`audio_start` is not called when audio is started

[baseballyama]

Please read this first

• Have you read the docs? Agents SDK docs
• Have you searched for related issues? Others may have faced similar issues.

Describe the bug

https://openai.github.io/openai-agents-js/ja/openai/agents-realtime/type-aliases/realtimesessioneventtypes/#audio_start

On the docs, there is audio_start, but audio_start event is not fired when an audio is start to output.

Debug information

• Agents SDK version: 0.0.12
• Runtime environment Google Chrome Version 138.0.7204.101 (Official Build) (arm64)

Repro steps

Register audio_start event and get audio response.

  import { RealtimeAgent, RealtimeSession } from '@openai/agents-realtime';

  const agent = new RealtimeAgent({
    name: 'Assistant',
    instructions: 'You are an assistant'
  });
  const session = new RealtimeSession(agent, {
    model: 'gpt-4o-realtime-preview-2025-06-03'
  });
  await session.connect({ apiKey: xxx });
  session.on('audio_start', () => {
    console.log('audio_start is called');
  });
  session.sendMessage('Hi!');

Expected behavior

audio_start is called is shown in the console.