Swappable engine factory. Defaults to createAudioEngine. Override to
wrap the engine with telemetry/audit logging — the documented second consumer
of this boundary token.
Register the override at application bootstrap. The shared engine instance
is itself providedIn: 'root' and is built on first use, so a factory override
registered in a lazy route's providers is never consulted. For a subtree that
needs its own engine, use provideCngxAudioAt(...) in viewProviders.
An override that needs the resolved configuration reads it with
injectAudioConfig (defaults merged); CNGX_AUDIO_DEFAULTS holds
the library baseline. Both are exported from @cngx/common/audio.