feat(cart): enhance item update functionality to support variant changes and improve cart editing policies

app/Domains/Purchase/Models/PurchaseItem.php

@@ -3,6 +3,8 @@
 namespace App\Domains\Purchase\Models;
 
 use App\Domains\Attachable\Models\Attachment;
+use App\Domains\Catalog\Models\CatalogItem;
+use App\Domains\Catalog\Models\Variant;
 use Illuminate\Database\Eloquent\Attributes\Fillable;
 use Illuminate\Database\Eloquent\Factories\HasFactory;
 use Illuminate\Database\Eloquent\Model;
@@ -66,4 +68,16 @@ class PurchaseItem extends Model
     {
         return $this->belongsTo(Attachment::class, 'image_attachment_id');
     }
+
+    /** @return BelongsTo<CatalogItem, $this> */
+    public function sourceCatalogItem(): BelongsTo
+    {
+        return $this->belongsTo(CatalogItem::class, 'source_catalog_item_id')->withTrashed();
+    }
+
+    /** @return BelongsTo<Variant, $this> */
+    public function sourceVariant(): BelongsTo
+    {
+        return $this->belongsTo(Variant::class, 'source_variant_id')->withTrashed();
+    }
 }