publish(audioTrack:to:options:)

func publish(audioTrack: LocalAudioTrack, to participant: RemoteParticipant, options: AudioPublishOptions? = nil) async throws -> LocalTrackPublication

Discussion

建立 AudioConverter 發送 pipeline：MicrophoneCapturer output → fill(pcmBuffer) → Float32→Int16 + MTU 分包 → RevueKitBridge.sendAudioFrame。

每位好友最多一路音訊：核心層每個 friendId 只有一路 Opus 音訊（AAC 暫不使用）。 已對這位好友發布過音訊時，再次 publish 會 throw RoomError.audioPublicationAlreadyExists， 舊的發布保留不變；要換軌道，先 unpublish(publication:) 舊的再 publish 新的。

let mixForA = AudioCompositor()
mixForA.addTrack(localParticipant.microphoneTrack)
if let audioOfB = participantB.firstAudioTrack { mixForA.addTrack(audioOfB) }
try await localParticipant.publish(audioTrack: mixForA.outputTrack, to: participantA)