PlatformOrder create: autofill merchant/plan from subscription defaults

app/Http/Controllers/Admin/PlatformOrderController.php

@@ -56,6 +56,17 @@ class PlatformOrderController extends Controller
             $siteSubscription = SiteSubscription::query()->with(['merchant', 'plan'])->find($siteSubscriptionId);
         }
 
+        // 续费下单场景：若带了 site_subscription_id，但未显式指定 merchant/plan，则从订阅上补齐默认值。
+        // 目的：让“从订阅维度跳转到下单页”的链路更稳，不必每次手工二次选择。
+        if ($siteSubscription) {
+            if ((int) ($defaults['merchant_id'] ?? 0) <= 0) {
+                $defaults['merchant_id'] = (int) ($siteSubscription->merchant_id ?? 0);
+            }
+            if ((int) ($defaults['plan_id'] ?? 0) <= 0) {
+                $defaults['plan_id'] = (int) ($siteSubscription->plan_id ?? 0);
+            }
+        }
+
         return view('admin.platform_orders.form', [
             'merchants' => $merchants,
             'plans' => $plans,