fix(miniprogram): F1-5b MP-4 coach-detail id 边界保护 (W1)

走查发现 pages/coach-detail 在某种入口下 data.coachId 为 undefined /
空字符串,导致后端 /api/xcx/coaches/undefined 请求 422,体现为助教
详情页加载失败。后端日志多次出现该 422 记录。

变更:
- apps/miniprogram/miniprogram/pages/coach-detail/coach-detail.ts:247
  onLoad 加 guard(参考 coach-service-records.ts 同款模式):
  - 检查 options.id 非空 + 非字面 'undefined'
  - 数字格式校验 (^\d+$)
  - 失败时 wx.showToast("缺少助教标识") + 1s 后 navigateBack
    (失败时 fallback switchTab board-finance)

双口径验证(weixin-devtools-mcp):
- 缺参入口 /pages/coach-detail/coach-detail(无 query) → guard 触发,
  toast 显示 + 退回 board-finance,不再发出 422 请求
- 正常入口 ?id=3148987180059141 → 通过 guard,pageState=normal 加载成功

§3.3 标"sandbox 无关",4b 跳过(权限/参数路径与 sandbox 无关联)。

审计:docs/audit/changes/2026-05-05__wave1_f1_5b_mp4_coach_detail_id_guard.md

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

apps/miniprogram/miniprogram/pages/coach-detail/coach-detail.ts

@@ -244,10 +244,22 @@ Page({
   _longPressed: false,
   _animTimer: null as ReturnType<typeof setTimeout> | null,
 
+  // CHANGE 2026-05-05 | F1-5b MP-4: 补 id 边界保护,
+  // 防止 options.id 缺失或为字符串 'undefined' 时调用 /api/xcx/coaches/undefined 触发 422
   onLoad(options: { id?: string }) {
-    const id = options?.id || ''
-    this.setData({ coachId: id })
-    this.loadData(id)
+    const raw = options?.id
+    const idStr = (raw && raw !== 'undefined') ? String(raw) : ''
+    if (!idStr || !/^\d+$/.test(idStr)) {
+      wx.showToast({ title: '缺少助教标识', icon: 'none' })
+      setTimeout(() => {
+        wx.navigateBack({
+          fail: () => wx.switchTab({ url: '/pages/board-finance/board-finance' }),
+        })
+      }, 1000)
+      return
+    }
+    this.setData({ coachId: idStr })
+    this.loadData(idStr)
   },
 
   onHide() {