Long-text streaming synthesis (useStreamSpeech) with early playback that begins before synthesis completes, a live clause counter + current-clause display, speed control (0.5x–2.0x), pause/resume/stop transport, a WAV download (audio-{voiceId}-{timestamp}.wav), a one-shot single-take synthesis path, a 10,000-character limit with pre-flight validation, and one-click sample texts. Kokoro downloads only on the first synthesize/stream action. Fully on-device. Split from ui/blocks/audio-studio (Audiobook tab).