Second screen: append the new tiles to existing layouts, not just pristine ones

The first migration only upgraded a layout that was byte-for-byte the old
default, reasoning that anything else was a deliberate arrangement to leave
alone. That fails for the ordinary case: toggle one tile on and off and the
layout is no longer the default, so someone who had barely touched it never
saw the new tiles at all. Which is exactly what happened -- a panel that had
been poked at during testing kept its old contents and looked like the
feature had not shipped.

Now version-stamped and additive: whatever the user arranged stays arranged,
anything missing from the new set is appended, and the stamp means it runs
exactly once -- so removing a tile afterwards sticks.

platforms/android/app/src/main/java/com/armsx2/SecondScreenTiles.kt

@@ -104,23 +104,25 @@ object SecondScreenLayout {
     )
 
     /**
-     * The default as it stood before cover art and the RetroAchievements read-outs existed.
+     * Tiles introduced after the panel shipped, appended once to layouts that predate them.
      *
-     * Kept so the new defaults can reach people who never customised their panel. A saved layout
+     * The first attempt at this only upgraded a layout that was byte-for-byte the old default,
-     * normally wins over DEFAULT -- that is the whole point of saving it -- but a layout that is
+     * on the reasoning that anything else was a deliberate arrangement to leave alone. That
-     * byte-for-byte the OLD default is not a choice anyone made, it is just what they were given.
+     * reasoning fails for the ordinary case: toggle a single tile on and off and the layout is no
-     * Those get upgraded once; anything the user actually arranged is left alone.
+     * longer the default, so a user who had barely touched it never saw the new tiles at all.
+     *
+     * Appending is additive and order-preserving -- whatever the user arranged stays arranged,
+     * the new tiles land at the end, and removing one sticks because the version stamp means this
+     * runs exactly once.
      */
-    private val DEFAULT_V1 = listOf(
+    private const val PREF_LAYOUT_VERSION = "secondScreen.layoutVersion"
-        SecondScreenTile.TITLE,
+    private const val LAYOUT_VERSION = 2
-        SecondScreenTile.FPS,
+
-        SecondScreenTile.BATTERY,
+    private val V2_ADDITIONS = listOf(
-        SecondScreenTile.CLOCK,
+        SecondScreenTile.COVER,
-        SecondScreenTile.SAVE,
+        SecondScreenTile.ACHIEVEMENTS,
-        SecondScreenTile.LOAD,
+        SecondScreenTile.RA_POINTS,
-        SecondScreenTile.FAST_FORWARD,
+        SecondScreenTile.RICH_PRESENCE,
-        SecondScreenTile.PAUSE,
-        SecondScreenTile.SCREENSHOT,
     )
 
     /** Bumped on any change so the panel knows to rebuild and Compose knows to recompose. */
@@ -155,10 +157,19 @@ object SecondScreenLayout {
         runCatching {
             val raw = MainActivityRuntime.prefs.getString(PREF_TILES, null)
             tiles = if (raw == null) DEFAULT else parse(raw)
-            // One-time upgrade for panels still sitting on the untouched old default.
+            val version = MainActivityRuntime.prefs.getInt(PREF_LAYOUT_VERSION, 1)
-            if (tiles == DEFAULT_V1) {
+            if (version < LAYOUT_VERSION) {
-                tiles = DEFAULT
+                // A brand-new panel already has them from DEFAULT; an existing one gets whatever
-                persist()
+                // it is missing appended, exactly once.
+                if (raw != null) {
+                    val missing = V2_ADDITIONS.filterNot { it in tiles }
+                    if (missing.isNotEmpty()) {
+                        tiles = tiles + missing
+                        persist()
+                    }
+                }
+                MainActivityRuntime.prefs.edit()
+                    .putInt(PREF_LAYOUT_VERSION, LAYOUT_VERSION).apply()
             }
             columnCount = MainActivityRuntime.prefs.getInt(PREF_COLUMNS, 3).coerceIn(1, 6)
             tileHeightDp = MainActivityRuntime.prefs.getInt(PREF_TILE_HEIGHT, 0).coerceIn(0, 200)