fix(library): include unindexed tracks in missing ReplayGain filter

lib/services/library_database_queue_sql.dart

@@ -7,10 +7,8 @@ String confirmedMissingLyricsSqlPredicate({
   required String lyricsKnownExpr,
 }) => '($lyricsKnownExpr) AND COALESCE($hasLyricsExpr, 0) = 0';
 
-String confirmedMissingReplayGainSqlPredicate({
-  required String hasReplayGainExpr,
-  required String replayGainKnownExpr,
-}) => '($replayGainKnownExpr) AND COALESCE($hasReplayGainExpr, 0) = 0';
+String missingReplayGainSqlPredicate({required String hasReplayGainExpr}) =>
+    'COALESCE($hasReplayGainExpr, 0) = 0';
 
 class _QueueOrderTerm {
   final String column;
@@ -421,8 +419,6 @@ extension _LibraryDbQueueSql on LibraryDatabase {
       hasLyricsExpr: 'h.has_lyrics',
       lyricsKnownExpr: 'COALESCE(h.lyrics_metadata_scan_version, 0) >= 1',
       hasReplayGainExpr: 'h.has_replaygain',
-      replayGainKnownExpr:
-          'COALESCE(h.replaygain_metadata_scan_version, 0) >= 1',
     );
   }
 
@@ -473,8 +469,6 @@ extension _LibraryDbQueueSql on LibraryDatabase {
       lyricsKnownExpr:
           'COALESCE(l.audio_metadata_scan_version, 0) >= ${LibraryDatabase.lyricsMetadataScanVersion}',
       hasReplayGainExpr: 'l.has_replaygain',
-      replayGainKnownExpr:
-          'COALESCE(l.audio_metadata_scan_version, 0) >= ${LibraryDatabase.audioMetadataScanVersion}',
     );
   }
 
@@ -497,7 +491,6 @@ extension _LibraryDbQueueSql on LibraryDatabase {
     required String hasLyricsExpr,
     required String lyricsKnownExpr,
     required String hasReplayGainExpr,
-    required String replayGainKnownExpr,
   }) {
     final quality = request.quality?.trim().toLowerCase();
     if (quality != null && quality.isNotEmpty) {
@@ -593,12 +586,11 @@ extension _LibraryDbQueueSql on LibraryDatabase {
         );
         break;
       case 'missing-replaygain':
-        // Only files whose tags were read since ReplayGain was indexed.
+        // Include legacy rows without indexed ReplayGain as candidates until
+        // a metadata refresh confirms their tags. Requiring a new scan version
+        // hides the entire older collection before it has been rescanned.
         where.add(
-          confirmedMissingReplayGainSqlPredicate(
-            hasReplayGainExpr: hasReplayGainExpr,
-            replayGainKnownExpr: replayGainKnownExpr,
-          ),
+          missingReplayGainSqlPredicate(hasReplayGainExpr: hasReplayGainExpr),
         );
         break;
     }

test/replaygain_library_filter_test.dart

@@ -13,17 +13,13 @@ String _tableDefinition(String path, String table) {
 
 void main() {
   test(
-    'ReplayGain filter excludes unknown rows and follows tag add/remove in both databases',
+    'ReplayGain filter includes unindexed candidates and follows tag add/remove in both databases',
     () async {
-      final historyPredicate = confirmedMissingReplayGainSqlPredicate(
+      final historyPredicate = missingReplayGainSqlPredicate(
         hasReplayGainExpr: 'has_replaygain',
-        replayGainKnownExpr:
-            'COALESCE(replaygain_metadata_scan_version, 0) >= 1',
       );
-      final localPredicate = confirmedMissingReplayGainSqlPredicate(
+      final localPredicate = missingReplayGainSqlPredicate(
         hasReplayGainExpr: 'has_replaygain',
-        replayGainKnownExpr:
-            'COALESCE(audio_metadata_scan_version, 0) >= ${LibraryDatabase.audioMetadataScanVersion}',
       );
       // Use the production table definitions and filter predicates with real
       // SQLite. This catches missing schema columns and NULL/default semantics.
@@ -40,18 +36,22 @@ for table, version, known, predicate in [
     ('library', 'audio_metadata_scan_version', data['scanVersion'], data['localPredicate']),
 ]:
     for name, gain, scanned in [('unknown', 0, 0), ('legacy', 0, known - 1),
-                                ('tagged', 1, known), ('missing', 0, known)]:
+                                ('tagged', 1, known), ('missing', 0, known),
+                                ('legacy-tagged', 1, 0)]:
         db.execute(f'INSERT INTO {table} (id, track_name, artist_name, album_name, file_path, '
                    + ('downloaded_at, service' if table == 'history' else 'scanned_at, source_id')
                    + f', has_replaygain, {version}) VALUES (?, ?, ?, ?, ?, ?, ?, ?, ?)',
                    (name, 'Track', 'Artist', 'Album', '/'+name+'.flac', '2026-01-01', 'test', gain, scanned))
     def matches():
         return [row[0] for row in db.execute(f'SELECT id FROM {table} WHERE {predicate} ORDER BY id')]
-    assert matches() == ['missing'], (table, matches())
+    assert matches() == ['legacy', 'missing', 'unknown'], (table, matches())
     db.execute(f"UPDATE {table} SET has_replaygain = 1 WHERE id = 'missing'")
-    assert matches() == [], (table, matches())
+    assert matches() == ['legacy', 'unknown'], (table, matches())
     db.execute(f"UPDATE {table} SET has_replaygain = 0 WHERE id = 'tagged'")
-    assert matches() == ['tagged'], (table, matches())
+    assert matches() == ['legacy', 'tagged', 'unknown'], (table, matches())
+    # An entirely unindexed collection without ReplayGain must not look empty.
+    db.execute(f'UPDATE {table} SET has_replaygain = 0, {version} = 0')
+    assert len(matches()) == 5, (table, matches())
 print('both databases passed')
 ''',
         jsonEncode({