diff --git a/SPECS.md b/SPECS.md
index 2767da5..61ee21f 100644
--- a/SPECS.md
+++ b/SPECS.md
@@ -118,6 +118,18 @@ tyre pressures, GPS (lat, lon, elevation, heading) and the is_* flags. It does *
   confirmed car facts, app structure, UI conventions, build/test/ship, documents. It replaces
   upstream's EVABRPUploader text. The test emulator is now in the flake: `nix run .#car-emulator`
   (Android 9 AOSP at 1920×720, 160 dpi; the car build installs as the system user — checked).
+- 2026-10-23 — App 2.19.4: "Export CarPlay data" on the Logs tab (Foreground apps card), for the
+  question whether CarPlay's resolution can change. CarPlay with policy_control still leaves a grey
+  strip, also after reconnecting: Allgo announces a smaller picture to the iPhone. 20 s after the
+  press (time to open CarPlay) it writes to `<stick>/Android/data/<package>/files/
+  nilsmg4-carplay-<time>/` — the only place on a removable volume Android 9 lets an app write:
+  `dumpsys window windows`, `SurfaceFlinger`, `display`, `activity activities`, `wm size/density`,
+  the display-related system properties (identifiers filtered out), Allgo's APK and native
+  libraries, and CarPlay/Allgo/iAP2-named files under /system, /vendor, /odm, /product. It reads
+  the car and writes only to the stick. Owner's choice to export Allgo's software for analysis
+  (2026-10-23). On the emulator (no Allgo there) every dump was written, without permission
+  errors. XDA (leonkernan, page 30) found SAIC's SystemUI hides its top bar itself for a whitelist
+  that includes com.allgo.carplay.service — compiled into SystemUI, not changeable from the app.
 - 2026-10-23 — App 2.19.3: an update log on the Logs tab, above the uploads. A USB install on the
   car ended in an installer message about a broken package, while the same APK installed through
   the Bluetooth-settings route; the message was only a toast and logcat, so its exact words are
diff --git a/app/build.gradle b/app/build.gradle
index 9913f79..05fcd0e 100644
--- a/app/build.gradle
+++ b/app/build.gradle
@@ -34,8 +34,8 @@ android {
         applicationId "com.stinnesbeck.nilsmg4"
         minSdk 27
         targetSdk 36
-        versionCode 102
-        versionName "2.19.3"
+        versionCode 103
+        versionName "2.19.4"
 
         // Nothing about the server ships in the APK: its URL and ingest token are entered in
         // the app's Server tab (ServerConfig), and the database is only reachable by the server.
diff --git a/app/src/main/java/com/evsuite/abrp/CarPlayExport.java b/app/src/main/java/com/evsuite/abrp/CarPlayExport.java
new file mode 100644
index 0000000..a41d0cd
--- /dev/null
+++ b/app/src/main/java/com/evsuite/abrp/CarPlayExport.java
@@ -0,0 +1,234 @@
+package com.evsuite.abrp;
+
+import android.content.Context;
+import android.content.pm.ApplicationInfo;
+import android.os.Environment;
+import android.util.Log;
+
+import java.io.File;
+import java.io.FileInputStream;
+import java.io.FileOutputStream;
+import java.io.IOException;
+import java.io.InputStream;
+import java.io.OutputStream;
+import java.nio.charset.StandardCharsets;
+import java.text.SimpleDateFormat;
+import java.util.ArrayList;
+import java.util.Date;
+import java.util.List;
+import java.util.Locale;
+import java.util.concurrent.TimeUnit;
+import java.util.regex.Pattern;
+
+/**
+ * Read-only diagnostic for the CarPlay resolution question: copies what decides CarPlay's size
+ * to a folder on the USB stick, for reading on a computer. It reads the car and writes only to
+ * the stick.
+ *
+ * What it writes to {@code <stick>/Android/data/<package>/files/nilsmg4-carplay-<time>/}:
+ * <ul>
+ *   <li>the CarPlay app's APK files and its own native libraries;</li>
+ *   <li>libraries and configuration files under /system, /vendor, /odm and /product whose path
+ *       names CarPlay (see {@link #isCarPlayPath});</li>
+ *   <li>the display-related system properties, never identifiers ({@link #keepProperty});</li>
+ *   <li>the window manager, SurfaceFlinger and display state, captured while CarPlay is in front.</li>
+ * </ul>
+ * Only the system user (the car build) may run dumpsys; elsewhere those files say why not.
+ */
+final class CarPlayExport {
+
+    private static final String TAG = "EVABRP.CarPlayExport";
+    static final String CARPLAY_PACKAGE = "com.allgo.carplay.service";
+
+    private static final long MAX_FILE_BYTES = 64L << 20;
+    private static final int MAX_FOUND_FILES = 200;
+    private static final String[] SEARCH_ROOTS = {
+            "/system/etc", "/system/lib", "/system/lib64", "/system/priv-app", "/system/app",
+            "/vendor/etc", "/vendor/lib", "/vendor/lib64", "/vendor/app", "/vendor/priv-app",
+            "/odm/etc", "/product/etc", "/product/app", "/product/priv-app",
+    };
+
+    private static final Pattern CARPLAY_PATH = Pattern.compile("(?i)carplay|allgo|iap2|airplay");
+    private static final Pattern PROPERTY_KEEP = Pattern.compile(
+            "(?i)carplay|allgo|iap|airplay|display|lcd|screen|resolution|density|surface|hwui|"
+                    + "\\bsf\\.|\\.sf\\.|width|height|ro\\.build\\.(version|display|fingerprint|id)|"
+                    + "vehicle_type|projection");
+    private static final Pattern PROPERTY_DROP = Pattern.compile(
+            "(?i)serial|vin\\b|\\.vin|imei|iccid|imsi|mac|bt\\.addr|bdaddr|wifi|ssid|password|token|"
+                    + "key|account|phone|msisdn|sim");
+
+    private CarPlayExport() {}
+
+    /** A path whose name says it belongs to CarPlay. */
+    static boolean isCarPlayPath(String path) {
+        return path != null && CARPLAY_PATH.matcher(path).find();
+    }
+
+    /** A {@code [key]: [value]} getprop line worth exporting: display-related, never an identifier. */
+    static boolean keepProperty(String getpropLine) {
+        if (getpropLine == null) return false;
+        int end = getpropLine.indexOf("]:");
+        String key = end > 0 ? getpropLine.substring(0, end) : getpropLine;
+        return PROPERTY_KEEP.matcher(key).find() && !PROPERTY_DROP.matcher(key).find();
+    }
+
+    /** Runs the export; returns one line for the screen. Blocking: call it off the main thread. */
+    static String run(Context context) {
+        File stick = stickFolder(context);
+        if (stick == null) {
+            Log.w(TAG, "no USB stick");
+            return "No USB stick found";
+        }
+        String stamp = new SimpleDateFormat("yyyyMMdd-HHmmss", Locale.US).format(new Date());
+        File out = new File(stick, "nilsmg4-carplay-" + stamp);
+        if (!out.mkdirs()) {
+            Log.w(TAG, "cannot create " + out);
+            return "Could not create " + out;
+        }
+        List<String> notes = new ArrayList<>();
+        int copied = 0;
+
+        // The live state first, while CarPlay is still in front.
+        command(out, "dumpsys-window.txt", notes, "dumpsys", "window", "windows");
+        command(out, "dumpsys-surfaceflinger.txt", notes, "dumpsys", "SurfaceFlinger");
+        command(out, "dumpsys-display.txt", notes, "dumpsys", "display");
+        command(out, "dumpsys-activity.txt", notes, "dumpsys", "activity", "activities");
+        command(out, "wm.txt", notes, "sh", "-c", "wm size; wm density");
+        properties(out, notes);
+
+        try {
+            ApplicationInfo app = context.getPackageManager().getApplicationInfo(CARPLAY_PACKAGE, 0);
+            notes.add("uid " + app.uid + ", flags 0x" + Integer.toHexString(app.flags)
+                    + ", source " + app.sourceDir + ", native " + app.nativeLibraryDir);
+            File apkDir = new File(out, "apk");
+            copied += copy(new File(app.sourceDir), apkDir, notes);
+            if (app.splitSourceDirs != null) {
+                for (String split : app.splitSourceDirs) copied += copy(new File(split), apkDir, notes);
+            }
+            File[] libs = app.nativeLibraryDir == null ? null : new File(app.nativeLibraryDir).listFiles();
+            if (libs != null) {
+                for (File lib : libs) copied += copy(lib, new File(out, "native"), notes);
+            }
+        } catch (Exception e) {
+            notes.add("CarPlay app not found: " + e);
+        }
+
+        List<File> found = new ArrayList<>();
+        for (String root : SEARCH_ROOTS) find(new File(root), 0, found);
+        for (File f : found) {
+            copied += copy(f, new File(out, "found" + f.getParent()), notes);
+        }
+        notes.add(found.size() + " CarPlay-named files under the system partitions");
+
+        write(new File(out, "notes.txt"), String.join("\n", notes) + "\n");
+        String result = "Exported " + copied + " files to " + out;
+        Log.i(TAG, result);
+        return result;
+    }
+
+    /**
+     * This app's own folder on the removable volume, or on any volume (the emulator) when there is
+     * none: <stick>/Android/data/<package>/files. Android 9 lets an app write there and nowhere
+     * else on a removable volume — the stick's top folder is read-only to it.
+     */
+    private static File stickFolder(Context context) {
+        File fallback = null;
+        for (File dir : context.getExternalFilesDirs(null)) {
+            if (dir == null || UsbVolume.root(dir) == null) continue;
+            boolean removable;
+            try {
+                removable = Environment.isExternalStorageRemovable(dir);
+            } catch (IllegalArgumentException e) {
+                removable = false;
+            }
+            if (removable) return dir;
+            if (fallback == null) fallback = dir;
+        }
+        return fallback;
+    }
+
+    private static void find(File dir, int depth, List<File> found) {
+        if (depth > 5 || found.size() >= MAX_FOUND_FILES) return;
+        File[] entries = dir.listFiles();
+        if (entries == null) return;
+        for (File f : entries) {
+            if (found.size() >= MAX_FOUND_FILES) return;
+            if (f.isDirectory()) {
+                if (isCarPlayPath(f.getName())) {
+                    File[] inner = f.listFiles();
+                    if (inner != null) for (File g : inner) if (g.isFile()) found.add(g);
+                }
+                find(f, depth + 1, found);
+            } else if (isCarPlayPath(f.getName())) {
+                found.add(f);
+            }
+        }
+    }
+
+    private static void properties(File out, List<String> notes) {
+        String all = exec(notes, "getprop");
+        if (all == null) return;
+        StringBuilder kept = new StringBuilder();
+        for (String line : all.split("\n")) if (keepProperty(line)) kept.append(line).append('\n');
+        write(new File(out, "properties.txt"), kept.toString());
+    }
+
+    private static void command(File out, String name, List<String> notes, String... argv) {
+        String text = exec(notes, argv);
+        if (text != null) write(new File(out, name), text);
+    }
+
+    private static String exec(List<String> notes, String... argv) {
+        Process p = null;
+        try {
+            p = new ProcessBuilder(argv).redirectErrorStream(true).start();
+            p.getOutputStream().close();
+            byte[] bytes = readAll(p.getInputStream(), 8 << 20);
+            if (!p.waitFor(20, TimeUnit.SECONDS)) notes.add(String.join(" ", argv) + ": timed out");
+            return new String(bytes, StandardCharsets.UTF_8);
+        } catch (Exception e) {
+            notes.add(String.join(" ", argv) + ": " + e);
+            return null;
+        } finally {
+            if (p != null) p.destroy();
+        }
+    }
+
+    private static int copy(File source, File dir, List<String> notes) {
+        if (!source.isFile()) return 0;
+        if (source.length() > MAX_FILE_BYTES) {
+            notes.add("skipped (too large): " + source + " " + source.length());
+            return 0;
+        }
+        if (!dir.isDirectory() && !dir.mkdirs()) {
+            notes.add("no folder for " + source);
+            return 0;
+        }
+        try (InputStream in = new FileInputStream(source);
+             OutputStream os = new FileOutputStream(new File(dir, source.getName()))) {
+            byte[] buffer = new byte[64 * 1024];
+            int n;
+            while ((n = in.read(buffer)) != -1) os.write(buffer, 0, n);
+            return 1;
+        } catch (IOException e) {
+            notes.add("not copied: " + source + ": " + e.getMessage());
+            return 0;
+        }
+    }
+
+    private static byte[] readAll(InputStream in, int max) throws IOException {
+        java.io.ByteArrayOutputStream buffer = new java.io.ByteArrayOutputStream();
+        byte[] chunk = new byte[16 * 1024];
+        int n;
+        while ((n = in.read(chunk)) != -1 && buffer.size() < max) buffer.write(chunk, 0, n);
+        return buffer.toByteArray();
+    }
+
+    private static void write(File file, String text) {
+        try (OutputStream os = new FileOutputStream(file)) {
+            os.write(text.getBytes(StandardCharsets.UTF_8));
+        } catch (IOException e) {
+            Log.w(TAG, "not written: " + file, e);
+        }
+    }
+}
diff --git a/app/src/main/java/com/evsuite/abrp/MainActivity.java b/app/src/main/java/com/evsuite/abrp/MainActivity.java
index 7b25a6b..a34a28b 100644
--- a/app/src/main/java/com/evsuite/abrp/MainActivity.java
+++ b/app/src/main/java/com/evsuite/abrp/MainActivity.java
@@ -242,9 +242,46 @@ public class MainActivity extends AppCompatActivity {
         if (r.statusBarPx != null) {
             sb.append('\n').append(getString(R.string.foreground_status_bar, r.statusBarPx));
         }
+        if (lastCarPlayExport != null) {
+            sb.append('\n').append(getString(R.string.carplay_export_last, lastCarPlayExport));
+        }
         return sb.toString();
     }
 
+    /** The last CarPlay export's outcome, for the Foreground apps card; null before the first. */
+    private static volatile String lastCarPlayExport;
+
+    /**
+     * Waits 20 seconds, so the driver can bring CarPlay to the front, then exports what decides
+     * its size to the USB stick (CarPlayExport). Runs in the app's process, which the upload
+     * service keeps alive while this activity is in the background.
+     */
+    private void startCarPlayExport() {
+        android.content.Context app = getApplicationContext();
+        android.os.Handler main = new android.os.Handler(android.os.Looper.getMainLooper());
+        Toast.makeText(app, R.string.carplay_export_started, Toast.LENGTH_LONG).show();
+        new Thread(() -> {
+            try {
+                Thread.sleep(20_000);
+            } catch (InterruptedException e) {
+                return;
+            }
+            main.post(() -> Toast.makeText(app, R.string.carplay_export_running, Toast.LENGTH_SHORT).show());
+            String result;
+            try {
+                result = CarPlayExport.run(app);
+            } catch (Throwable t) {
+                result = "Export failed: " + t;
+            }
+            lastCarPlayExport = result;
+            final String shown = result;
+            main.post(() -> {
+                Toast.makeText(app, shown, Toast.LENGTH_LONG).show();
+                refreshForeground();
+            });
+        }, "carplay-export").start();
+    }
+
     /** Refreshes state + call log while the screen is visible. */
     private final android.os.Handler uiHandler = new android.os.Handler(android.os.Looper.getMainLooper());
     private final Runnable uiRefresh = new Runnable() {
@@ -298,6 +335,7 @@ public class MainActivity extends AppCompatActivity {
         logPane.findViewById(R.id.flush_now_button).setOnClickListener(v -> manualFlush());
         foregroundText = logPane.findViewById(R.id.foreground_text);
         logPane.findViewById(R.id.foreground_refresh_button).setOnClickListener(v -> refreshForeground());
+        logPane.findViewById(R.id.carplay_export_button).setOnClickListener(v -> startCarPlayExport());
 
         setUpPager();
         // Back on the page that was open when the activity was recreated (accent colour change).
diff --git a/app/src/main/java/com/evsuite/abrp/UsbVolume.java b/app/src/main/java/com/evsuite/abrp/UsbVolume.java
new file mode 100644
index 0000000..e8b73ed
--- /dev/null
+++ b/app/src/main/java/com/evsuite/abrp/UsbVolume.java
@@ -0,0 +1,23 @@
+package com.evsuite.abrp;
+
+import java.io.File;
+
+/** Where the top folder of a storage volume is, found without a file picker (the head unit has none). */
+final class UsbVolume {
+
+    private UsbVolume() { }
+
+    /**
+     * The top folder of the volume an app-specific folder lives on:
+     * /storage/1234-ABCD/Android/data/<package>/files → /storage/1234-ABCD. Null when the path
+     * does not have that shape.
+     */
+    static File root(File appFilesDir) {
+        if (appFilesDir == null) return null;
+        File data = appFilesDir.getParentFile() == null ? null : appFilesDir.getParentFile().getParentFile();
+        File android = data == null ? null : data.getParentFile();
+        if (!"files".equals(appFilesDir.getName()) || data == null || !"data".equals(data.getName())
+                || android == null || !"Android".equals(android.getName())) return null;
+        return android.getParentFile();
+    }
+}
diff --git a/app/src/main/res/layout-w1000dp/pane_log.xml b/app/src/main/res/layout-w1000dp/pane_log.xml
index 2050239..8c3392e 100644
--- a/app/src/main/res/layout-w1000dp/pane_log.xml
+++ b/app/src/main/res/layout-w1000dp/pane_log.xml
@@ -10,6 +10,7 @@
         <LinearLayout android:layout_width="0dp" android:layout_weight="1" android:layout_height="wrap_content" android:orientation="vertical" android:paddingStart="24dp" android:paddingEnd="24dp" android:paddingTop="16dp" android:paddingBottom="16dp" android:background="@drawable/bg_glass">
             <LinearLayout android:layout_width="match_parent" android:layout_height="wrap_content" android:orientation="horizontal" android:gravity="center_vertical">
                 <TextView android:layout_width="0dp" android:layout_weight="1" android:layout_height="wrap_content" android:text="@string/foreground_title" android:textAppearance="@style/Text.EV.Eyebrow" />
+                <com.google.android.material.button.MaterialButton android:id="@+id/carplay_export_button" style="@style/Widget.EV.Button.Outlined" android:layout_width="wrap_content" android:layout_height="48dp" android:layout_marginEnd="8dp" android:minWidth="0dp" android:paddingStart="16dp" android:paddingEnd="16dp" android:text="@string/btn_carplay_export" />
                 <com.google.android.material.button.MaterialButton android:id="@+id/foreground_refresh_button" style="@style/Widget.EV.Button.Outlined" android:layout_width="48dp" android:layout_height="48dp" android:minWidth="0dp" android:padding="0dp" android:contentDescription="@string/btn_refresh" app:icon="@drawable/ic_refresh" app:iconGravity="textStart" app:iconPadding="0dp" app:iconTint="?attr/evAccent" />
             </LinearLayout>
             <TextView android:layout_width="match_parent" android:layout_height="wrap_content" android:layout_marginTop="4dp" android:text="@string/foreground_hint" android:textAppearance="@style/Text.EV.Secondary" />
diff --git a/app/src/main/res/layout/pane_log.xml b/app/src/main/res/layout/pane_log.xml
index 863c052..ebe5749 100644
--- a/app/src/main/res/layout/pane_log.xml
+++ b/app/src/main/res/layout/pane_log.xml
@@ -9,6 +9,7 @@
         <LinearLayout android:layout_width="match_parent" android:layout_height="wrap_content" android:orientation="vertical" android:padding="24dp" android:background="@drawable/bg_glass" android:layout_marginTop="16dp">
             <LinearLayout android:layout_width="match_parent" android:layout_height="wrap_content" android:orientation="horizontal" android:gravity="center_vertical">
                 <TextView android:layout_width="0dp" android:layout_weight="1" android:layout_height="wrap_content" android:text="@string/foreground_title" android:textAppearance="@style/Text.EV.Eyebrow" />
+                <com.google.android.material.button.MaterialButton android:id="@+id/carplay_export_button" style="@style/Widget.EV.Button.Outlined" android:layout_width="wrap_content" android:layout_height="48dp" android:layout_marginEnd="8dp" android:minWidth="0dp" android:paddingStart="16dp" android:paddingEnd="16dp" android:text="@string/btn_carplay_export" />
                 <com.google.android.material.button.MaterialButton android:id="@+id/foreground_refresh_button" style="@style/Widget.EV.Button.Outlined" android:layout_width="48dp" android:layout_height="48dp" android:minWidth="0dp" android:padding="0dp" android:contentDescription="@string/btn_refresh" app:icon="@drawable/ic_refresh" app:iconGravity="textStart" app:iconPadding="0dp" app:iconTint="?attr/evAccent" />
             </LinearLayout>
             <TextView android:layout_width="match_parent" android:layout_height="wrap_content" android:layout_marginTop="4dp" android:text="@string/foreground_hint" android:textAppearance="@style/Text.EV.Secondary" />
diff --git a/app/src/main/res/values/strings.xml b/app/src/main/res/values/strings.xml
index 3030f4c..863e66e 100644
--- a/app/src/main/res/values/strings.xml
+++ b/app/src/main/res/values/strings.xml
@@ -174,6 +174,10 @@
     <string name="update_log_title">Updates, newest first:</string>
     <string name="btn_flush_now">Upload now</string>
     <string name="foreground_title">Foreground apps</string>
+    <string name="btn_carplay_export">Export CarPlay data</string>
+    <string name="carplay_export_started">Open CarPlay now: the export to the USB stick starts in 20 seconds</string>
+    <string name="carplay_export_running">Exporting CarPlay data to the USB stick…</string>
+    <string name="carplay_export_last">Last export: %1$s</string>
     <string name="foreground_hint">For the CarPlay full-screen test: open CarPlay, come back here, read its name off the list. Reads only.</string>
     <string name="foreground_recent">Last 30 minutes, newest first:</string>
     <string name="foreground_none">No app came to the front in the last 30 minutes.</string>
diff --git a/app/src/test/java/com/evsuite/abrp/CarPlayExportTest.java b/app/src/test/java/com/evsuite/abrp/CarPlayExportTest.java
new file mode 100644
index 0000000..290e1b9
--- /dev/null
+++ b/app/src/test/java/com/evsuite/abrp/CarPlayExportTest.java
@@ -0,0 +1,43 @@
+package com.evsuite.abrp;
+
+import static org.junit.Assert.assertFalse;
+import static org.junit.Assert.assertTrue;
+
+import org.junit.Test;
+
+/** What the CarPlay export takes along — pure JVM. */
+public class CarPlayExportTest {
+
+    @Test
+    public void displayPropertiesAreKept() {
+        assertTrue(CarPlayExport.keepProperty("[ro.sf.lcd_density]: [160]"));
+        assertTrue(CarPlayExport.keepProperty("[persist.allgo.carplay.height]: [640]"));
+        assertTrue(CarPlayExport.keepProperty("[ro.build.mtk2712.vehicle_type]: [AS28]"));
+        assertTrue(CarPlayExport.keepProperty("[ro.build.display.id]: [SWI68-29958-1300R69]"));
+    }
+
+    @Test
+    public void identifiersNeverLeave() {
+        assertFalse(CarPlayExport.keepProperty("[ro.serialno]: [ABC123]"));
+        assertFalse(CarPlayExport.keepProperty("[persist.vehicle.vin]: [LSJ...]"));
+        assertFalse(CarPlayExport.keepProperty("[persist.carplay.wifi.ssid]: [MG4-1234]"));
+        assertFalse(CarPlayExport.keepProperty("[persist.carplay.bt.addr]: [00:11:22:33:44:55]"));
+        assertFalse(CarPlayExport.keepProperty("[ro.boot.serialno]: [x]"));
+        assertFalse(CarPlayExport.keepProperty(null));
+    }
+
+    @Test
+    public void unrelatedPropertiesStay() {
+        assertFalse(CarPlayExport.keepProperty("[dalvik.vm.heapsize]: [512m]"));
+        assertFalse(CarPlayExport.keepProperty("[persist.sys.timezone]: [Europe/Berlin]"));
+    }
+
+    @Test
+    public void carPlayPathsAreRecognised() {
+        assertTrue(CarPlayExport.isCarPlayPath("/vendor/etc/allgo/config.xml"));
+        assertTrue(CarPlayExport.isCarPlayPath("libCarPlayCore.so"));
+        assertTrue(CarPlayExport.isCarPlayPath("iap2_config.ini"));
+        assertFalse(CarPlayExport.isCarPlayPath("/system/etc/hosts"));
+        assertFalse(CarPlayExport.isCarPlayPath(null));
+    }
+}
diff --git a/app/src/unstable/java/com/evsuite/abrp/UsbUpdate.java b/app/src/unstable/java/com/evsuite/abrp/UsbUpdate.java
index 5697180..037f301 100644
--- a/app/src/unstable/java/com/evsuite/abrp/UsbUpdate.java
+++ b/app/src/unstable/java/com/evsuite/abrp/UsbUpdate.java
@@ -16,19 +16,9 @@ final class UsbUpdate {
 
     private UsbUpdate() { }
 
-    /**
-     * The top folder of the volume an app-specific folder lives on:
-     * /storage/1234-ABCD/Android/data/<package>/files → /storage/1234-ABCD. Null when the path
-     * does not have that shape. This is how a stick is found without a file picker, which the
-     * head unit does not have.
-     */
+    /** The top folder of the volume [appFilesDir] lives on; see {@link UsbVolume#root}. */
     static File volumeRoot(File appFilesDir) {
-        if (appFilesDir == null) return null;
-        File data = appFilesDir.getParentFile() == null ? null : appFilesDir.getParentFile().getParentFile();
-        File android = data == null ? null : data.getParentFile();
-        if (!"files".equals(appFilesDir.getName()) || data == null || !"data".equals(data.getName())
-                || android == null || !"Android".equals(android.getName())) return null;
-        return android.getParentFile();
+        return UsbVolume.root(appFilesDir);
     }
 
     /**