feat(core-flows,types,utils,medusa): Update existing line items when adding the same variant to cart (#7470)

* feat(core-flows,types,utils,medusa): Update existing line items when adding the same variant to cart

* chore: split steps into 2 for add-to-cart

* chore: split steps into 2 for add-to-cart

* chore: iterate safely

* chore: parallelize upsert

packages/medusa/src/api/store/carts/query-config.ts

@@ -45,6 +45,7 @@ export const defaultStoreCartFields = [
   "items.variant_sku",
   "items.variant_barcode",
   "items.variant_title",
+  "items.metadata",
   "items.created_at",
   "items.updated_at",
   "items.title",

packages/medusa/src/api/store/carts/validators.ts

@@ -8,6 +8,7 @@ export const StoreGetCartsCart = createSelectParams()
 const ItemSchema = z.object({
   variant_id: z.string(),
   quantity: z.number(),
+  metadata: z.record(z.unknown()).optional().nullable(),
 })
 
 export type StoreCreateCartType = z.infer<typeof StoreCreateCart>
@@ -62,7 +63,7 @@ export type StoreAddCartLineItemType = z.infer<typeof StoreAddCartLineItem>
 export const StoreAddCartLineItem = z.object({
   variant_id: z.string(),
   quantity: z.number(),
-  metadata: z.record(z.unknown()).optional(),
+  metadata: z.record(z.unknown()).optional().nullable(),
 })
 
 export type StoreUpdateCartLineItemType = z.infer<