fixup! TF-4224 Reduce ReDoS vulnerability

core/lib/utils/string_convert.dart

@@ -4,6 +4,7 @@ import 'dart:typed_data';
 import 'package:core/utils/app_logger.dart';
 import 'package:core/domain/exceptions/string_exception.dart';
 import 'package:core/utils/mail/named_address.dart';
+import 'package:flutter/widgets.dart' show visibleForTesting;
 import 'package:html/dom.dart';
 import 'package:html/parser.dart';
 import 'package:http_parser/http_parser.dart';
@@ -21,6 +22,9 @@ class StringConvert {
   static final _asciiArtRegex = RegExp(r'[+\-|/\\=]');
   static final _namedAddressRegex = RegExp(r'''(?:(?:"([^"]+)"|'([^']+)')\s*)?<([^>]+)>''');
 
+  @visibleForTesting
+  static RegExp get base64ValidationRegex => _base64ValidationRegex;
+
   static String? writeEmptyToNull(String text) {
     if (text.isEmpty) return null;
     return text;

core/test/utils/redos_vulnerability_test.dart

@@ -361,23 +361,9 @@ void main() {
     group('Regex initialization optimization', () {
       test('regex patterns should be reused, not recreated', () {
         // This test verifies that regex patterns are static and reused
-        // We can't directly test if they're the same object, but we can
-        // verify performance doesn't degrade with multiple calls
-
-        const iterations = 1000;
-        final stopwatch = Stopwatch()..start();
-
-        for (var i = 0; i < iterations; i++) {
-          StringConvert.isTextTable('| a | b |\n|---|---|\n| c | d |');
-          HtmlUtils.wrapPlainTextLinks('<p>https://example.com</p>');
-          StringConvert.extractEmailAddress('test@example.com, test2@example.com');
-        }
-
-        stopwatch.stop();
-
-        // If regex patterns were being recreated each time, this would be much slower
-        expect(stopwatch.elapsedMilliseconds, lessThan(500),
-            reason: 'Multiple calls should be fast due to regex reuse');
+        final regex1 = StringConvert.base64ValidationRegex;
+        final regex2 = StringConvert.base64ValidationRegex;
+        expect(identical(regex1, regex2), true);
       });
     });
   });