Fake Agent

FakeAgent is an in-process AG-UI AbstractAgent for frontend work when a backend is not ready.

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

#Use the provider

For Angular apps, use provideFakeAgUiAgent().

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

Switching to a real backend is a provider change:

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

#Add reasoning

Pass reasoningTokens when you need to exercise reasoning UI.

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

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

#Configuration

#What it does not do

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

It is 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.