Three fixes for Bluetooth audio not working:
1. is_bluetooth_available() now checks for TYPE_BLUETOOTH_A2DP (8) in
addition to TYPE_BLUETOOTH_SCO (7) — many headsets only register as
A2DP until SCO is explicitly started.
2. set_bluetooth_sco(on=true) polls isBluetoothScoOn() for up to 3s
before restarting Oboe. startBluetoothSco() is async — the SCO link
takes 500ms-2s to establish. Without waiting, Oboe opens against
earpiece and audio goes nowhere.
3. Frontend skips redundant set_speakerphone(false) when transitioning
to BT — start_bluetooth_sco() handles speaker-off internally,
avoiding a double Oboe restart.
Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>
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