SerialDevicePresence
Platform-abstracted view of currently-connected serial devices.
Each key is the rest portion of an InterfaceId.SERIAL address (i.e. the address with its leading 's' prefix stripped) — exactly the keys that UsbRepository.serialDevices emits on Android.
Consumed by transport-recovery code (notably SharedRadioInterfaceService.initStateListeners) to detect when a previously-selected serial device has been unplugged and replugged, so the transport can be brought back without manual re-selection.
Platforms without hot-plug observation (e.g. JVM/Desktop jSerialComm) return a perpetually-empty set.