fix(metadata): keep collaboration albums grouped

android/app/src/main/kotlin/com/zarz/spotiflac/NativeDownloadFinalizer.kt

@@ -1068,7 +1068,14 @@ object NativeDownloadFinalizer {
             .put("title", trackString(input, "name", input.request.optString("track_name", "")))
             .put("artist", trackString(input, "artistName", input.request.optString("artist_name", "")))
             .put("album", trackString(input, "albumName", input.request.optString("album_name", "")))
-            .put("album_artist", trackString(input, "albumArtist", input.request.optString("album_artist", "")))
+            .put(
+                "album_artist",
+                NativeFinalizationPolicy.authoritativeAlbumArtist(
+                    requestValue = requestString(input, "album_artist"),
+                    trackValue = trackString(input, "albumArtist", ""),
+                    providerResultValue = resultString(input, "album_artist"),
+                ),
+            )
             .put("track_number", trackInt(input, "trackNumber", input.request.optInt("track_number", 0)))
             .put("disc_number", trackInt(input, "discNumber", input.request.optInt("disc_number", 0)))
             .put("isrc", trackString(input, "isrc", input.request.optString("isrc", "")))
@@ -1229,7 +1236,11 @@ object NativeDownloadFinalizer {
         val albumId = trackString(input, "albumId", "")
         if (albumId.isNotBlank()) return "id:$albumId"
         val albumName = trackString(input, "albumName", input.request.optString("album_name", ""))
-        val albumArtist = trackString(input, "albumArtist", input.request.optString("album_artist", ""))
+        val albumArtist = NativeFinalizationPolicy.authoritativeAlbumArtist(
+            requestValue = requestString(input, "album_artist"),
+            trackValue = trackString(input, "albumArtist", ""),
+            providerResultValue = resultString(input, "album_artist"),
+        )
         return "name:$albumName|$albumArtist"
     }
 
@@ -1248,7 +1259,16 @@ object NativeDownloadFinalizer {
         values.put("track_name", result.optString("title", "").ifBlank { trackString(input, "name", input.request.optString("track_name", "")) })
         values.put("artist_name", result.optString("artist", "").ifBlank { trackString(input, "artistName", input.request.optString("artist_name", "")) })
         values.put("album_name", result.optString("album", "").ifBlank { trackString(input, "albumName", input.request.optString("album_name", "")) })
-        values.put("album_artist", normalizeOptional(resultString(input, "album_artist").ifBlank { trackString(input, "albumArtist", requestString(input, "album_artist")) }))
+        values.put(
+            "album_artist",
+            normalizeOptional(
+                NativeFinalizationPolicy.authoritativeAlbumArtist(
+                    requestValue = requestString(input, "album_artist"),
+                    trackValue = trackString(input, "albumArtist", ""),
+                    providerResultValue = resultString(input, "album_artist"),
+                ),
+            ),
+        )
         values.put("cover_url", normalizeOptional(metadataCoverUrl(input).ifBlank { resultString(input, "cover_url") }))
         values.put("file_path", state.filePath)
         values.put("storage_mode", input.request.optString("storage_mode", "app"))

android/app/src/main/kotlin/com/zarz/spotiflac/NativeFinalizationPolicy.kt

@@ -277,6 +277,22 @@ internal object NativeFinalizationPolicy {
         return if (total > 0) "$number/$total" else number.toString()
     }
 
+    /**
+     * The app request contains the album artist after batch normalization and
+     * user metadata filters. Provider results are only a fallback: preferring
+     * them would reintroduce per-track collaboration credits while finalizing.
+     */
+    fun authoritativeAlbumArtist(
+        requestValue: String?,
+        trackValue: String?,
+        providerResultValue: String?,
+    ): String {
+        return normalizeOptional(requestValue)
+            ?: normalizeOptional(trackValue)
+            ?: normalizeOptional(providerResultValue)
+            ?: ""
+    }
+
     private fun audioFormatForPath(filePath: String, fileName: String): String? {
         for (candidate in listOf(filePath, fileName)) {
             val lower = candidate.trim().lowercase(Locale.ROOT)

android/app/src/main/kotlin/com/zarz/spotiflac/NativeFinalizerMedia.kt

@@ -16,6 +16,7 @@ import com.antonkarpenko.ffmpegkit.ReturnCode
 import com.zarz.spotiflac.SafDownloadHandler.mimeTypeForExt
 import com.zarz.spotiflac.SafDownloadHandler.normalizeExt
 import com.zarz.spotiflac.NativeFinalizationPolicy.applyQualityVariantFilenameLabel
+import com.zarz.spotiflac.NativeFinalizationPolicy.authoritativeAlbumArtist
 import com.zarz.spotiflac.NativeFinalizationPolicy.displayAudioQuality
 import com.zarz.spotiflac.NativeFinalizationPolicy.formatIndexTag
 import com.zarz.spotiflac.NativeFinalizationPolicy.isLosslessAudioCodec
@@ -257,9 +258,11 @@ internal fun NativeDownloadFinalizer.embedBasicMetadata(context: Context, path:
     val album = resultString(input, "album").ifBlank {
         trackString(input, "albumName", requestString(input, "album_name"))
     }
-    val albumArtist = resultString(input, "album_artist").ifBlank {
-        trackString(input, "albumArtist", requestString(input, "album_artist"))
-    }
+    val albumArtist = authoritativeAlbumArtist(
+        requestValue = requestString(input, "album_artist"),
+        trackValue = trackString(input, "albumArtist", ""),
+        providerResultValue = resultString(input, "album_artist"),
+    )
     val date = resultString(input, "release_date").ifBlank {
         resultString(input, "date").ifBlank {
             trackString(input, "releaseDate", requestString(input, "release_date"))

android/app/src/test/kotlin/com/zarz/spotiflac/NativeFinalizationPolicyTest.kt

@@ -96,6 +96,26 @@ class NativeFinalizationPolicyTest {
         )
     }
 
+    @Test
+    fun normalizedRequestAlbumArtistOverridesPerTrackProviderCredits() {
+        assertEquals(
+            "Falling In Reverse",
+            NativeFinalizationPolicy.authoritativeAlbumArtist(
+                requestValue = "Falling In Reverse",
+                trackValue = "Falling In Reverse, Jelly Roll",
+                providerResultValue = "Falling In Reverse, Jelly Roll",
+            ),
+        )
+        assertEquals(
+            "Provider Album Artist",
+            NativeFinalizationPolicy.authoritativeAlbumArtist(
+                requestValue = "",
+                trackValue = null,
+                providerResultValue = "Provider Album Artist",
+            ),
+        )
+    }
+
     @Test
     fun displayQualityUsesMeasuredLosslessSpecifications() {
         assertEquals(