Enhance: platform order create flow carries back and redirects with back

tests/Feature/AdminPlatformOrderCreateBackFlowTest.php

@@ -0,0 +1,73 @@
+<?php
+
+namespace Tests\Feature;
+
+use App\Models\Merchant;
+use App\Models\Plan;
+use Illuminate\Foundation\Testing\RefreshDatabase;
+use Tests\TestCase;
+
+class AdminPlatformOrderCreateBackFlowTest extends TestCase
+{
+    use RefreshDatabase;
+
+    protected function loginAsPlatformAdmin(): void
+    {
+        $this->seed();
+
+        $this->post('/admin/login', [
+            'email' => 'platform.admin@demo.local',
+            'password' => 'Platform@123456',
+        ])->assertRedirect('/admin');
+    }
+
+    public function test_create_form_renders_safe_back_button_when_back_present(): void
+    {
+        $this->loginAsPlatformAdmin();
+
+        $back = '/admin/site-subscriptions/1';
+
+        $this->get('/admin/platform-orders/create?back=' . urlencode($back))
+            ->assertOk()
+            ->assertSee('返回（保留上下文）')
+            ->assertSee('href="' . $back . '"', false)
+            ->assertSee('name="back"', false);
+    }
+
+    public function test_store_redirects_to_show_with_back_when_back_is_safe_relative_path(): void
+    {
+        $this->loginAsPlatformAdmin();
+
+        $merchant = Merchant::query()->firstOrFail();
+        $plan = Plan::query()->create([
+            'code' => 'po_create_back_flow_plan',
+            'name' => '创建订单 back 流程测试套餐',
+            'billing_cycle' => 'monthly',
+            'price' => 10,
+            'list_price' => 10,
+            'status' => 'active',
+            'sort' => 10,
+            'published_at' => now(),
+        ]);
+
+        $back = '/admin/site-subscriptions/123?status=activated';
+
+        $res = $this->post('/admin/platform-orders', [
+            'merchant_id' => $merchant->id,
+            'plan_id' => $plan->id,
+            'order_type' => 'new_purchase',
+            'quantity' => 1,
+            'discount_amount' => 0,
+            'payment_channel' => 'offline',
+            'remark' => 'back flow',
+            'back' => $back,
+        ]);
+
+        $res->assertRedirect();
+        $location = $res->headers->get('Location');
+
+        $this->assertNotNull($location);
+        $this->assertStringContainsString('/admin/platform-orders/', $location);
+        $this->assertStringContainsString('back=' . urlencode($back), $location);
+    }
+}