fix(checkout): take a repeated capture as a successful payment

The CMS answers a capture of an order already paid with this PayPal order
with { success: true, alreadyCaptured: true } instead of the order. Step 3
took that answer for a capture without authorisation and showed a payment
error. It now reloads the paid order (keeping the shown one if the reload
fails) and continues as after a first capture: confirmation, the
checkout-payment-completed event, and the redirect to the order's result
page. capturePayment is typed as Order | AlreadyCaptured, and the pure
isAlreadyCaptured (utils/captureResponse.ts) tells them apart.

Refs libretech/mp#71

pages/checkout/3.vue

@@ -191,6 +191,7 @@
 import { numberFormatter } from "~/utils/numberFormatter";
 import { trackEvent } from "~/utils/trackEvent";
 import { checkoutErrorMessageFor } from "~/utils/checkoutError";
+import { isAlreadyCaptured } from "~/utils/captureResponse";
 import type { Order } from "~/types";
 
 const config = useRuntimeConfig();
@@ -312,10 +313,14 @@ async function initializePayPalButtons() {
 				onApprove: async (data) => {
 					try {
 						// Capture payment server-side (CMS captures via PayPal server SDK and updates order)
-						const capturedOrder = await shopApi.capturePayment(orderData.value.uuid, data.orderID!);
+						const captured = await shopApi.capturePayment(orderData.value.uuid, data.orderID!);
 
-						if (capturedOrder.paymentAuthorised) {
-							orderData.value = capturedOrder;
+						if (isAlreadyCaptured(captured)) {
+							// An earlier capture of this PayPal order went through: reload the paid order, keeping the shown one if that fails.
+							orderData.value = await shopApi.getOrder(orderData.value.uuid).catch(() => orderData.value);
+							await handleSuccessfulPayment();
+						} else if (captured.paymentAuthorised) {
+							orderData.value = captured;
 							await handleSuccessfulPayment();
 						} else {
 							console.error("Payment capture did not result in authorisation");