Feature: Adding Checkout Services and Events

src/Checkout/Exceptions/InvalidShippingOptionException.php

@@ -0,0 +1,21 @@
+<?php
+
+namespace Modules\Core\Checkout\Exceptions;
+
+use RuntimeException;
+
+/**
+ * Thrown by CheckoutService::selectShippingOption() when the given
+ * identifier doesn't resolve to a real, currently-available ShippingOption
+ * for the cart — Lunar's own ShippingManifest::getOption() just returns
+ * null, it has no matching exception type of its own to reuse here (same
+ * reasoning as Modules\Core\Cart\Exceptions\InvalidCouponException for
+ * Discounts::validateCoupon()).
+ */
+class InvalidShippingOptionException extends RuntimeException
+{
+    public function __construct(public readonly string $identifier)
+    {
+        parent::__construct("The shipping option \"{$identifier}\" is not available for this cart.");
+    }
+}