fix(medusa): cart now returns 404 when not found (#13622)

FIXES #10218 
FIXES CORE-739

integration-tests/http/__tests__/cart/store/cart.spec.ts

@@ -9,11 +9,7 @@ import {
   PromotionStatus,
   PromotionType,
 } from "@medusajs/utils"
-import {
-  createAdminUser,
-  generatePublishableKey,
-  generateStoreHeaders,
-} from "../../../../helpers/create-admin-user"
+import { createAdminUser, generatePublishableKey, generateStoreHeaders, } from "../../../../helpers/create-admin-user"
 import { setupTaxStructure } from "../../../../modules/__tests__/fixtures"
 import { createAuthenticatedCustomer } from "../../../../modules/helpers/create-authenticated-customer"
 import { medusaTshirtProduct } from "../../../__fixtures__/product"
@@ -152,6 +148,17 @@ medusaIntegrationTestRunner({
         ).data.promotion
       })
 
+      describe("GET /store/carts/[id]", () => {
+        it("should return 404 when trying to fetch a cart that does not exist", async () => {
+          const response = await api.get(
+            `/store/carts/fake`,
+            storeHeadersWithCustomer
+          ).catch((e) => e)
+
+          expect(response.response.status).toEqual(404)
+        })
+      })
+
       describe("POST /store/carts", () => {
         it("should successfully create a cart", async () => {
           const response = await api.post(