fix: Idempotent cart completion (#9231)

What
- Store result of cart-completion workflow for three days by default
  - This enables the built-in idempotency mechanism to kick-in, provided the same transaction ID is used on workflow executions
- Return order from cart-completion workflow if the cart has already been completed
  - In case transaction ID is not used on workflow executions, we still only want to complete a cart once

packages/medusa/src/subscribers/payment-webhook.ts

@@ -1,8 +1,16 @@
+import {
+  onPaymentProcessedWorkflow,
+  processPaymentWorkflow,
+} from "@medusajs/core-flows"
 import {
   IPaymentModuleService,
   ProviderWebhookPayload,
 } from "@medusajs/framework/types"
-import { Modules, PaymentWebhookEvents } from "@medusajs/framework/utils"
+import {
+  Modules,
+  PaymentActions,
+  PaymentWebhookEvents,
+} from "@medusajs/framework/utils"
 import { SubscriberArgs, SubscriberConfig } from "../types/subscribers"
 
 type SerializedBuffer = {
@@ -27,7 +35,25 @@ export default async function paymentWebhookhandler({
       (input.payload.rawData as unknown as SerializedBuffer).data
     )
   }
-  await paymentService.processEvent(input)
+
+  const processedEvent = await paymentService.getWebhookActionAndData(input)
+
+  if (processedEvent?.action === PaymentActions.NOT_SUPPORTED) {
+    return
+  }
+
+  if (!processedEvent.data) {
+    return
+  }
+
+  await processPaymentWorkflow(container).run({
+    input: processedEvent,
+  })
+
+  // We process the intended side effects of payment processing separately.
+  await onPaymentProcessedWorkflow(container).run({
+    input: processedEvent,
+  })
 }
 
 export const config: SubscriberConfig = {