perf(metadata): avoid SAF copies during quality probes

lib/providers/download_history_provider.dart

@@ -524,7 +524,10 @@ class DownloadHistoryNotifier extends Notifier<DownloadHistoryState> {
       lookupItems: _lookupItemsWithUpdates([updated]),
     );
     await _db.upsert(updated.toJson());
-    _bumpHistoryRevision();
+    // Swiping through older tracks can backfill several quality records in a
+    // short burst. Coalesce their DB-derived Library refreshes just like
+    // download completion writes instead of rebuilding every view per swipe.
+    _scheduleIndexBump();
   }
 
   Future<void> updateMetadataForItem({

lib/providers/download_history_provider_maintenance.dart

@@ -392,7 +392,7 @@ extension _HistoryStartupMaintenance on DownloadHistoryNotifier {
     }
 
     try {
-      final result = await PlatformBridge.readFileMetadata(filePath);
+      final result = await PlatformBridge.readDisplayAudioMetadata(filePath);
       final error = result['error'];
       if (error != null) {
         if (_isPermanentProbeError(error.toString())) {

lib/screens/track_metadata_screen.dart

@@ -297,7 +297,9 @@ class _TrackMetadataScreenState extends ConsumerState<TrackMetadataScreen>
     _hasLoadedResolvedAudioMetadata = true;
 
     try {
-      final metadata = await PlatformBridge.readFileMetadata(sourcePath);
+      final metadata = await PlatformBridge.readDisplayAudioMetadata(
+        sourcePath,
+      );
       if (!mounted ||
           generation != _metadataLoadGeneration ||
           sourcePath != cleanFilePath) {

lib/services/platform_bridge.dart

@@ -6,6 +6,7 @@ import 'package:flutter/services.dart';
 import 'package:path_provider/path_provider.dart';
 import 'package:shared_preferences/shared_preferences.dart';
 import 'package:spotiflac_android/services/download_request_payload.dart';
+import 'package:spotiflac_android/utils/audio_format_utils.dart';
 import 'package:spotiflac_android/utils/logger.dart';
 
 final _log = AppLogger('PlatformBridge');
@@ -833,6 +834,25 @@ class PlatformBridge {
     return _invokeMap('readFileMetadata', {'file_path': filePath});
   }
 
+  /// Reads the tags and quality fields used for automatic Library display.
+  ///
+  /// Android's readAudioMetadata implementation can inspect most SAF files
+  /// through /proc/self/fd, avoiding the full-file cache copy required by tag
+  /// editing. Keep the complete reader as a compatibility fallback for
+  /// malformed or incorrectly named files that the lightweight scanner could
+  /// only identify from their filename.
+  static Future<Map<String, dynamic>> readDisplayAudioMetadata(
+    String filePath,
+  ) async {
+    final scanned = await readAudioMetadata(filePath);
+    if (scanned != null &&
+        scanned['error'] == null &&
+        scanned['metadataFromFilename'] != true) {
+      return normalizeScannedAudioMetadata(scanned);
+    }
+    return readFileMetadata(filePath);
+  }
+
   static Future<Map<String, dynamic>> editFileMetadata(
     String filePath,
     Map<String, String> metadata,

lib/utils/audio_format_utils.dart

@@ -3,6 +3,39 @@ import 'package:spotiflac_android/utils/string_utils.dart';
 
 /// Audio format/quality helpers shared by the download queue and history
 /// providers.
+Map<String, dynamic> normalizeScannedAudioMetadata(
+  Map<String, dynamic> metadata,
+) {
+  dynamic firstValue(String snakeCase, String camelCase) {
+    final snakeValue = metadata[snakeCase];
+    return snakeValue ?? metadata[camelCase];
+  }
+
+  final normalized = <String, dynamic>{...metadata};
+  final metadataFromFilename = metadata['metadataFromFilename'] == true;
+
+  // readAudioMetadata uses the LibraryScanResult contract. Automatic metadata
+  // probes use the same snake_case keys as readFileMetadata so callers can use
+  // the cheaper SAF file-descriptor path without knowing which backend result
+  // shape was returned.
+  if (!metadataFromFilename) {
+    normalized['title'] = firstValue('title', 'trackName');
+    normalized['artist'] = firstValue('artist', 'artistName');
+    normalized['album'] = firstValue('album', 'albumName');
+  }
+  normalized['album_artist'] = firstValue('album_artist', 'albumArtist');
+  normalized['date'] = firstValue('date', 'releaseDate');
+  normalized['track_number'] = firstValue('track_number', 'trackNumber');
+  normalized['total_tracks'] = firstValue('total_tracks', 'totalTracks');
+  normalized['disc_number'] = firstValue('disc_number', 'discNumber');
+  normalized['total_discs'] = firstValue('total_discs', 'totalDiscs');
+  normalized['bit_depth'] = firstValue('bit_depth', 'bitDepth');
+  normalized['sample_rate'] = firstValue('sample_rate', 'sampleRate');
+  normalized['audio_codec'] =
+      firstValue('audio_codec', 'audioCodec') ?? metadata['format'];
+  return normalized;
+}
+
 int? readPositiveBitrateKbps(dynamic value) {
   final parsed = readPositiveInt(value);
   if (parsed == null) return null;