Idle-suspend window bumped from 2 s to 60 s so the audio engine stays warm between phrases. The first note after every short pause used to pay a 50–100 ms `engine.start()` cold-start cost (audible as "sometimes the piano is slow on the first hit"); now every keystroke in a session lands with the same latency. Adds a compact speaker icon + slider at the popover's top-left that scales every backend (GM / sampler / radio / sample voice / plugin) together via `preLimiterMixer.outputVolume`. Click the speaker to mute; click again restores the prior value. Persisted to UserDefaults. Also requests a 128-frame IO buffer on engine start as a defensive lower bound (honored when Menu Band is the sole client of the output device). Hog-mode helpers landed but stay dormant — AVAudioEngine re-asserts 512 frames even with `kAudioDevicePropertyHogMode` held, so we'd pay the "other audio apps go silent" cost without the latency win; left in for a future AUHAL-direct backend that can exploit it. Co-Authored-By: Claude Opus 4.7 <noreply@anthropic.com>