On-site checkout broken on Commerce 3.3+ — Onsite::create() bypasses the checkout-add-payment-method BC shim

Problem/Motivation

On Drupal Commerce 3.3.0+, the on-site gateway can no longer collect a card during checkout. The card form never renders, no payment method is created, and submitting the order fails on the payment step with:

commerce_payment: Unable process payment with eway_gate_onsite

No exception is logged, which makes it look like a misconfiguration rather than a code issue.

Commerce 3.3.0 reworked the payment form (see the Commerce 3.3.0 release notes). The PaymentInformation checkout pane now renders the add-card form only when the gateway has a form registered for the checkout-add-payment-method operation:

// commerce_payment/src/Plugin/Commerce/CheckoutPane/PaymentInformation.php
if ($payment_gateway_plugin instanceof SupportsCreatingPaymentMethodsInterface &&
    $payment_gateway_plugin->hasFormClass('checkout-add-payment-method')) {
  $pane_form = $this->buildPaymentMethodForm($pane_form, $form_state, $default_option);
}

Core provides backward compatibility in PaymentGatewayBase::create(), which copies a gateway's existing add-payment-method form to checkout-add-payment-method:

// commerce_payment/src/Plugin/Commerce/PaymentGateway/PaymentGatewayBase.php
if (isset($instance->pluginDefinition['forms']['add-payment-method']) &&
    !isset($instance->pluginDefinition['forms']['checkout-add-payment-method'])) {
  $instance->pluginDefinition['forms']['checkout-add-payment-method'] = $instance->pluginDefinition['forms']['add-payment-method'];
}

Onsite::create() overrides the parent and builds the instance with new static(...) without ever calling parent::create(), so this shim never runs. As a result hasFormClass('checkout-add-payment-method') returns FALSE and the pane renders nothing.

Steps to reproduce

1. Drupal 10.3+ / Commerce 3.3.0+, eway_commerce2 3.0.0, gateway in on-site mode.
2. Add a product to the cart and proceed to checkout.
3. Observe that no credit-card fields appear in the Payment information pane.
4. Place the order → checkout fails; watchdog logs Unable process payment with eway_gate_onsite.

Confirmed via:

$plugin->hasFormClass('add-payment-method');           // TRUE
$plugin->hasFormClass('checkout-add-payment-method');  // FALSE  ← should be TRUE

Proposed resolution

Declare the checkout-add-payment-method form explicitly on the gateway plugin annotation (simplest, independent of create()):

  *   forms = {
  *     "add-payment-method" = "Drupal\eway_gate\PluginForm\Onsite\PaymentMethodAddForm",
+ *     "checkout-add-payment-method" = "Drupal\eway_gate\PluginForm\Onsite\PaymentMethodAddForm",
  *     "edit-payment-method" = "Drupal\commerce_payment\PluginForm\PaymentMethodEditForm",
  *   },

Alternatively (better long-term), refactor Onsite::create() to call parent::create() and then inject the transaction manager, so it inherits the core BC shim and any future create() behavior instead of re-implementing it.

Remaining tasks

• Decide between the annotation fix and the create() refactor.
• Same review for any other gateway form operations the overridden create() may shadow.
• Reviewed-and-tested.