default_retry_on re-runs a ToolNode after the server committed (RemoteProtocolError, ReadTimeout, 5xx), duplicating the side effect #9622

import http.server
import json
import threading

import httpx
from langchain_core.messages import AIMessage
from langchain_core.tools import tool
from langgraph.graph import START, MessagesState, StateGraph
from langgraph.prebuilt import ToolNode
from langgraph.types import RetryPolicy

ORDERS = []  # what the order service has committed


class OrderService(http.server.BaseHTTPRequestHandler):
    def do_POST(self):
        body = self.rfile.read(int(self.headers["Content-Length"]))
        ORDERS.append(json.loads(body))  # the order is committed here
        if len(ORDERS) == 1:
            self.close_connection = True  # the reply is lost: close without answering
            return
        self.send_response(200)
        self.send_header("Content-Length", "2")
        self.end_headers()
        self.wfile.write(b"ok")

    def log_message(self, *args):
        pass


server = http.server.HTTPServer(("127.0.0.1", 0), OrderService)
threading.Thread(target=server.serve_forever, daemon=True).start()
URL = f"http://127.0.0.1:{server.server_port}/orders"


@tool
def create_order(sku: str, quantity: int) -> str:
    """Create an order."""
    httpx.post(URL, json={"sku": sku, "quantity": quantity}).raise_for_status()
    return "created"


call = {"name": "create_order", "id": "call-1", "args": {"sku": "A1", "quantity": 1}}
graph = StateGraph(MessagesState)
graph.add_node("tools", ToolNode([create_order]), retry_policy=RetryPolicy())
graph.add_edge(START, "tools")
app = graph.compile()

result = app.invoke({"messages": [AIMessage(content="", tool_calls=[call])]})
print("tool result:", result["messages"][-1].content)
print("orders committed:", len(ORDERS))