Cars that turn Bluetooth music off get it through Gearslip, and Spotify's silence is explained

A Skoda, a VW, an Audi and a Bolt all dropped the phone's Bluetooth audio once Android Auto was
up. If Bluetooth audio to the car was connected when it showed Gearslip and drops after, that
car's music goes through Gearslip from then on, remembered per car, and the car screen says so.
Picking Bluetooth by hand clears what was learned. When capture stays silent while Spotify
plays, the car screen says Spotify doesn't let its sound be passed on.

gearslip/src/main/res/values/strings.xml

@@ -875,6 +875,8 @@
     <string name="status_no_car_graphene">The phone is charging, but no car has answered. Check that USB-C port control, under Security &amp; privacy, allows data and isn\'t set to Charging-only.</string>
     <string name="status_stuck_cable">The car hasn\'t shown Gearslip yet. Unplug the cable, wait a few seconds, and plug it back in. If it keeps happening, try another cable or USB port, and share the log in an issue.</string>
     <string name="status_stuck_wireless">The car hasn\'t shown Gearslip yet. Turn the car off and on again, or connect with a cable. If it keeps happening, share the log in an issue.</string>
+    <string name="car_audio_switched">This car turns Bluetooth music off while Gearslip runs, so its music now goes through Gearslip. Allow the prompt on your phone.</string>
+    <string name="car_audio_blocked">%1$s doesn\'t let other apps play its sound, so it can\'t reach the car through Gearslip. Try another music app.</string>
     <string name="bt_address_card_title">Help %1$s know this phone</string>
     <string name="bt_address_card_body">Some cars stay connected only once they know the phone\'s Bluetooth address. Android keeps it from apps, so copy it from About phone. Press and hold the Bluetooth address there, tap Copy, and come back.</string>
     <string name="bt_address_open">Open About phone</string>