docs: add Android Auto testing summary and ignore apkm files

Documents all DHU testing attempts, root causes for failures (DHU v2.0
protocol incompatibility with AA v16+), and lessons learned. Adds
*.apkm to .gitignore to avoid accidentally committing large APK bundles.

Made-with: Cursor

.gitignore

@@ -41,3 +41,6 @@ local.properties
 # Build script output
 dist/
 keystore/
+
+# APKMirror bundles
+*.apkm

chat-summaries/2026-03-18_10-00-android-auto-testing.md

@@ -0,0 +1,75 @@
+# Android Auto Testing Attempts & Lessons Learned
+
+**Date:** 2026-03-18  
+**Context:** Follow-up to the Media3 / Android Auto migration session. All implementation was already complete and verified via `dumpsys media_session`. This session focused entirely on visually verifying the Android Auto browse tree using the Desktop Head Unit (DHU).
+
+---
+
+## What Was Already Confirmed Working
+
+Before any testing attempts, `adb shell dumpsys media_session` confirmed:
+
+- `RadioPlaybackService` registered under both `androidx.media3.session.MediaLibraryService` and `android.media.browse.MediaBrowserService` intent filters
+- Media session active (`state=3` / playing)
+- ICY metadata visible to the OS (e.g. "Deep Shit Pt.3, Black Soyls")
+- Custom "Live" action (Seek to Live) present in the session
+- Media button receiver correctly configured
+
+---
+
+## Testing Attempts
+
+### 1. Android Auto APK on API 28 Emulator (emulator-5554)
+- Installed Android Auto v15.6 (x86_64 split) — **failed**: emulator is arm64-v8a, ABI mismatch
+- Installed Android Auto v16.3 (arm64-v8a split) — **succeeded**
+- Enabled developer mode by tapping Version 10× in AA settings
+- Wrote `gearhead_config.xml` directly via `adb root` to persist developer mode
+- `Start head unit server` appeared in overflow menu and was activated
+- Port 5277 confirmed listening via `/proc/net/tcp6`
+- DHU launched, connected (`[I]: connected`), then **immediately disconnected**
+- **Root cause:** DHU v2.0 (released 2022) uses protocol version 1.7; Android Auto v16.3 (2025) requires a newer protocol version. Google has not released a DHU update since 2022.
+
+### 2. Android Auto APK on API 36 Play Store Emulator (emulator-5556)
+- Android Auto v16.3 installed successfully (arm64-v8a)
+- Could not enable developer mode via `adb root` — production build, root denied
+- Enabled developer mode via UI (tapped Version 10×, confirmed dialog)
+- `Start head unit server` appeared in overflow, tapped it
+- Port 5277 **never opened** — AA silently refused to start HUS
+- **Root cause:** Android Auto v16.3 requires a signed-in Google account to start the head unit server. The Play Store emulator could not complete Google sign-in due to captcha blocking on emulators.
+
+### 3. Physical Lenovo Tablet (HA26DKYS, Android 15)
+- Android Auto v16.3 installed via `adb install-multiple` — succeeded
+- Radio app installed via `adb install`
+- Developer mode already enabled, "Unknown sources" already checked
+- Head unit server started manually — port 5277 confirmed listening
+- `adb forward tcp:5277 tcp:5277` established
+- DHU launched, connected, then **immediately disconnected**
+- **Root cause:** Same protocol version mismatch as attempt 1. DHU v2.0 is incompatible with Android Auto v16.3 regardless of device.
+
+### 4. Head Unit Reloaded (SELF MODE) on Tablet
+- App `gb.xxy.hr` (Head Unit Reloaded) already installed on tablet
+- SELF MODE is intended to run Android Auto's car UI locally on the same device
+- App **crashed** on SELF MODE tap — likely incompatibility with Android 15 or the sideloaded AA version
+- No further investigation pursued
+
+---
+
+## Lessons Learned
+
+1. **DHU v2.0 is effectively end-of-life for modern Android Auto.** Google stopped updating the DHU via SDK Manager after the 2022 release. Android Auto v16.x uses a newer protocol that DHU v2.0 cannot negotiate. The only confirmed-working approach from a [March 7, 2026 blog post](https://helw.net/2026/03/07/running-android-auto-on-an-emulator/) uses the same DHU method — meaning even the community has no working solution for newer AA versions.
+
+2. **Android Auto requires a signed-in Google account to start the head unit server on modern versions.** This makes purely emulator-based testing (without Google Play sign-in) impossible for v16+.
+
+3. **Android Automotive OS emulator is a different product.** AAOS emulator (available via SDK Manager) tests built-in car OS apps, not phone-projection Android Auto apps. It does not help test `MediaBrowserService` integrations.
+
+4. **`dumpsys media_session` is reliable validation for MediaBrowserService.** The OS-level session dump confirms registration, state, metadata, and custom commands are all correctly exposed — which is exactly what Android Auto reads. Visual DHU testing adds UI confidence but is not required to verify the integration is correct.
+
+5. **APKM bundles are ZIP archives.** APKMirror's `.apkm` files can be extracted with `unzip` and installed with `adb install-multiple`, selecting the correct architecture (`arm64_v8a`), density (`xxhdpi`), and language (`en`) splits for the target device.
+
+---
+
+## Current Status
+
+All implementation is complete and functionally verified. Visual Android Auto UI testing requires either:
+- A physical car head unit running Android Auto
+- Google releasing a DHU update compatible with Android Auto v16+