chore(integrations/langgraph-fastapi): sync to langgraph-python reference demo

Author: ranst91

examples/integrations/langgraph-fastapi/agent/main.py

@@ -1,13 +1,24 @@
 import os
 import warnings
+from pathlib import Path
 from dotenv import load_dotenv
+
+# Load .env from the demo project root (one level up from agent/) BEFORE
+# importing src.agent — that import constructs ChatOpenAI at module load,
+# which needs OPENAI_API_KEY in the environment already.
+_demo_root = Path(__file__).parent.parent
+for env_path in (_demo_root / ".env", Path(".env")):
+    if env_path.is_file():
+        load_dotenv(env_path)
+        break
+else:
+    load_dotenv()
+
 from fastapi import FastAPI
 import uvicorn
 from src.agent import graph
 from copilotkit import LangGraphAGUIAgent
 from ag_ui_langgraph import add_langgraph_fastapi_endpoint
-
-_ = load_dotenv()
 app = FastAPI()
 
 

examples/integrations/langgraph-fastapi/agent/pyproject.toml

@@ -15,6 +15,7 @@ dependencies = [
   "fastapi>=0.115.5,<1.0.0",
   "uvicorn>=0.29.0,<1.0.0",
   "python-dotenv>=1.0.0,<2.0.0",
-  "ag-ui-langgraph==0.0.22",
+  "ag-ui-langgraph>=0.0.34",
+  "ag-ui-protocol>=0.1.18",
   "pydantic>=2.0.0,<3.0.0",
 ]

examples/integrations/langgraph-fastapi/agent/src/agent.py

@@ -8,6 +8,7 @@
 from copilotkit import CopilotKitMiddleware, StateStreamingMiddleware, StateItem
 from langchain.agents import create_agent
 from langchain_openai import ChatOpenAI
+from langgraph.checkpoint.memory import MemorySaver
 
 from src.a2ui_dynamic_schema import generate_a2ui
 from src.a2ui_fixed_schema import search_flights
@@ -16,6 +17,10 @@
 
 model = ChatOpenAI(model="gpt-5.4", model_kwargs={"parallel_tool_calls": False})
 
+# FastAPI-specific: langgraph-cli dev supplies its own checkpointer in the
+# reference demo. Here we run under uvicorn + ag-ui-langgraph, so the graph
+# needs an explicit MemorySaver for state/thread persistence within a
+# process.
 agent = create_agent(
     model=model,
     tools=[query_data, *todo_tools, generate_a2ui, search_flights],
@@ -26,6 +31,7 @@
         ),
     ],
     state_schema=AgentState,
+    checkpointer=MemorySaver(),
     system_prompt="""
         You are a polished, professional demo assistant. Keep responses to 1-2 sentences.