    encoded = encode_checkpoint_value(request)
+    decoded = decode_checkpoint_value(encoded)
+
+    assert isinstance(decoded, HandoffUserInputRequest)
+    assert decoded.awaiting_agent_id == request.awaiting_agent_id
+    assert decoded.prompt == request.prompt
+    assert decoded.source_executor_id == request.source_executor_id
+
+
+async def test_request_info_event_with_handoff_user_input_request():
+    """Test RequestInfoEvent serialization with HandoffUserInputRequest data."""
+    conversation = [
+        ChatMessage(role=Role.USER, text="Hello"),
+        ChatMessage(role=Role.ASSISTANT, text="How can I help?"),
+    ]
+
+    request = HandoffUserInputRequest(
+        conversation=conversation,
+        awaiting_agent_id="specialist",
+        prompt="Provide input",
+        source_executor_id="gateway",
+    )
+
+    # Create a RequestInfoEvent wrapping the request
+    event = RequestInfoEvent(
+        request_id="test-request-123",
+        source_executor_id="gateway",
+        request_data=request,
+        response_type=object,
+    )
+
+    # Serialize the event
+    event_dict = event.to_dict()
+
+    # Verify the data field doesn't contain conversation
+    data_encoded = event_dict["data"]
+    if isinstance(data_encoded, dict) and ("__af_model__" in data_encoded or "__af_dataclass__" in data_encoded):
+        value = data_encoded.get("value", {})
+        assert "conversation" not in value
+
+    # Deserialize and verify
+    restored_event = RequestInfoEvent.from_dict(event_dict)
+    assert isinstance(restored_event.data, HandoffUserInputRequest)
+    assert restored_event.data.awaiting_agent_id == "specialist"
+    assert restored_event.data.conversation == []
+
+
+async def test_handoff_user_input_request_to_dict_excludes_conversation():
+    """Test that to_dict() method excludes conversation field."""
+    conversation = [
+        ChatMessage(role=Role.USER, text="Hello"),
+        ChatMessage(role=Role.ASSISTANT, text="Hi!"),
+    ]
+
+    request = HandoffUserInputRequest(
+        conversation=conversation,
+        awaiting_agent_id="agent1",
+        prompt="Enter input",
+        source_executor_id="gateway",
+    )
+
+    # Call to_dict directly
+    data = request.to_dict()
+
+    # Verify conversation is excluded
+    assert "conversation" not in data
+    assert data["awaiting_agent_id"] == "agent1"
+    assert data["prompt"] == "Enter input"
+    assert data["source_executor_id"] == "gateway"
+
+
+async def test_handoff_user_input_request_from_dict_creates_empty_conversation():
+    """Test that from_dict() creates an instance with empty conversation."""
+    data = {
+        "awaiting_agent_id": "agent1",
+        "prompt": "Enter input",
+        "source_executor_id": "gateway",
+    }
+
+    request = HandoffUserInputRequest.from_dict(data)
+
+    assert request.conversation == []
+    assert request.awaiting_agent_id == "agent1"
+    assert request.prompt == "Enter input"
+    assert request.source_executor_id == "gateway"
+
+
+async def test_user_input_gateway_resume_handles_empty_conversation():
+    """Test that _UserInputGateway.resume_from_user handles post-restore scenario.
+
+    After checkpoint restore, the HandoffUserInputRequest will have an empty
+    conversation. The gateway should handle this by sending only the new user
+    messages to the coordinator.
+    """
+    from unittest.mock import AsyncMock
+
+    # Create a gateway
+    gateway = _UserInputGateway(
+        starting_agent_id="coordinator",
+        prompt="Enter input",
+        id="test-gateway",
+    )
+
+    # Simulate post-restore: request with empty conversation
+    restored_request = HandoffUserInputRequest(
+        conversation=[],  # Empty after restore
+        awaiting_agent_id="specialist",
+        prompt="Enter input",
+        source_executor_id="test-gateway",
+    )
+
+    # Create mock context
+    mock_ctx = MagicMock()
+    mock_ctx.send_message = AsyncMock()
+
+    # Call resume_from_user with a user response
+    await gateway.resume_from_user(restored_request, "New user message", mock_ctx)
+
+    # Verify send_message was called
+    mock_ctx.send_message.assert_called_once()
+
+    # Get the message that was sent
+    call_args = mock_ctx.send_message.call_args
+    sent_message = call_args[0][0]
+
+    # Verify it's a _ConversationWithUserInput
+    assert isinstance(sent_message, _ConversationWithUserInput)
+
+    # Verify it contains only the new user message (not any history)
+    assert len(sent_message.full_conversation) == 1
+    assert sent_message.full_conversation[0].role == Role.USER
+    assert sent_message.full_conversation[0].text == "New user message"
+
+
+async def test_user_input_gateway_resume_with_full_conversation():
+    """Test that _UserInputGateway.resume_from_user handles normal flow correctly.
+
+    In normal flow (no checkpoint restore), the HandoffUserInputRequest has
+    the full conversation. The gateway should send the full conversation
+    plus the new user messages.
+    """
+    from unittest.mock import AsyncMock
+
+    # Create a gateway
+    gateway = _UserInputGateway(
+        starting_agent_id="coordinator",
+        prompt="Enter input",
+        id="test-gateway",
+    )
+
+    # Normal flow: request with full conversation
+    normal_request = HandoffUserInputRequest(
+        conversation=[
+            ChatMessage(role=Role.USER, text="Hello"),
+            ChatMessage(role=Role.ASSISTANT, text="Hi!"),
+        ],
+        awaiting_agent_id="specialist",
+        prompt="Enter input",
+        source_executor_id="test-gateway",
+    )
+
+    # Create mock context
+    mock_ctx = MagicMock()
+    mock_ctx.send_message = AsyncMock()
+
+    # Call resume_from_user with a user response
+    await gateway.resume_from_user(normal_request, "Follow up message", mock_ctx)
+
+    # Verify send_message was called
+    mock_ctx.send_message.assert_called_once()
+
+    # Get the message that was sent
+    call_args = mock_ctx.send_message.call_args
+    sent_message = call_args[0][0]
+
+    # Verify it's a _ConversationWithUserInput
+    assert isinstance(sent_message, _ConversationWithUserInput)
+
+    # Verify it contains the full conversation plus new user message
+    assert len(sent_message.full_conversation) == 3
+    assert sent_message.full_conversation[0].text == "Hello"
+    assert sent_message.full_conversation[1].text == "Hi!"
+    assert sent_message.full_conversation[2].text == "Follow up message"
+
+
+async def test_coordinator_handle_user_input_post_restore():
+    """Test that _HandoffCoordinator.handle_user_input handles post-restore correctly.
+
+    After checkpoint restore, the coordinator has its conversation restored,
+    and the gateway sends only the new user messages. The coordinator should
+    append these to its existing conversation rather than replacing.
+    """
+    from unittest.mock import AsyncMock
+
+    from agent_framework._workflows._handoff import _HandoffCoordinator
+
+    # Create a coordinator with pre-existing conversation (simulating restored state)
+    coordinator = _HandoffCoordinator(
+        starting_agent_id="triage",
+        specialist_ids={"specialist_a": "specialist_a"},
+        input_gateway_id="gateway",
+        termination_condition=lambda conv: False,
+        id="test-coordinator",
+    )
+
+    # Simulate restored conversation
+    coordinator._conversation = [
+        ChatMessage(role=Role.USER, text="Hello"),
+        ChatMessage(role=Role.ASSISTANT, text="Hi there!"),
+        ChatMessage(role=Role.USER, text="Help me"),
+        ChatMessage(role=Role.ASSISTANT, text="Sure, what do you need?"),
+    ]
+
+    # Create mock context
+    mock_ctx = MagicMock()
+    mock_ctx.send_message = AsyncMock()
+
+    # Simulate post-restore: only new user message with explicit flag
+    incoming = _ConversationWithUserInput(
+        full_conversation=[ChatMessage(role=Role.USER, text="I need shipping help")],
+        is_post_restore=True,
+    )
+
+    # Handle the user input
+    await coordinator.handle_user_input(incoming, mock_ctx)
+
+    # Verify conversation was appended, not replaced
+    assert len(coordinator._conversation) == 5
+    assert coordinator._conversation[0].text == "Hello"
+    assert coordinator._conversation[1].text == "Hi there!"
+    assert coordinator._conversation[2].text == "Help me"
+    assert coordinator._conversation[3].text == "Sure, what do you need?"
+    assert coordinator._conversation[4].text == "I need shipping help"
+
+
+async def test_coordinator_handle_user_input_normal_flow():
+    """Test that _HandoffCoordinator.handle_user_input handles normal flow correctly.
+
+    In normal flow (no restore), the gateway sends the full conversation.
+    The coordinator should replace its conversation with the incoming one.
+    """
+    from unittest.mock import AsyncMock
+
+    from agent_framework._workflows._handoff import _HandoffCoordinator
+
+    # Create a coordinator
+    coordinator = _HandoffCoordinator(
+        starting_agent_id="triage",
+        specialist_ids={"specialist_a": "specialist_a"},
+        input_gateway_id="gateway",
+        termination_condition=lambda conv: False,
+        id="test-coordinator",
+    )
+
+    # Set some initial conversation
+    coordinator._conversation = [
+        ChatMessage(role=Role.USER, text="Old message"),
+    ]
+
+    # Create mock context
+    mock_ctx = MagicMock()
+    mock_ctx.send_message = AsyncMock()
+
+    # Normal flow: full conversation including new user message (is_post_restore=False by default)
+    incoming = _ConversationWithUserInput(
+        full_conversation=[
+            ChatMessage(role=Role.USER, text="Hello"),
+            ChatMessage(role=Role.ASSISTANT, text="Hi!"),
+            ChatMessage(role=Role.USER, text="New message"),
+        ],
+        is_post_restore=False,
+    )
+
+    # Handle the user input
+    await coordinator.handle_user_input(incoming, mock_ctx)
+
+    # Verify conversation was replaced (normal flow with full history)
+    assert len(coordinator._conversation) == 3
+    assert coordinator._conversation[0].text == "Hello"
+    assert coordinator._conversation[1].text == "Hi!"
+    assert coordinator._conversation[2].text == "New message"
+
+
+async def test_coordinator_handle_user_input_multiple_consecutive_user_messages():
+    """Test that multiple consecutive USER messages in normal flow are handled correctly.
+
+    This is a regression test for the edge case where a user submits multiple consecutive
+    USER messages. The explicit is_post_restore flag ensures this doesn't get incorrectly
+    detected as a post-restore scenario.
+    """
+    from unittest.mock import AsyncMock
+
+    from agent_framework._workflows._handoff import _HandoffCoordinator
+
+    # Create a coordinator with existing conversation
+    coordinator = _HandoffCoordinator(
+        starting_agent_id="triage",
+        specialist_ids={"specialist_a": "specialist_a"},
+        input_gateway_id="gateway",
+        termination_condition=lambda conv: False,
+        id="test-coordinator",
+    )
+
+    # Set existing conversation with 4 messages
+    coordinator._conversation = [
+        ChatMessage(role=Role.USER, text="Original message 1"),
+        ChatMessage(role=Role.ASSISTANT, text="Response 1"),
+        ChatMessage(role=Role.USER, text="Original message 2"),
+        ChatMessage(role=Role.ASSISTANT, text="Response 2"),
+    ]
+
+    # Create mock context
+    mock_ctx = MagicMock()
+    mock_ctx.send_message = AsyncMock()
+
+    # Normal flow: User sends multiple consecutive USER messages
+    # This should REPLACE the conversation, not append to it
+    incoming = _ConversationWithUserInput(
+        full_conversation=[
+            ChatMessage(role=Role.USER, text="New user message 1"),
+            ChatMessage(role=Role.USER, text="New user message 2"),
+        ],
+        is_post_restore=False,  # Explicit flag - this is normal flow
+    )
+
+    # Handle the user input
+    await coordinator.handle_user_input(incoming, mock_ctx)
+
+    # Verify conversation was REPLACED (not appended)
+    # Without the explicit flag, the old heuristic might incorrectly append
+    assert len(coordinator._conversation) == 2
+    assert coordinator._conversation[0].text == "New user message 1"
+    assert coordinator._conversation[1].text == "New user message 2"
diff --git a/python/samples/getting_started/workflows/checkpoint/handoff_with_tool_approval_checkpoint_resume.py b/python/samples/getting_started/workflows/checkpoint/handoff_with_tool_approval_checkpoint_resume.py
index 8981c1fddd..d9a996e807 100644
--- a/python/samples/getting_started/workflows/checkpoint/handoff_with_tool_approval_checkpoint_resume.py
+++ b/python/samples/getting_started/workflows/checkpoint/handoff_with_tool_approval_checkpoint_resume.py
@@ -122,11 +122,17 @@ def _print_handoff_request(request: HandoffUserInputRequest, request_id: str) ->
     print(f"Awaiting agent: {request.awaiting_agent_id}")
     print(f"Prompt: {request.prompt}")
 
-    print("\nConversation so far:")
-    for msg in request.conversation[-3:]:
-        author = msg.author_name or msg.role.value
-        snippet = msg.text[:120] + "..." if len(msg.text) > 120 else msg.text
-        print(f"  {author}: {snippet}")
+    # Note: After checkpoint restore, conversation may be empty because it's not serialized
+    # to prevent duplication (the conversation is preserved in the coordinator's state).
+    # See issue #2667.
+    if request.conversation:
+        print("\nConversation so far:")
+        for msg in request.conversation[-3:]:
+            author = msg.author_name or msg.role.value
+            snippet = msg.text[:120] + "..." if len(msg.text) > 120 else msg.text
+            print(f"  {author}: {snippet}")
+    else:
+        print("\n(Conversation restored from checkpoint - context preserved in workflow state)")
 
     print(f"{'=' * 60}\n")
 
@@ -273,11 +279,7 @@ async def resume_with_responses(
 
         elif isinstance(event, WorkflowOutputEvent):
             print("\n[Workflow Output Event - Conversation Update]")
-            if (
-                event.data
-                and isinstance(event.data, list)
-                and all(isinstance(msg, ChatMessage) for msg in event.data)
-            ):
+            if event.data and isinstance(event.data, list) and all(isinstance(msg, ChatMessage) for msg in event.data):
                 # Now safe to cast event.data to list[ChatMessage]
                 conversation = cast(list[ChatMessage], event.data)
                 for msg in conversation[-3:]:  # Show last 3 messages