Python: [Python]: AG-UI workflow server fails to respond after initial client message

[moonbox3]

Discussed in #6914

^{Originally posted by wigging July 5, 2026}
I'm trying to figure out how to interact with a multi-agent workflow that is served with AG-UI. My server code is shown below which is based on the example in the Agent Framework docs.

# server.py

from textwrap import dedent

import uvicorn
from agent_framework import Agent, Message, Workflow
from agent_framework_ag_ui import add_agent_framework_fastapi_endpoint
from agent_framework_ag_ui import AgentFrameworkWorkflow
from agent_framework.openai import OpenAIChatClient
from agent_framework.orchestrations import HandoffBuilder
from dotenv import load_dotenv
from fastapi import FastAPI


def create_agents() -> tuple:
    """Create agents for the workflow."""
    chat_client = OpenAIChatClient(model="gpt-5.5")

    triage_agent = Agent(
        client=chat_client,
        name="triage_agent",
        instructions=dedent("""\
        You are the triage agent.

        Decide whether the user needs one of these specialist agents:
        - math_agent: arithmetic, calculations, equations, or math explanations.
        - writing_agent: rewrite, summarize, edit, or improve text.
        - code_agent: Python, programming, debugging, or software development questions.

        Hand off to the best agent. Do not answer the task yourself.
        """),
        require_per_service_call_history_persistence=True,
    )

    math_agent = Agent(
        client=chat_client,
        name="math_agent",
        instructions=(
            "You solve math and calculation problems. Return the answer clearly. "
            "Do not hand off unless the user asks for a different kind of help."
        ),
        require_per_service_call_history_persistence=True,
    )

    writing_agent = Agent(
        client=chat_client,
        name="writing_agent",
        instructions=(
            "You rewrite, summarize, edit, and improve text. Return the improved text clearly. "
            "Do not hand off unless the user asks for a different kind of help."
        ),
        require_per_service_call_history_persistence=True,
    )

    code_agent = Agent(
        client=chat_client,
        name="code_agent",
        instructions=(
            "You answer Python, programming, debugging, and software development questions. "
            "Do not hand off unless the user asks for a different kind of help."
        ),
        require_per_service_call_history_persistence=True,
    )

    return triage_agent, math_agent, writing_agent, code_agent


def termination_condition(conversation: list[Message]) -> bool:
    for msg in reversed(conversation):
        if msg.role == "assistant" and (msg.text or "").strip().lower().endswith(
            "case complete."
        ):
            return True
    return False


def create_workflow() -> Workflow:
    """Create a handoff workflow."""
    triage_agent, math_agent, writing_agent, code_agent = create_agents()

    builder = HandoffBuilder(
        name="handoff",
        participants=[triage_agent, math_agent, writing_agent, code_agent],
        termination_condition=termination_condition,
    )
    builder.add_handoff(triage_agent, [math_agent, writing_agent, code_agent])
    builder.with_start_agent(triage_agent)

    return builder.build()


def main():
    """Run the server."""
    load_dotenv()

    workflow = AgentFrameworkWorkflow(
        workflow_factory=lambda _thread_id: create_workflow(),
        name="workflow",
        description="Example of a handoff workflow.",
    )

    app = FastAPI(title="AG-UI Workflow Server")
    add_agent_framework_fastapi_endpoint(app, workflow)

    uvicorn.run(app)


if __name__ == "__main__":
    main()

My client code is shown next. It connects to the AG-UI server which I'm running locally on port 8000. This client code works fine when I serve a single agent and I can send several user messages in the same session without problems. But I'm having issues when the server is for a workflow.

# client.py

import asyncio

from agent_framework import Agent
from agent_framework_ag_ui import AGUIChatClient


async def main():
    """Run the client."""
    server_url = "http://127.0.0.1:8000/"
    chat_client = AGUIChatClient(endpoint=server_url)

    agent = Agent(
        name="Client Agent",
        client=chat_client,
        instructions="you are a helpful assistant",
    )

    thread = agent.create_session()

    try:
        while True:
            # Get user input
            message = input("\nUser (:q or quit to exit): ")
            if not message.strip():
                print("Request cannot be empty.")
                continue

            if message.lower() in (":q", "quit"):
                break

            # Stream the agent response
            print("\nAssistant: ", end="", flush=True)
            async for update in agent.run(message, session=thread, stream=True):
                # Print text content as it streams
                if update.text:
                    print(f"\033[96m{update.text}\033[0m", end="", flush=True)

            print("\n")
    except KeyboardInterrupt:
        print("\n\nExiting...")
    except Exception as e:
        print(f"\n\033[91mAn error occurred: {e}\033[0m")


if __name__ == "__main__":
    asyncio.run(main())

This works for the initial user message (prompt) but subsequent messages fail on the server. The error given below is from the server after the second message is sent.

agent_framework.exceptions.ChatClientException:
("<class 'agent_framework_openai._chat_client.OpenAIChatClient'> service failed to complete the prompt:
Error code: 400 - {'error': {'message': 'No tool output found for function call 0c9a1ef3-ba95-4ae6-9d11-7fbab624bdd9.',
'type': 'invalid_request_error', 'param': 'input', 'code': None}}",
BadRequestError("Error code: 400 - {'error': {'message': 'No tool output found for function call 0c9a1ef3-ba95-4ae6-9d11-7fbab624bdd9.', 'type': 'invalid_request_error', 'param': 'input', 'code': None}}"))

I can't find much information in the Agent Framework docs regarding the client side code for multi-agent workflows. How am I supposed to interact with an AG-UI workflow server? Does the client code need to use an ID or something else to connect with the workflow? This was fairly straightforward with a single agent but seems to be more involved with workflows.

[wigging]

Just leaving a comment in here to remind myself to track this issue since it was moved from the Discussions section.