fix(backup): close archive outputs when extraction fails

lib/services/backup_service.dart

@@ -3,6 +3,7 @@ import 'dart:io';
 import 'dart:isolate';
 
 import 'package:archive/archive_io.dart';
+import 'package:flutter/foundation.dart';
 import 'package:path/path.dart' as p;
 import 'package:path_provider/path_provider.dart';
 import 'package:spotiflac_android/constants/app_info.dart';
@@ -371,9 +372,7 @@ class BackupService {
       String? historyPath;
       if (historyEntry != null) {
         historyPath = p.join(extractionDir.path, 'history.ndjson');
-        final historyOutput = OutputFileStream(historyPath);
-        historyEntry.writeContent(historyOutput);
-        historyOutput.closeSync();
+        writeArchiveEntry(historyEntry, OutputFileStream(historyPath));
       }
 
       final restoredCovers = <String, dynamic>{};
@@ -399,9 +398,7 @@ class BackupService {
           var ext = cover['ext']?.toString() ?? '.jpg';
           if (!RegExp(r'^\.[a-z0-9]{1,8}$').hasMatch(ext)) ext = '.jpg';
           final coverPath = p.join(extractionDir.path, 'cover_${index++}$ext');
-          final output = OutputFileStream(coverPath);
-          archiveEntry.writeContent(output);
-          output.closeSync();
+          writeArchiveEntry(archiveEntry, OutputFileStream(coverPath));
           extractedCoverBytes += archiveEntry.size;
           restoredCovers[manifestEntry.key.toString()] = {
             'ext': ext,
@@ -428,12 +425,7 @@ class BackupService {
             throw const FormatException('Missing or oversized profile photo');
           }
           photoPath = p.join(extractionDir.path, 'profile.png');
-          final output = OutputFileStream(photoPath);
-          try {
-            photoEntry.writeContent(output);
-          } finally {
-            output.closeSync();
-          }
+          writeArchiveEntry(photoEntry, OutputFileStream(photoPath));
         }
         profile = UserProfile(
           name: rawProfile['name'] as String,
@@ -469,6 +461,16 @@ class BackupService {
     }
   }
 
+  /// Consumes and closes the output even when an archive payload cannot be read.
+  @visibleForTesting
+  static void writeArchiveEntry(ArchiveFile entry, OutputFileStream output) {
+    try {
+      entry.writeContent(output);
+    } finally {
+      output.closeSync();
+    }
+  }
+
   static BackupBundle? parse(String content) {
     dynamic decoded;
     try {

test/backup_service_v2_test.dart

@@ -6,7 +6,38 @@ import 'package:flutter_test/flutter_test.dart';
 import 'package:path/path.dart' as p;
 import 'package:spotiflac_android/services/backup_service.dart';
 
+class _UnreadableArchiveFile extends ArchiveFile {
+  _UnreadableArchiveFile(this.failure) : super('history.ndjson', 0, <int>[]);
+
+  final FormatException failure;
+
+  @override
+  void writeContent(OutputStream output, {bool freeMemory = true}) {
+    output.writeBytes([1, 2, 3]);
+    throw failure;
+  }
+}
+
 void main() {
+  test('archive output closes when reading its payload throws', () async {
+    final root = await Directory.systemTemp.createTemp('unreadable-backup-');
+    addTearDown(() => root.delete(recursive: true));
+    final path = p.join(root.path, 'history.ndjson');
+    final output = OutputFileStream(path);
+    const failure = FormatException('Invalid compressed archive payload');
+
+    expect(
+      () => BackupService.writeArchiveEntry(
+        _UnreadableArchiveFile(failure),
+        output,
+      ),
+      throwsA(same(failure)),
+    );
+
+    expect(output.isOpen, isFalse);
+    expect(await File(path).readAsBytes(), [1, 2, 3]);
+  });
+
   test(
     'ZIP backup pages history and streams cover files during restore',
     () async {