Fix data loss bug in header_remover during in-place removal

core/lib/src/header_remover.dart

@@ -206,18 +206,52 @@ String removeHeader(String filepath, {String? outputDir, bool backup = true}) {
 
   final hdrSize = info['header_size'] as int;
 
-  final inRaf = file.openSync(mode: FileMode.read);
-  inRaf.setPositionSync(hdrSize);
-
-  final outSink = File(cleanPath).openSync(mode: FileMode.write);
-  const chunkSize = 1024 * 1024;
-  while (true) {
-    final chunk = inRaf.readSync(chunkSize);
-    if (chunk.isEmpty) break;
-    outSink.writeFromSync(chunk);
+  final tempPath = '$cleanPath.tmp';
+  final tempFile = File(tempPath);
+
+  RandomAccessFile? inRaf;
+  RandomAccessFile? outSink;
+
+  try {
+    inRaf = file.openSync(mode: FileMode.read);
+    inRaf.setPositionSync(hdrSize);
+
+    outSink = tempFile.openSync(mode: FileMode.write);
+    const chunkSize = 1024 * 1024;
+    while (true) {
+      final chunk = inRaf.readSync(chunkSize);
+      if (chunk.isEmpty) break;
+      outSink.writeFromSync(chunk);
+    }
+
+    inRaf.closeSync();
+    inRaf = null;
+
+    outSink.closeSync();
+    outSink = null;
+
+    try {
+      tempFile.renameSync(cleanPath);
+    } catch (_) {
+      tempFile.copySync(cleanPath);
+      if (tempFile.existsSync()) {
+        tempFile.deleteSync();
+      }
+    }
+  } catch (e) {
+    try {
+      inRaf?.closeSync();
+    } catch (_) {}
+    try {
+      outSink?.closeSync();
+    } catch (_) {}
+    if (tempFile.existsSync()) {
+      try {
+        tempFile.deleteSync();
+      } catch (_) {}
+    }
+    rethrow;
   }
-  inRaf.closeSync();
-  outSink.closeSync();
 
   return cleanPath;
 }

core/test/header_remover_test.dart

@@ -45,4 +45,50 @@ void main() {
       tmpDir.deleteSync(recursive: true);
     }
   });
+
+  test('nes_in_place_header_removal_without_backup', () {
+    final tmpDir = Directory.systemTemp.createTempSync('hdr_inplace_test_');
+    try {
+      final romPath = p.join(tmpDir.path, 'game_inplace.nes');
+      final header = [
+        0x4E,
+        0x45,
+        0x53,
+        0x1A,
+        0,
+        0,
+        0,
+        0,
+        0,
+        0,
+        0,
+        0,
+        0,
+        0,
+        0,
+        0,
+      ];
+      final body = List<int>.generate(200, (i) => (i + 1) % 256);
+      File(romPath).writeAsBytesSync([...header, ...body]);
+
+      // Remove header in-place with backup: false (outputDir: null)
+      final cleanPath = removeHeader(romPath, outputDir: null, backup: false);
+      expect(cleanPath, equals(romPath));
+
+      final cleanFile = File(cleanPath);
+      expect(cleanFile.existsSync(), isTrue);
+
+      final cleanBytes = cleanFile.readAsBytesSync();
+      expect(cleanBytes.length, equals(200));
+      expect(cleanBytes.length, greaterThan(0));
+      expect(cleanBytes, equals(body));
+
+      // Ensure no backup file was created
+      expect(File('$romPath.bak').existsSync(), isFalse);
+      // Ensure no temp file remained
+      expect(File('$romPath.tmp').existsSync(), isFalse);
+    } finally {
+      tmpDir.deleteSync(recursive: true);
+    }
+  });
 }