fix(extensions): preserve verification callback retries

lib/utils/extension_session_callback.dart

@@ -0,0 +1,75 @@
+typedef ExtensionSessionGrantCallback = ({String grant, String state});
+
+ExtensionSessionGrantCallback? parseExtensionSessionGrantCallback(String text) {
+  final trimmed = text.trim();
+  if (trimmed.isEmpty) return null;
+
+  String? grant;
+  String? state;
+  final uri = Uri.tryParse(trimmed);
+  if (uri != null) {
+    grant = _nonEmpty(
+      uri.queryParameters['grant'] ?? uri.queryParameters['code'],
+    );
+    state = _nonEmpty(uri.queryParameters['state']);
+
+    final nestedCallback = _nonEmpty(uri.queryParameters['cb']);
+    if (grant == null && nestedCallback != null) {
+      final nested = parseExtensionSessionGrantCallback(nestedCallback);
+      if (nested != null) return nested;
+    }
+  }
+
+  grant ??= _decodedRegexGroup(
+    trimmed,
+    RegExp(r'(?:^|[?&#\s])grant=([^&#\s]+)'),
+  );
+  grant ??= _decodedRegexGroup(
+    trimmed,
+    RegExp(r'(?:^|[?&#\s])code=([^&#\s]+)'),
+  );
+  state ??= _decodedRegexGroup(
+    trimmed,
+    RegExp(r'(?:^|[?&#\s])state=([^&#\s]+)'),
+  );
+
+  grant = _nonEmpty(grant);
+  state = _nonEmpty(state);
+  if (grant == null || state == null) return null;
+  return (grant: grant, state: state);
+}
+
+String? extensionCallbackStateFromVerificationUri(Uri uri, [int depth = 0]) {
+  if (depth > 3) return null;
+
+  final directState = _nonEmpty(uri.queryParameters['state']);
+  if (directState != null) return directState;
+
+  for (final key in const ['cb', 'callback', 'callback_url', 'redirect_uri']) {
+    final nestedText = _nonEmpty(uri.queryParameters[key]);
+    if (nestedText == null) continue;
+    final nestedUri = Uri.tryParse(nestedText);
+    if (nestedUri == null) continue;
+    final nestedState = extensionCallbackStateFromVerificationUri(
+      nestedUri,
+      depth + 1,
+    );
+    if (nestedState != null) return nestedState;
+  }
+  return null;
+}
+
+String? _decodedRegexGroup(String input, RegExp regex) {
+  final value = _nonEmpty(regex.firstMatch(input)?.group(1));
+  if (value == null) return null;
+  try {
+    return Uri.decodeComponent(value);
+  } on FormatException {
+    return null;
+  }
+}
+
+String? _nonEmpty(String? value) {
+  final trimmed = value?.trim() ?? '';
+  return trimmed.isEmpty ? null : trimmed;
+}