fix(backurl): avoid duplicating back query when already present

tests/Unit/BackUrlWithBackNoDuplicateTest.php

@@ -0,0 +1,27 @@
+<?php
+
+namespace Tests\Unit;
+
+use App\Support\BackUrl;
+use Illuminate\Support\Arr;
+use Tests\TestCase;
+
+class BackUrlWithBackNoDuplicateTest extends TestCase
+{
+    public function test_with_back_should_not_duplicate_when_path_already_has_back_query(): void
+    {
+        $back = '/admin/platform-orders/2';
+
+        $path = '/admin/site-subscriptions/2?' . Arr::query([
+            'back' => $back,
+            'order_sync_status' => 'syncable',
+        ]);
+
+        $url = BackUrl::withBack($path, $back);
+
+        $this->assertSame($path, $url);
+
+        // 防止重复 back= 出现两次
+        $this->assertSame(1, substr_count($url, 'back='));
+    }
+}