The car is not somewhere you can sideload an app into

Android Auto's Unknown sources setting covers media, messaging and
parked apps; it has never covered the Car App Library, so the README's
advice to turn it on could not have worked. A head unit lists DriverVault
only when Play was the installer — an internal track is enough — and the
Desktop Head Unit is what takes a sideloaded build. Say that instead, and
say which APK the DHU wants, since only a debug build allows its host.

minCarApiLevel also claimed a floor lower than the screens stand on:
GarageScreen asks for ConstraintManager, which is level 2.

Co-Authored-By: Claude Opus 5 <noreply@anthropic.com>

Phone App/README.md

@@ -295,15 +295,23 @@ Running it on your own car:
 - The service is declared under `androidx.car.app.category.IOT`. It is the
   closest of the categories the library defines — DriverVault is a garage, not a
   map, a media player or a parking service — and a Play Store submission would
-  be reviewed against it. This build is sideloaded, so what matters instead is
-  the next line.
-- Android Auto refuses apps it did not get from the Play Store until you tell it
-  otherwise: in the **Android Auto** settings on the phone, tap the version ten
-  times to unlock **Developer settings**, then turn on **Unknown sources**.
-- To try it without a car, run Google's
-  [Desktop Head Unit](https://developer.android.com/training/cars/testing/dhu).
-  A debug build accepts any host so the DHU can connect; a release build only
-  accepts the signed hosts the library ships an allowlist for.
+  be reviewed against it. Getting it onto a car at all is the next line.
+- **A sideloaded build never appears on a real head unit**, and no setting on the
+  phone changes that. Android Auto's **Unknown sources** developer option is the
+  one everybody reaches for here, but it covers media, messaging-notification and
+  parked apps only — [Google's testing
+  guide](https://developer.android.com/training/cars/testing) says in as many
+  words that it does not apply to apps built with the Car App Library. A car will
+  list DriverVault only if the APK was installed *from Play*: an internal testing
+  track, or internal app sharing, is enough — no public listing, no review.
+- To try it without Play — which is how these screens were written — run Google's
+  [Desktop Head Unit](https://developer.android.com/training/cars/testing/dhu),
+  which does take a sideloaded build. In the **Android Auto** settings on the
+  phone, tap the version ten times to unlock **Developer settings**, then
+  **Start head unit server**; on the machine, `adb forward tcp:5277 tcp:5277` and
+  run `desktop-head-unit`. Install the **debug** APK for this: a debug build
+  accepts any host so the DHU can connect, while a release build only accepts the
+  signed hosts the library ships an allowlist for.
 
 ## Configure the API endpoint
 

Phone App/android/app/src/main/AndroidManifest.xml

@@ -50,9 +50,13 @@
         <meta-data
             android:name="com.google.android.gms.car.application"
             android:resource="@xml/automotive_app_desc"/>
+        <!-- Level 2, not 1: GarageScreen asks the host for ConstraintManager to
+             size its list, and that service arrived at level 2. Every shipping
+             host is far above this; the floor just has to not claim less than
+             the screens actually use. -->
         <meta-data
             android:name="androidx.car.app.minCarApiLevel"
-            android:value="1"/>
+            android:value="2"/>
         <service
             android:name=".car.DriverVaultCarAppService"
             android:exported="true">