feat(checkout): track current cart purchase

app/Domains/Cart/Models/Cart.php

@@ -27,6 +27,7 @@ use Symfony\Component\HttpKernel\Exception\NotFoundHttpException;
     'guest_token',
     'status',
     'origin',
+    'current_purchase_id',
 ])]
 class Cart extends Model
 {
@@ -43,6 +44,7 @@ class Cart extends Model
     {
         return [
             'user_id' => 'integer',
+            'current_purchase_id' => 'integer',
         ];
     }
 
@@ -76,6 +78,12 @@ class Cart extends Model
         return $this->hasMany(Purchase::class, 'cart_id');
     }
 
+    /** @return BelongsTo<Purchase, $this> */
+    public function currentPurchase(): BelongsTo
+    {
+        return $this->belongsTo(Purchase::class, 'current_purchase_id');
+    }
+
     public function getTotalAmount(): float
     {
         $items = $this->relationLoaded('items')