fix: cache media cover to avoid vanishing on swipe

app/src/main/java/top/yeij/hearth/media/MediaSessionSource.kt

@@ -38,6 +38,12 @@ class MediaSessionSource(context: Context) {
     // only update in the notification
     private val notificationTitles = mutableMapOf<String, String>()
 
+    // 封面缓存（packageName -> base64）：部分 App 切歌瞬间 ART 为 null，用缓存兜底，
+    // 避免媒体卡横划切换后封面消失
+    // Cover cache (packageName -> base64): some apps briefly return null ART on track
+    // switch; fall back to the cached cover so the card cover doesn't vanish on swipe
+    private val coverCache = mutableMapOf<String, String>()
+
     init {
         HearthNotificationListenerService.onMediaTitle = { pkg, title ->
             notificationTitles[pkg] = title
@@ -222,12 +228,19 @@ class MediaSessionSource(context: Context) {
         val duration = meta?.getLong(MediaMetadata.METADATA_KEY_DURATION) ?: 0L
         val position = state?.position ?: 0L
         val playing = state?.state == PlaybackState.STATE_PLAYING
-        Log.d(TAG, "media: ${c.packageName} duration=$duration position=$position playing=$playing state=${state?.state}")
+        // 封面：优先当前 ART，为空时用缓存兜底（切歌瞬间 ART 可能为 null）
+        // Cover: prefer current ART, fall back to cache when empty (ART may be null
+        // briefly on track switch)
+        val cover = meta?.getBitmap(MediaMetadata.METADATA_KEY_ART)?.let { bitmapToBase64(it) }
+            ?: coverCache[c.packageName]
+            ?: ""
+        if (cover.isNotEmpty()) coverCache[c.packageName] = cover
+        Log.d(TAG, "media: ${c.packageName} duration=$duration position=$position playing=$playing cover=${cover.isNotEmpty()}")
         return MediaInfo(
             title,
             meta?.getString(MediaMetadata.METADATA_KEY_ARTIST) ?: "",
             meta?.getString(MediaMetadata.METADATA_KEY_ALBUM) ?: "",
-            meta?.getBitmap(MediaMetadata.METADATA_KEY_ART)?.let { bitmapToBase64(it) } ?: "",
+            cover,
             playing,
             position,
             duration,