Pre-warming the record engine at launch was forcing AirPods Pro (and any BT headset that was the system-default input) into bidirectional voice mode — locked the output to 24 kHz stereo, killed the 48 kHz music profile, and produced FaceTime-call sound quality even though no recording was happening. The user heard the degraded audio every minute they wore AirPods. `defaultInputIsBluetooth()` reads the system default input's transport type via CoreAudio's `kAudioDevicePropertyTransportType`. When it's Bluetooth or BTLE, skip the prewarm so the BT device stays in music mode. Cost: first record-key press on a BT mic pays ~50–200 ms of AVAudioEngine cold-start. Wired / built-in mics still prewarm so recording feels instant where the trade-off doesn't apply. Co-Authored-By: Claude Opus 4.7 <noreply@anthropic.com>