perf(metadata): avoid SAF copies during quality probes

test/models_and_utils_test.dart

@@ -792,6 +792,53 @@ void main() {
   });
 
   group('audio conversion utils', () {
+    test('normalizes lightweight library scan metadata for display probes', () {
+      final normalized = normalizeScannedAudioMetadata({
+        'trackName': 'Song',
+        'artistName': 'Artist',
+        'albumName': 'Album',
+        'albumArtist': 'Album Artist',
+        'releaseDate': '2026',
+        'trackNumber': 2,
+        'totalTracks': 10,
+        'discNumber': 1,
+        'totalDiscs': 2,
+        'bitDepth': 24,
+        'sampleRate': 96000,
+        'bitrate': 1840,
+        'format': 'flac',
+      });
+
+      expect(normalized['title'], 'Song');
+      expect(normalized['artist'], 'Artist');
+      expect(normalized['album'], 'Album');
+      expect(normalized['album_artist'], 'Album Artist');
+      expect(normalized['date'], '2026');
+      expect(normalized['track_number'], 2);
+      expect(normalized['total_tracks'], 10);
+      expect(normalized['disc_number'], 1);
+      expect(normalized['total_discs'], 2);
+      expect(normalized['bit_depth'], 24);
+      expect(normalized['sample_rate'], 96000);
+      expect(normalized['bitrate'], 1840);
+      expect(normalized['audio_codec'], 'flac');
+    });
+
+    test('does not replace stored tags with filename scan fallbacks', () {
+      final normalized = normalizeScannedAudioMetadata({
+        'trackName': 'Filename fallback',
+        'artistName': 'Unknown Artist',
+        'albumName': 'Unknown Album',
+        'metadataFromFilename': true,
+        'format': 'flac',
+      });
+
+      expect(normalized['title'], isNull);
+      expect(normalized['artist'], isNull);
+      expect(normalized['album'], isNull);
+      expect(normalized['audio_codec'], 'flac');
+    });
+
     test('distinguishes an ALAC codec from its M4A container', () {
       expect(normalizeAudioFormatValue('ALAC'), 'alac');
       expect(

test/platform_bridge_metadata_test.dart

@@ -0,0 +1,78 @@
+import 'dart:convert';
+
+import 'package:flutter/services.dart';
+import 'package:flutter_test/flutter_test.dart';
+import 'package:spotiflac_android/services/platform_bridge.dart';
+
+void main() {
+  TestWidgetsFlutterBinding.ensureInitialized();
+  const backendChannel = MethodChannel('com.zarz.spotiflac/backend');
+
+  tearDown(() async {
+    TestDefaultBinaryMessengerBinding.instance.defaultBinaryMessenger
+        .setMockMethodCallHandler(backendChannel, null);
+  });
+
+  test('display metadata uses the lightweight scan result directly', () async {
+    final invokedMethods = <String>[];
+    TestDefaultBinaryMessengerBinding.instance.defaultBinaryMessenger
+        .setMockMethodCallHandler(backendChannel, (call) async {
+          invokedMethods.add(call.method);
+          if (call.method == 'readAudioMetadata') {
+            return jsonEncode({
+              'trackName': 'Song',
+              'artistName': 'Artist',
+              'bitDepth': 24,
+              'sampleRate': 96000,
+              'bitrate': 1800,
+              'format': 'flac',
+            });
+          }
+          fail('Unexpected full metadata read: ${call.method}');
+        });
+
+    final result = await PlatformBridge.readDisplayAudioMetadata(
+      'content://downloads/song.flac',
+    );
+
+    expect(invokedMethods, ['readAudioMetadata']);
+    expect(result['title'], 'Song');
+    expect(result['artist'], 'Artist');
+    expect(result['bit_depth'], 24);
+    expect(result['sample_rate'], 96000);
+    expect(result['audio_codec'], 'flac');
+  });
+
+  test(
+    'display metadata falls back when scan only parsed the filename',
+    () async {
+      final invokedMethods = <String>[];
+      TestDefaultBinaryMessengerBinding.instance.defaultBinaryMessenger
+          .setMockMethodCallHandler(backendChannel, (call) async {
+            invokedMethods.add(call.method);
+            if (call.method == 'readAudioMetadata') {
+              return jsonEncode({
+                'trackName': 'Filename fallback',
+                'metadataFromFilename': true,
+                'format': 'flac',
+              });
+            }
+            if (call.method == 'readFileMetadata') {
+              return jsonEncode({
+                'title': 'Embedded title',
+                'audio_codec': 'opus',
+              });
+            }
+            fail('Unexpected method: ${call.method}');
+          });
+
+      final result = await PlatformBridge.readDisplayAudioMetadata(
+        'content://downloads/misnamed.flac',
+      );
+
+      expect(invokedMethods, ['readAudioMetadata', 'readFileMetadata']);
+      expect(result['title'], 'Embedded title');
+      expect(result['audio_codec'], 'opus');
+    },
+  );
+}