How do I get my (f-droid or locally built) Android app to show up in the Android Auto launcher?

I am attempting to add Android Auto support to this open source audio recorder app. According to this page, all I need to do is add:

<meta-data
    android:name="com.google.android.gms.car.application"
    android:resource="@xml/automotive_app_desc"/>

And set the minSdkVersion to 23. I've done this, and created app/src/main/res/xml/automotive_app_desc.xml with the following contents:

<?xml version="1.0" encoding="utf-8"?>
<automotiveApp>
    <uses name="media"/>
</automotiveApp>

I've also enabled Developer Mode in my Android Auto app, and I have "Unknown Sources" checked, but when I send a debug build of the app to my phone and plug my phone into my car, it doesn't show up.

By contrast, when I do a local build of AntennaPod, the debug version shows up just fine.

When I open up Android Auto and expand the "Version and Permissions Info", I get this:

Packages:
Audio Recorder: 3.5.15debug
AntennaPod: 3.0.2
AntennaPod Debug: 2.5.2
Maps: 11.77.0300
Google Play Store: 35.8.12-21 [0] [PR] 531622345
Messages: 10.1.40.41
Google Play services: 23.16.13 (100400-527363516)
Android Auto: 9.3.631434-release
... (more apps)

Permissions:
phone: on
contacts: on
location: on
sms: on
microphone: on
calendar: on
call_log: on
nearby_devices: off

Where (more apps) expands to a list of the apps on my phone that show up in the Android Auto Launcher, so it seems that "Audio Recorder" is somehow registered with Android Auto, it's just not being displayed.

I thought this might be something to do with signing keys, but that seems unlikely given that I never set up any sort of signing keys for AntennaPod.

Have you also implemented a MediaBrowserService and added the corresponding manifest declarations for it?