chore: add state streaming to langgraph example

Author: ranst91

examples/integrations/langgraph-python/apps/agent/main.py

@@ -3,7 +3,7 @@
 It defines the workflow graph, state, tools, nodes and edges.
 """
 
-from copilotkit import CopilotKitMiddleware
+from copilotkit import CopilotKitMiddleware, StateStreamingMiddleware, StateItem
 from langchain.agents import create_agent
 
 # Data & state tools
@@ -17,7 +17,12 @@
 agent = create_agent(
     model="openai:gpt-5.4",
     tools=[query_data, *todo_tools, generate_a2ui, search_flights],
-    middleware=[CopilotKitMiddleware()],
+    middleware=[
+        CopilotKitMiddleware(),
+        StateStreamingMiddleware(
+            StateItem(state_key="todos", tool="manage_todos", tool_argument="todos")
+        ),
+    ],
     state_schema=AgentState,
     system_prompt="""
         You are a polished, professional demo assistant. Keep responses to 1-2 sentences.