Enhance: plans index show safe back link

resources/views/admin/plans/index.blade.php

@@ -29,6 +29,16 @@
 <div class="card mb-20">
     <p class="muted muted-tight">这里是总台视角的套餐目录页，用于沉淀平台可售卖的标准能力包。</p>
     <p class="muted">当前阶段先完成套餐主数据可见、可筛与口径收拢，后续再接授权项、售价规则与上下架动作。</p>
+
+    @php
+        $incomingBack = (string) request()->query('back', '');
+        $safeBack = str_starts_with($incomingBack, '/') ? $incomingBack : '';
+    @endphp
+    @if($safeBack)
+        <div class="mt-10">
+            <a href="{{ $safeBack }}" class="muted">← 返回上一页（保留上下文）</a>
+        </div>
+    @endif
 </div>
 
 <div class="card mb-20">

tests/Feature/AdminPlanIndexBackLinkTest.php

@@ -0,0 +1,40 @@
+<?php
+
+namespace Tests\Feature;
+
+use Illuminate\Foundation\Testing\RefreshDatabase;
+use Tests\TestCase;
+
+class AdminPlanIndexBackLinkTest 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_index_should_show_safe_back_link_when_back_is_relative_path(): void
+    {
+        $this->loginAsPlatformAdmin();
+
+        $this->get('/admin/plans?status=active&back=' . urlencode('/admin/site-subscriptions?status=activated'))
+            ->assertOk()
+            ->assertSee('返回上一页（保留上下文）')
+            ->assertSee('href="/admin/site-subscriptions?status=activated"', false);
+    }
+
+    public function test_index_should_not_show_back_link_when_back_is_external_url(): void
+    {
+        $this->loginAsPlatformAdmin();
+
+        $this->get('/admin/plans?back=' . urlencode('https://evil.example.com/'))
+            ->assertOk()
+            ->assertDontSee('返回上一页（保留上下文）');
+    }
+}