livekit-agents@1.2.8

## Features:

- [AgentSession.start()](https://github.com/livekit/agents/blob/713988e3741a1498d373593c030c0fbd28262284/livekit-agents/livekit/agents/voice/agent_session.py#L401C15-L401C20) now returns a `RunResult` when called with `capture_run=True`.
This makes it possible to assert the first message when the agent initiates the conversation:
```python
result = await sess.start(EchoAgent(), capture_run=True)
result.expect.next_event().is_agent_handoff(new_agent_type=EchoAgent)
result.expect.next_event().is_message(role="assistant")
```

- Agent false interruptions are now automatically resumed after the `false_interruption_timeout`. Audio output is paused and then resumed on the same `SpeechHandle`, eliminating the need to manually call `generate_reply()` in the `agent_false_interruption` event handler—please remove this call if present from earlier versions. This behavior is enabled by default; to disable automatic resume, set `resume_false_interruption=False`.


## What's Changed
* fix: start datastream audio output right after room connected by @longcw in https://github.com/livekit/agents/pull/3270
* add AudioOutput capabilities and disable pause/resume for if output not supported by @longcw in https://github.com/livekit/agents/pull/3269
* fix (11labs): fix empty text input and timeout for the first audio chunk by @longcw in https://github.com/livekit/agents/pull/3284
* chore: switch to gpt-realtime as default OAI realtime model by @davidzhao in https://github.com/livekit/agents/pull/3287
* fix(plugins:elevenlabs): fix exception in STT when serializing bool form field tag_audio_events by @mike-r-mclaughlin in https://github.com/livekit/agents/pull/3282
* primary speaker detection with STT diarization by @longcw in https://github.com/livekit/agents/pull/3186
* add capture_run for AgentSession.start by @longcw in https://github.com/livekit/agents/pull/3288
* chore: add test for empty tts streams by @davidzhao in https://github.com/livekit/agents/pull/3286
* fix say method not being captured by RunResult by @theomonnom in https://github.com/livekit/agents/pull/3291
* support interrupting agent by interim transcripts by @longcw in https://github.com/livekit/agents/pull/3278
* allow SpeechHandle to be interrupted when long-running function tools are pending by @longcw in https://github.com/livekit/agents/pull/3280
* fix: disable false interruption resume for realtime model by @longcw in https://github.com/livekit/agents/pull/3298
* feat(langgraph): support subgraphs in LLMAdapter and normalize astream outputs by @bnovik0v in https://github.com/livekit/agents/pull/3112
* feat: add more llm and stt models to mistralai plugins by @fabitokki in https://github.com/livekit/agents/pull/3300
* chore(langchain): fix types by @davidzhao in https://github.com/livekit/agents/pull/3303

## New Contributors
* @bnovik0v made their first contribution in https://github.com/livekit/agents/pull/3112

**Full Changelog**: https://github.com/livekit/agents/compare/livekit-agents@1.2.7...livekit-agents@1.2.8