Root cause: setBluetoothScoOn(true) is silently rejected on Android 12+
for non-system apps ("is greater than FIRST_APPLICATION_UID exiting").
Audio policy routed to handset instead of BT despite SCO link being up.
Fix: use the modern setCommunicationDevice(AudioDeviceInfo) API on
API 31+ which properly routes voice audio to the BT device. Falls back
to deprecated startBluetoothSco() on older APIs.
Also uses getCommunicationDevice() for is_bluetooth_sco_on() and
clearCommunicationDevice() for stop, matching the modern API surface.
Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>
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