修复2个小程序Bug：库存上限检查+同城配送费归零 + 修复空购物车蓝本选择器

Author: zcj220

miniprogram-demo/pages/checkout/checkout.js

@@ -56,11 +56,10 @@ Page({
     const type = types[e.detail.value];
     getApp().globalData.deliveryType = type;
 
-    // BUG 4（隐蔽）: 同城配送应该免费(0元)，但实际收了5元
-    // express 收 10元
+    // BUG 4 已修复: 同城配送免费(0元)
     let fee = 0;
     if (type === 'same_city') {
-      fee = 5;   // 应该是 0，这是Bug
+      fee = 0;
     } else if (type === 'express') {
       fee = 10;
     }

miniprogram-demo/pages/index/index.js

@@ -77,8 +77,12 @@ Page({
       return;
     }
 
-    // BUG 2（隐蔽）: 库存检查只看是否>0，不检查购物车中已有数量
-    // 库存10但可以无限加入购物车
+    // BUG 2 已修复: 检查购物车中已有数量是否超过库存
+    const cartQty = app.globalData.cart.filter(c => c.id === product.id).length;
+    if (cartQty >= product.stock) {
+      this.setData({ message: product.name + ' 已达库存上限(' + product.stock + ')', msgClass: 'err' });
+      return;
+    }
 
     // 计算价格
     let price = product.price;

miniprogram-demo/testpilot/testpilot.json

@@ -121,14 +121,13 @@
         },
         {
           "name": "场景10：空购物车结算验证",
-          "description": "购物车为空时不应允许结算",
+          "description": "购物车为空时不应显示结算按钮，应显示空购物车提示",
           "steps": [
             {"action": "reset_state", "description": "重置状态回首页"},
             {"action": "navigate_to", "value": "/pages/cart/cart", "description": "直接跳到空购物车"},
-            {"action": "read_text", "target": ".empty-cart", "description": "读取空购物车提示"},
-            {"action": "click", "target": ".btn-checkout", "description": "尝试点结算按钮"},
-            {"action": "wait", "value": "500", "description": "等待"},
-            {"action": "evaluate", "value": "getCurrentPages()[getCurrentPages().length-1].route", "expected": "cart", "description": "验证仍在购物车页（未跳到结算页）"},
+            {"action": "read_text", "target": ".empty-text", "expected": "空", "description": "验证显示空购物车提示"},
+            {"action": "page_query", "target": ".btn-checkout", "value": "count", "expected": "0", "description": "验证结算按钮不存在（空购物车不应有结算入口）"},
+            {"action": "read_text", "target": ".btn-back", "expected": "去购物", "description": "验证显示去购物按钮"},
             {"action": "screenshot", "description": "截图：空购物车"}
           ]
         }