Fake Agent

FakeAgent is an in-process AG-UI AbstractAgent for frontend work when the backend isn't ready yet.

It emits a canned stream:

1. RUN_STARTED
2. optional REASONING_MESSAGE_*
3. TEXT_MESSAGE_START
4. one TEXT_MESSAGE_CONTENT event per token
5. TEXT_MESSAGE_END
6. RUN_FINISHED

It's for demos, story-like development, and tests. It's not a production transport.

#Use the provider

For Angular apps, use provideFakeAgent().

import { ApplicationConfig } from '@angular/core';
import { provideFakeAgent } from '@threadplane/ag-ui';
 
export const appConfig: ApplicationConfig = {
  providers: [
    provideFakeAgent({
      tokens: ['Hello', ' from', ' a', ' fake', ' agent.'],
      delayMs: 50,
    }),
  ],
};

Your component stays the same as the real backend version:

import { Component } from '@angular/core';
import { ChatComponent } from '@threadplane/chat';
import { injectAgent } from '@threadplane/ag-ui';
 
@Component({
  standalone: true,
  imports: [ChatComponent],
  template: `<chat [agent]="agent" />`,
})
export class DemoChat {
  protected readonly agent = injectAgent();
}

Switching to a real backend is a provider change:

- provideFakeAgent({ tokens: ['Offline', ' response.'] })
+ provideAgent({ url: '/api/agent' })

#Add reasoning

Pass reasoningTokens when you need to exercise reasoning UI.

provideFakeAgent({
  reasoningTokens: ['Reading policy. ', 'Checking account status.'],
  tokens: ['The account is eligible.'],
  delayMs: 40,
});

Reasoning events are emitted before text events and use the same message id, so the reducer stores reasoning and final content on one assistant message.

#Use the class directly

Use FakeAgent directly when a test needs an AG-UI source rather than Angular DI.

import { FakeAgent, toAgent } from '@threadplane/ag-ui';
 
const source = new FakeAgent({
  tokens: ['One', ' two', ' three.'],
  delayMs: 1,
});
 
const agent = toAgent(source);

That gives you the same Agent contract as provideFakeAgent().

#Configuration

#What it does not do

FakeAgent does not call a model, execute tools, persist history, or simulate interrupts.

It's deliberately small. Use it to keep UI work moving, not to validate backend behavior.

For backend integration, test against your real AG-UI endpoint and the event map in Event Mapping.