Issue: AG-UI Client and ag-ui-adk Incompatibility

[Mikeks81]

I have a feeling this is a me issue as copilotkit was working in their example with the existing "proverbs_agent" but when I followed the documentation to use @ag-ui/client by itself this is what I found and eventually how I got it to work.

Problem Description

The @ag-ui/client JavaScript SDK fails to communicate with agents built using ag-ui-adk Python package, resulting in RUN_ERROR events and failed agent execution.

"use client";
import { useEffect } from "react";
import { HttpAgent } from "@ag-ui/client";

const agent = new HttpAgent({
  url: "http://localhost:8000/",
});

export default function AgUi() {
  useEffect(() => {
    const fetchData = async () => {
      const result = await agent.runAgent({
        messages: [
          {
            id: "msg-1",
            role: "user",
            content: "Hello!",
          },
        ],
      });
      console.log(result.newMessages);
    };
    fetchData();
  }, []);
}

Error Details

Client-Side Error

AGUIError: Cannot send event type 'RUN_FINISHED': The run has already errored with 'RUN_ERROR'. No further events can be sent.

Server-Side Error

ValueError: Both invocation_id and new_message are None.

App Name Mismatch Warning

App name mismatch detected. The runner is configured with app name "proverbs_app", but the root agent was loaded from ".../google/adk/agents", which implies app name "agents".

Package Versions

• @ag-ui/client: 0.0.38
• ag-ui-adk: 0.3.1
• ag-ui-protocol: 0.1.9

Expected Behavior

The AG-UI client should successfully communicate with ADK agents built using ag-ui-adk.

Actual Behavior

The client fails immediately after sending a request, with the agent returning RUN_ERROR due to missing invocation_id and new_message fields.

Request Format Used

{
  "threadId": "test-thread",
  "runId": "test-run", 
  "state": {},
  "messages": [
    {
      "id": "msg-1",
      "role": "user",
      "content": "Hello!"
    }
  ],
  "tools": [],
  "context": [],
  "forwardedProps": {}
}

Workaround

Direct HTTP/SSE calls to the ADKAgent work correctly, bypassing the AG-UI client entirely. This suggests the issue is specifically with the AG-UI client protocol implementation.

Root Cause

There appears to be a protocol mismatch between the event format expected by @ag-ui/client and the format generated by ag-ui-adk. The server-side error indicates that required fields (invocation_id and new_message) are not being properly passed from the client to the agent.

Additional Context

• The ADKAgent itself works correctly when called directly via HTTP/SSE
• The streaming response format is valid and contains proper event types
• The issue occurs specifically when using the @ag-ui/client HttpAgent class

[contextablemark]

@Mikeks81 I'm not sure whether this is "by design" (I'm just another contributor here), but the JavaScript client never forwards the caller’s messages array when invoking HttpAgent.runAgent. RunAgentParameters only allows runId, tools, context, and forwardedProps, and prepareRunAgentInput clones the agent’s internal messages list instead of the messages property the caller passes in, as can be seen here : https://github.com/ag-ui-protocol/ag-ui/blob/main/sdks/typescript/packages/client/src/agent/agent.ts#L144

To get user (or assistant) messages into the payload that HttpAgent.runAgent sends, you have to mutate the agent’s internal messages array before invoking runAgent. The client copies whatever is already in this.messages when it builds the RunAgentInput, so messages you add through addMessage, addMessages, setMessages, or by seeding initialMessages in the constructor are the ones that actually go out on the wire.

[Mikeks81]

@contextablemark , thanks for the reply, references and explanation. I know Copilotkit created and i would think leverages this package but is there documentation or an example on how to use it anywhere? I am hoping to not have to dig through all the code to get a simple POC going before I go all in. Unfortunately, for several reasons, we're not able to leverage CopilotKit at this time. I would love to use the headless functionality but that's experimental at this point. I really like what ag-ui is doing to standardize the FE and Agent interactions and would like to adopt.

[contextablemark]

Understood. Perhaps @NathanTarbert can weigh in.

[NathanTarbert]

Let me defer to @maxkorp or @mme for this

[mme]

@Mikeks81 could you just add the messages to the messages array before calling agent.runAgent?

If you don't want to mutate the original agent, you can clone() it.

[Mdevgaonkar]

@mme I Would like to open a PR with with an updated readme for this. Please assign to me.

[Mikeks81]

@mme I believe my "issue" root cause is that none of the documentation describes how @ag-ui/client should be used. The documentation I did try didn't work as described above. Thanks for the support, and all your work here. I would love if @Mdevgaonkar could update the docs to include how to use this library to send communications to the BE ag-ui AI agent.