refactor(metadata): reuse the platform tag mapper

lib/screens/track_metadata_convert.dart

@@ -104,58 +104,6 @@ extension _TrackMetadataConvertAndCueSplit on _TrackMetadataScreenState {
     };
   }
 
-  Map<String, String> _mapMetadataForTagEmbed(Map<String, dynamic> source) {
-    final mapped = <String, String>{};
-
-    void put(String key, dynamic value) {
-      final normalized = value?.toString().trim();
-      if (normalized == null || normalized.isEmpty) return;
-      mapped[key] = normalized;
-    }
-
-    put('TITLE', source['title']);
-    put('ARTIST', source['artist']);
-    put('ALBUM', source['album']);
-    put('ALBUMARTIST', source['album_artist']);
-    put('DATE', source['date']);
-    put('ISRC', source['isrc']);
-    put('GENRE', source['genre']);
-    put('ORGANIZATION', source['label']);
-    put('COPYRIGHT', source['copyright']);
-    put('COMPOSER', source['composer']);
-    put('COMMENT', source['comment']);
-    put('LYRICS', source['lyrics']);
-    put('UNSYNCEDLYRICS', source['lyrics']);
-    if (parseExplicitFlag(source['explicit']) == true) {
-      mapped['ITUNESADVISORY'] = '1';
-    }
-
-    final trackNumber = source['track_number'];
-    final totalTracks = source['total_tracks'];
-    if (trackNumber != null && trackNumber.toString() != '0') {
-      final trackTag =
-          totalTracks != null &&
-              totalTracks.toString().isNotEmpty &&
-              totalTracks.toString() != '0'
-          ? '${trackNumber.toString()}/${totalTracks.toString()}'
-          : trackNumber;
-      put('TRACKNUMBER', trackTag);
-    }
-    final discNumber = source['disc_number'];
-    final totalDiscs = source['total_discs'];
-    if (discNumber != null && discNumber.toString() != '0') {
-      final discTag =
-          totalDiscs != null &&
-              totalDiscs.toString().isNotEmpty &&
-              totalDiscs.toString() != '0'
-          ? '${discNumber.toString()}/${totalDiscs.toString()}'
-          : discNumber;
-      put('DISCNUMBER', discTag);
-    }
-
-    return mapped;
-  }
-
   String? _extractLossyBitrateLabel(String? quality) {
     if (quality == null || quality.isEmpty) return null;
     final match = RegExp(

lib/screens/track_metadata_lyrics.dart

@@ -528,7 +528,9 @@ extension _TrackMetadataLyricsAndSaving on _TrackMetadataScreenState {
         try {
           final result = await PlatformBridge.readFileMetadata(workingPath);
           if (result['error'] == null) {
-            final mapped = _mapMetadataForTagEmbed(result);
+            // Map separately so a non-explicit file keeps the fallback advisory.
+            final mapped = <String, String>{};
+            mergePlatformMetadataForTagEmbed(target: mapped, source: result);
             metadata.addAll(mapped);
           }
         } catch (e) {

test/track_metadata_lyrics_test.dart

@@ -1,4 +1,5 @@
 import 'dart:convert';
+import 'dart:io';
 
 import 'package:flutter/material.dart';
 import 'package:flutter/services.dart';
@@ -15,6 +16,158 @@ void main() {
   final messenger =
       TestDefaultBinaryMessengerBinding.instance.defaultBinaryMessenger;
 
+  for (final fallbackExplicit in [false, true]) {
+    for (final fileExplicit in <bool?>[true, false, null]) {
+      testWidgets(
+        'lyrics embed preserves tags with fallback explicit=$fallbackExplicit '
+        'and file explicit=$fileExplicit',
+        (tester) async {
+          SharedPreferences.setMockInitialValues({});
+          tester.view.physicalSize = const Size(1000, 2400);
+          tester.view.devicePixelRatio = 1;
+          addTearDown(tester.view.resetPhysicalSize);
+          addTearDown(tester.view.resetDevicePixelRatio);
+          const path = 'content://library/document/song.opus';
+          final workingPath = '${Directory.systemTemp.path}/lyrics-test.opus';
+          const lyrics = '[00:01.00]Fresh online lyrics';
+          List<String>? embedArguments;
+          const ffmpeg = MethodChannel('flutter.arthenica.com/ffmpeg_kit');
+          const events = MethodChannel(
+            'flutter.arthenica.com/ffmpeg_kit_event',
+          );
+          const paths = MethodChannel('plugins.flutter.io/path_provider');
+          messenger.setMockMethodCallHandler(paths, (_) async {
+            return Directory.systemTemp.path;
+          });
+          messenger.setMockMethodCallHandler(events, (_) async => null);
+          messenger.setMockMethodCallHandler(ffmpeg, (call) async {
+            if (call.method == 'ffmpegSession') {
+              embedArguments = List<String>.from(
+                (call.arguments as Map)['arguments'] as List,
+              );
+              // Inspect the real embed command without writing an audio file.
+              throw PlatformException(code: 'captured_embed');
+            }
+            return null;
+          });
+          messenger.setMockMethodCallHandler(channel, (call) async {
+            switch (call.method) {
+              case 'safStat':
+                return jsonEncode({'exists': true, 'size': 100});
+              case 'readAudioMetadata':
+              case 'getSafFileModTimes':
+                return '{}';
+              case 'safCopyToTemp':
+                return workingPath;
+              case 'extractCoverToFile':
+                return jsonEncode({'error': 'No cover'});
+              case 'getLyricsLRCWithSource':
+                final online = (call.arguments as Map)['file_path'] == '';
+                return jsonEncode({
+                  'lyrics': online ? lyrics : '',
+                  'source': online ? 'Example Lyrics' : '',
+                });
+              case 'readFileMetadata':
+                if ((call.arguments as Map)['file_path'] != workingPath) {
+                  return '{}';
+                }
+                return jsonEncode({
+                  'title': ' File title ',
+                  'artist': ' First Artist; Second Artist ',
+                  'album': ' ',
+                  'album_artist': ' Album Artist ',
+                  'date': ' 2026-01-02 ',
+                  'isrc': ' EXAMPLE12345 ',
+                  'genre': ' Genre ',
+                  'label': ' Label ',
+                  'copyright': ' Copyright ',
+                  'composer': ' Composer ',
+                  'comment': ' Comment ',
+                  'lyrics': 'Old embedded lyrics',
+                  'track_number': 2,
+                  'total_tracks': 12,
+                  'disc_number': 1,
+                  'total_discs': 3,
+                  'explicit': fileExplicit,
+                });
+              default:
+                return null;
+            }
+          });
+          addTearDown(() {
+            for (final mocked in [channel, ffmpeg, events, paths]) {
+              messenger.setMockMethodCallHandler(mocked, null);
+            }
+          });
+          await tester.pumpWidget(
+            ProviderScope(
+              child: MaterialApp(
+                localizationsDelegates: AppLocalizations.localizationsDelegates,
+                supportedLocales: AppLocalizations.supportedLocales,
+                home: TrackMetadataScreen(
+                  item: DownloadHistoryItem(
+                    id: 'lyrics-song',
+                    trackName: 'Fallback title',
+                    artistName: 'Fallback artist',
+                    albumName: 'Fallback album',
+                    filePath: path,
+                    service: 'example-provider',
+                    downloadedAt: DateTime(2026),
+                    format: 'opus',
+                    explicit: fallbackExplicit,
+                  ),
+                ),
+              ),
+            ),
+          );
+          await tester.pumpAndSettle();
+          await tester.ensureVisible(find.text('Fetch from Online'));
+          await tester.tap(find.text('Fetch from Online'));
+          await tester.pumpAndSettle();
+          expect(find.text('Fresh online lyrics'), findsOneWidget);
+          await tester.ensureVisible(find.text('Embed Lyrics'));
+          await tester.tap(find.text('Embed Lyrics'));
+          // Allow real filesystem cleanup after the mocked native boundary.
+          await tester.runAsync(() async {
+            for (var i = 0; i < 100 && embedArguments == null; i++) {
+              await Future<void>.delayed(const Duration(milliseconds: 10));
+            }
+            await Future<void>.delayed(const Duration(milliseconds: 50));
+          });
+          await tester.pumpAndSettle();
+          expect(embedArguments, isNotNull);
+          final tags = <String, String>{};
+          for (var i = 0; i < embedArguments!.length - 1; i++) {
+            if (embedArguments![i] != '-metadata') continue;
+            final tag = embedArguments![i + 1];
+            final separator = tag.indexOf('=');
+            tags[tag.substring(0, separator)] = tag.substring(separator + 1);
+          }
+          expect(tags, {
+            'TITLE': 'File title',
+            'ARTIST': 'First Artist; Second Artist',
+            'ALBUM': 'Fallback album',
+            'ALBUMARTIST': 'Album Artist',
+            'DATE': '2026-01-02',
+            'YEAR': '2026',
+            'ISRC': 'EXAMPLE12345',
+            'GENRE': 'Genre',
+            'ORGANIZATION': 'Label',
+            'COPYRIGHT': 'Copyright',
+            'COMPOSER': 'Composer',
+            'COMMENT': 'Comment',
+            'TRACKNUMBER': '2/12',
+            'DISCNUMBER': '1/3',
+            'LYRICS': lyrics,
+            'UNSYNCEDLYRICS': lyrics,
+            if (fallbackExplicit || fileExplicit == true) 'ITUNESADVISORY': '1',
+          });
+          expect(tester.takeException(), isNull);
+        },
+      );
+    }
+  }
+
   for (final scenario in [
     'fallback',
     'local',