export function extractErrorMessage(err: unknown, fallback = '操作失败'): string {
  if (err && typeof err === 'object' && 'response' in err) {
    const resp = (err as { response?: { data?: { message?: string } } }).response;
    if (resp?.data?.message) return resp.data.message;
  }
  if (err instanceof Error) return err.message;
  return fallback;
}