fix(download): publish converted SAF files with the final extension

lib/providers/download_queue_provider_single_item.dart

@@ -1002,13 +1002,14 @@ class _DownloadRun {
         (localFile.uri.pathSegments.isEmpty
             ? 'track$safOutputExt'
             : localFile.uri.pathSegments.last);
-    final localExt = n._downloadResultOutputExt(result, filePath: localPath);
-    if (localExt != null && localExt.isNotEmpty) {
-      finalName = finalName.replaceFirst(RegExp(r'\.[^.]+$'), localExt);
-      if (!finalName.toLowerCase().endsWith(localExt.toLowerCase())) {
-        finalName = '$finalName$localExt';
-      }
-    }
+    finalName = finalizedAudioFileName(
+      fileName: finalName,
+      localPath: localPath,
+      fallbackExtension:
+          n._downloadResultOutputExt(result, filePath: localPath) ??
+          safOutputExt,
+    );
+    final localExt = finalName.substring(finalName.lastIndexOf('.'));
 
     final measured = probedFinalMetadata;
     final qualityLabel = buildQualityVariantFilenameLabel(
@@ -1039,7 +1040,11 @@ class _DownloadRun {
     String? publishedName;
     var alreadyExists = false;
     if (item.preserveQualityVariant && qualityVariantCollisionOnly) {
-      final logicalName = safFileName ?? finalName;
+      final logicalName = finalizedAudioFileName(
+        fileName: safFileName ?? finalName,
+        localPath: localPath,
+        fallbackExtension: localExt,
+      );
       final stagingLabel = qualityVariantStagingLabel(item.id);
       final cleanName = removeQualityVariantStagingLabel(
         fileName: logicalName,
@@ -1057,7 +1062,7 @@ class _DownloadRun {
         relativeDir: effectiveOutputDir,
         cleanFileName: cleanName,
         variantFileName: variantName,
-        mimeType: n._mimeTypeForExt(localExt ?? safOutputExt),
+        mimeType: n._mimeTypeForExt(localExt),
         srcPath: localPath,
         preservedSuffix: qualityLabel ?? '',
       );
@@ -1068,7 +1073,7 @@ class _DownloadRun {
         treeUri: settings.downloadTreeUri,
         relativeDir: effectiveOutputDir,
         fileName: finalName,
-        mimeType: n._mimeTypeForExt(localExt ?? safOutputExt),
+        mimeType: n._mimeTypeForExt(localExt),
         srcPath: localPath,
         preservedSuffix: qualityLabel ?? '',
       );
@@ -1079,7 +1084,7 @@ class _DownloadRun {
         treeUri: settings.downloadTreeUri,
         relativeDir: effectiveOutputDir,
         fileName: finalName,
-        mimeType: n._mimeTypeForExt(localExt ?? safOutputExt),
+        mimeType: n._mimeTypeForExt(localExt),
         srcPath: localPath,
       );
       publishedUri = published?.uri;

lib/utils/audio_format_utils.dart

@@ -134,6 +134,23 @@ String isoBmffAudioExtensionForCodec(String? codec) {
   return normalizeAudioFormatValue(codec) == 'ac4' ? '.mp4' : '.m4a';
 }
 
+/// Uses the finalized local container after conversion, before publishing to
+/// SAF. Provider output fields still describe the original download here.
+String finalizedAudioFileName({
+  required String fileName,
+  required String localPath,
+  required String fallbackExtension,
+}) {
+  final extension =
+      RegExp(
+        r'\.(flac|m4a|mp4|mp3|opus|ogg|aac|wav|aiff)$',
+        caseSensitive: false,
+      ).firstMatch(localPath)?.group(0)?.toLowerCase() ??
+      fallbackExtension;
+  final stem = fileName.replaceFirst(RegExp(r'\.[^.]+$'), '');
+  return '$stem$extension';
+}
+
 /// Resolves the actual audio codec reported by native metadata probing, while
 /// falling back to the container format when the codec is absent or generic.
 ///

test/models_and_utils_test.dart

@@ -23,6 +23,47 @@ import 'package:spotiflac_android/utils/path_match_keys.dart';
 import 'package:spotiflac_android/utils/string_utils.dart';
 
 void main() {
+  group('Finalized SAF audio names', () {
+    for (final extension in ['mp3', 'opus', 'flac', 'ogg', 'm4a', 'mp4']) {
+      test(
+        'publishes the final $extension container instead of source M4A',
+        () {
+          expect(
+            finalizedAudioFileName(
+              fileName: 'Example song.m4a',
+              localPath: '/cache/final_audio.$extension',
+              fallbackExtension: '.m4a',
+            ),
+            'Example song.$extension',
+          );
+        },
+      );
+    }
+    test('preserves variant labels and normalizes uppercase suffixes', () {
+      expect(
+        finalizedAudioFileName(
+          fileName: 'Song [OPUS 256kbps].m4a',
+          localPath: '/cache/final.OPUS',
+          fallbackExtension: '.m4a',
+        ),
+        'Song [OPUS 256kbps].opus',
+      );
+    });
+    test(
+      'uses the reported container when the temporary path has no suffix',
+      () {
+        expect(
+          finalizedAudioFileName(
+            fileName: 'Song',
+            localPath: '/cache/final_audio',
+            fallbackExtension: '.m4a',
+          ),
+          'Song.m4a',
+        );
+      },
+    );
+  });
+
   group('file deletion', () {
     test('confirms a local file is absent before reporting success', () async {
       final tempDir = await Directory.systemTemp.createTemp(