add_filter('woocommerce_add_to_cart_validation', function($ok, $pid, $qty){
  if (strtoupper($_SERVER['REQUEST_METHOD'] ?? '') !== 'POST') return false;
  if (empty($_POST['_wpnonce']) || !wp_verify_nonce($_POST['_wpnonce'], 'woocommerce-cart')) return false;
  return $ok;
}, 10, 3);