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

app/Domains/Purchase/Requests/UpdatePurchaseItemRequest.php

@@ -0,0 +1,22 @@
+<?php
+
+namespace App\Domains\Purchase\Requests;
+
+use Illuminate\Foundation\Http\FormRequest;
+
+class UpdatePurchaseItemRequest extends FormRequest
+{
+    public function authorize(): bool
+    {
+        return $this->user() !== null;
+    }
+
+    /** @return array<string, mixed> */
+    public function rules(): array
+    {
+        return [
+            'quantity' => ['sometimes', 'required_without:variant_id', 'integer', 'min:1', 'max:100'],
+            'variant_id' => ['sometimes', 'required_without:quantity', 'integer', 'min:1'],
+        ];
+    }
+}