diff --git a/backend/packages/harness/deerflow/agents/middlewares/view_image_middleware.py b/backend/packages/harness/deerflow/agents/middlewares/view_image_middleware.py
index 2870624c3..37432cd9a 100644
--- a/backend/packages/harness/deerflow/agents/middlewares/view_image_middleware.py
+++ b/backend/packages/harness/deerflow/agents/middlewares/view_image_middleware.py
@@ -1,22 +1,19 @@
 """Middleware for injecting image details into conversation before LLM call."""
 
 import logging
-from typing import NotRequired, override
+from typing import override
 
-from langchain.agents import AgentState
 from langchain.agents.middleware import AgentMiddleware
 from langchain_core.messages import AIMessage, HumanMessage, ToolMessage
 from langgraph.runtime import Runtime
 
-from deerflow.agents.thread_state import ViewedImageData
+from deerflow.agents.thread_state import ThreadState
 
 logger = logging.getLogger(__name__)
 
 
-class ViewImageMiddlewareState(AgentState):
-    """Compatible with the `ThreadState` schema."""
-
-    viewed_images: NotRequired[dict[str, ViewedImageData] | None]
+class ViewImageMiddlewareState(ThreadState):
+    """Reuse the thread state so reducer-backed keys keep their annotations."""
 
 
 class ViewImageMiddleware(AgentMiddleware[ViewImageMiddlewareState]):
diff --git a/backend/tests/test_create_deerflow_agent.py b/backend/tests/test_create_deerflow_agent.py
index 2b6c74370..03fee2055 100644
--- a/backend/tests/test_create_deerflow_agent.py
+++ b/backend/tests/test_create_deerflow_agent.py
@@ -1,11 +1,14 @@
 """Tests for create_deerflow_agent SDK entry point."""
 
+from typing import get_type_hints
 from unittest.mock import MagicMock, patch
 
 import pytest
 
 from deerflow.agents.factory import create_deerflow_agent
 from deerflow.agents.features import Next, Prev, RuntimeFeatures
+from deerflow.agents.middlewares.view_image_middleware import ViewImageMiddleware
+from deerflow.agents.thread_state import ThreadState
 
 
 def _make_mock_model():
@@ -127,6 +130,13 @@ def test_vision_injects_view_image_tool(mock_create_agent):
     assert "view_image" in tool_names
 
 
+def test_view_image_middleware_preserves_viewed_images_reducer():
+    middleware_hints = get_type_hints(ViewImageMiddleware.state_schema, include_extras=True)
+    thread_hints = get_type_hints(ThreadState, include_extras=True)
+
+    assert middleware_hints["viewed_images"] == thread_hints["viewed_images"]
+
+
 # ---------------------------------------------------------------------------
 # 8. Subagent feature auto-injects task_tool
 # ---------------------------------------------------------------------------