OptionalschedulerSchedules refresh (defaults to setTimeout); tests can stub.
OptionalsessionBuilds the session client (defaults to the real fetch-based one).
OptionaltransportBuilds the transport (defaults to RuntimeWidgetTransport; tests inject a mock). May be async (the default lazy-loads).
OptionalvoiceBuilds the voice controller for voice-enabled instances (defaults to RealtimeVoiceController). May be async (the default lazy-loads).
Optional injection points so the loader is unit-testable without a network/runtime.