EngineState

Engine lifecycle, mirroring the underlying AudioContext: - `cold` — no context yet, or a failed unlock. - `unlocking` — a resume() is in flight. - `live` — the context is running. - `suspended` — the context was paused, normally by `autoPauseOnHidden` on tab hide. Recoverable with `unlock()` . - `interrupted` — iOS took the audio session (phone call, Siri). `resume()` does not recover from this; the OS has to hand it back. - `closed` — terminal.