fix(client): forward async room handler rejections to onError

[SaifShafi]

Closes #803, for the WebRTCConnection half.

The bug

Two LiveKit room handlers in WebRTCConnection are async, and an emitter discards the promise a handler returns. A rejection therefore became an unhandled rejection rather than reaching the caller.

TrackSubscribed is the one that matters. It awaits audioAdapter.attachRemoteTrack and setupAudioCapture:

this.room.on(RoomEvent.TrackSubscribed, async (track, _publication, participant) => {
  ...
  await this.audioAdapter.attachRemoteTrack(remoteAudioTrack, this.outputDeviceId);
  await this.setupAudioCapture(remoteAudioTrack);

If either fails, the agent's audio never attaches and the consumer is told nothing at all. No error, no disconnect, just silence, which is about the worst shape a failure can take in a voice SDK.

The fix

onError alongside the existing onDebug on BaseConnection, plus a forwardHandlerErrors helper that catches a handler's rejection and reports it. Applied to TrackSubscribed and ActiveSpeakersChanged.

onError is declared on WebRTCConnectionConfig next to onDebug, so the contract is explicit rather than relying on the structural pass-through that currently gets onDebug to the connection.

The helper lives on BaseConnection rather than in WebRTCConnection because #803 says "and potentially others", so the next one is a one-line wrap.

Scope

Only WebRTCConnection. The issue also names scribe.ts streamFromMicrophone, but that already catches internally, calls connection._emitError(error) and closes the connection, so it needs no change. Worth confirming if you had something else in mind there.

Verification

Four tests added. To check they actually detect the bug rather than just passing, I reverted the helper to the previous fire-and-forget behaviour and reran:

test	pre-fix	post-fix
forwards a TrackSubscribed rejection to onError	fail	pass
does not leave the rejection unhandled	fail	pass
forwards an ActiveSpeakersChanged rejection to onError	fail	pass
stays silent when the handler resolves	pass	pass

The last is the negative control and passes either way, by design.

The unhandled-rejection test subscribes to process.on("unhandledRejection") and asserts nothing is emitted, which is the specific symptom the issue describes.

Full client package: prettier, eslint and tsc --noEmit clean, 230 unit tests passing.

Patch changeset included.

[cursor]

PR Summary

Low Risk
Additive optional callback and defensive error routing on the WebRTC event path; happy-path behavior is unchanged aside from caught failures being reported instead of going unhandled.

Overview
Fixes silent WebRTC failures when async LiveKit room handlers reject: LiveKit ignores returned promises, so errors in TrackSubscribed (agent audio attach / capture setup) or ActiveSpeakersChanged used to become unhandled rejections with no app-visible signal.

Adds an optional onError(message, context?) on BaseConnection / WebRTCConnection, plus forwardHandlerErrors to .catch() those async handlers and call it with fixed messages (e.g. "Failed to attach subscribed audio track"). New tests assert forwarding, no unhandled rejections, and no onError on success.

^{Reviewed by Cursor Bugbot for commit eab4441. Bugbot is set up for automated code reviews on this repo. Configure here.}