fix(voice): preserve held STT turn boundaries

[Thytu]

Description

Preserve an accepted STT turn boundary when agent speech starts between the final transcript and its END_OF_SPEECH sentinel.

The final transcript is accepted before agent speech, but the following sentinel is buffered while the agent is speaking. During the later flush, the sentinel has no transcript alternatives, so it cannot set shouldFlush and is discarded. The user turn remains uncommitted and can be merged with later speech.

Changes Made

• Re-emit a held END_OF_SPEECH when STT has accepted transcript text for an uncommitted turn.
• Keep the exception scoped to STT turn detection and buffers that actually contain the pending boundary.
• Add a regression covering the exact final → agent speech → end sentinel → agent speech end ordering.
• Add a patch changeset for @livekit/agents.

Pre-Review Checklist

• Build passes: Full monorepo build and typecheck pass locally
• AI-generated code reviewed: Comments and test setup were reviewed and kept to the state-machine invariant
• Changes explained: The failed transition and bounded exception are documented above
• Scope appropriate: Only held STT turn-boundary handling and its regression are changed
• Video demo: Not applicable; this is an internal event-ordering race covered by a deterministic regression

Testing

• Regression fails on main with userTurnCommitted === false
• Regression passes with the fix
• pnpm test agents/src — 136 files passed; 2,248 tests passed; 5 skipped
• pnpm build
• pnpm typecheck
• pnpm format:check
• pnpm -w lint:fix

Additional Notes

The unscoped test command also runs provider/example integration tests. Locally those reported unrelated missing OPENAI_API_KEY/CEREBRAS_API_KEY, Hugging Face download timeouts, and one FishAudio assertion. The complete agents/src suite passes.

[changeset-bot]

🦋 Changeset detected

Latest commit: 67385f7

The changes in this PR will be included in the next version bump.

This PR includes changesets to release 39 packages

Name	Type
@livekit/agents	Patch
@livekit/agents-plugin-anam	Patch
@livekit/agents-plugin-anthropic	Patch
@livekit/agents-plugin-assemblyai	Patch
@livekit/agents-plugin-azure	Patch
@livekit/agents-plugin-baseten	Patch
@livekit/agents-plugin-bey	Patch
@livekit/agents-plugin-cartesia	Patch
@livekit/agents-plugin-cerebras	Patch
@livekit/agents-plugin-deepgram	Patch
@livekit/agents-plugin-did	Patch
@livekit/agents-plugin-elevenlabs	Patch
@livekit/agents-plugin-fishaudio	Patch
@livekit/agents-plugin-google	Patch
@livekit/agents-plugin-hedra	Patch
@livekit/agents-plugin-hume	Patch
@livekit/agents-plugin-inworld	Patch
@livekit/agents-plugin-krisp	Patch
@livekit/agents-plugin-lemonslice	Patch
@livekit/agents-plugin-liveavatar	Patch
@livekit/agents-plugin-livekit	Patch
@livekit/agents-plugin-minimax	Patch
@livekit/agents-plugin-mistral	Patch
@livekit/agents-plugin-mistralai	Patch
@livekit/agents-plugin-neuphonic	Patch
@livekit/agents-plugin-openai	Patch
@livekit/agents-plugin-perplexity	Patch
@livekit/agents-plugin-phonic	Patch
@livekit/agents-plugin-protoface	Patch
@livekit/agents-plugin-resemble	Patch
@livekit/agents-plugin-rime	Patch
@livekit/agents-plugin-runway	Patch
@livekit/agents-plugin-sarvam	Patch
@livekit/agents-plugin-silero	Patch
@livekit/agents-plugin-soniox	Patch
@livekit/agents-plugin-tavus	Patch
@livekit/agents-plugins-test	Patch
@livekit/agents-plugin-trugen	Patch
@livekit/agents-plugin-xai	Patch

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[devin-ai-integration]

✅ Devin Review: No Issues Found

Devin Review analyzed this PR and found no bugs or issues to report.