fix: 修复排行榜数据自增长（冷启动重复创建云端文档）

每次小程序冷启动都会为同一用户创建新的云端文档，
导致 leaderboard 把同一份数据累加 N 次。

改动：
- app.js: onLaunch 改为 async，每次启动先 pullAll 填充 _openid / _docId 缓存
- utils/cloud.js: 引入 _ensureOpenid() 单次解析；_doPush 总是先按 openid
  定位现有文档；update 失败不再回退到 add()（避免创建重复文档）
- utils/storage.js: getTodayRecord 按日期部分比较，修复一天第二次训练

cloudfunctions/leaderboard/index.js

@@ -38,47 +38,38 @@ exports.main = async (event) => {
   const userMap = new Map()
   let skip = 0
 
+  // Defense-in-depth: if a user somehow ends up with multiple docs in the
+  // collection (e.g. before the client-side fix to _doPush landed, or via
+  // a buggy data migration), only the doc with the latest `updatedAt`
+  // counts for each openid. Otherwise we'd sum the same records N times
+  // and inflate the board.
+  //
+  // Why "latest updatedAt" instead of "first one we see": paginated reads
+  // come back in `_id` ascending order, so "first one" is the OLDEST doc.
+  // Records content is identical across duplicates (both came from the
+  // same local state), so duration/sessions are unaffected — but the
+  // oldest doc carries the OLDEST profile.nickname. Picking the latest
+  // doc gives the freshest nickname even before admin-dedupe runs.
+  const tsOf = (d) => {
+    if (!d.updatedAt) return 0
+    // CloudBase returns Date objects in the SDK, but be defensive in case
+    // a stringified ISO timestamp sneaks through (older SDKs / migrations).
+    if (d.updatedAt instanceof Date) return d.updatedAt.getTime()
+    const t = new Date(d.updatedAt).getTime()
+    return Number.isFinite(t) ? t : 0
+  }
+
+  const latestByOpenid = new Map()
+
   while (true) {
     const res = await db.collection(COLLECTION).skip(skip).limit(PAGE_SIZE).get()
     if (!res.data || res.data.length === 0) break
 
     for (const doc of res.data) {
-      const records = doc.records || {}
-      let duration = 0
-      let sessions = 0
-
-      for (const monthKey of Object.keys(records)) {
-        if (prefix && !monthKey.startsWith(prefix)) continue
-        for (const r of records[monthKey]) {
-          if (period === 'day') {
-            // Use startsWith rather than === to tolerate date strings with
-            // trailing time/zone info (e.g. "2026-06-11T09:11:24.587Z" if
-            // some legacy path stored an ISO date) and to be timezone-
-            // agnostic when client local date differs from server UTC date.
-            if (r.date.startsWith(exact)) { duration += r.duration; sessions++ }
-          } else {
-            if (r.date.startsWith(prefix)) { duration += r.duration; sessions++ }
-          }
-        }
-      }
-
-      if (duration > 0) {
-        const openid = doc._openid || 'unknown'
-        const entry = userMap.get(openid)
-        const profile = doc.profile || {}
-        if (entry) {
-          entry.duration += duration
-          entry.sessions += sessions
-          // Refresh nickname in case the user updated it since last write
-          if (profile.nickname) entry.nickname = profile.nickname
-        } else {
-          userMap.set(openid, {
-            openid,
-            duration,
-            sessions,
-            nickname: profile.nickname || ''
-          })
-        }
+      const openid = doc._openid || 'unknown'
+      const current = latestByOpenid.get(openid)
+      if (!current || tsOf(doc) > tsOf(current)) {
+        latestByOpenid.set(openid, doc)
       }
     }
 
@@ -86,6 +77,40 @@ exports.main = async (event) => {
     skip += PAGE_SIZE
   }
 
+  // Second pass: each openid appears exactly once, so the accumulation
+  // logic doesn't need any dedup guards.
+  for (const doc of latestByOpenid.values()) {
+    const openid = doc._openid || 'unknown'
+    const records = doc.records || {}
+    let duration = 0
+    let sessions = 0
+
+    for (const monthKey of Object.keys(records)) {
+      if (prefix && !monthKey.startsWith(prefix)) continue
+      for (const r of records[monthKey]) {
+        if (period === 'day') {
+          // Use startsWith rather than === to tolerate date strings with
+          // trailing time/zone info (e.g. "2026-06-11T09:11:24.587Z" if
+          // some legacy path stored an ISO date) and to be timezone-
+          // agnostic when client local date differs from server UTC date.
+          if (r.date.startsWith(exact)) { duration += r.duration; sessions++ }
+        } else {
+          if (r.date.startsWith(prefix)) { duration += r.duration; sessions++ }
+        }
+      }
+    }
+
+    if (duration > 0) {
+      const profile = doc.profile || {}
+      userMap.set(openid, {
+        openid,
+        duration,
+        sessions,
+        nickname: profile.nickname || ''
+      })
+    }
+  }
+
   // Full sorted list (for ranking)
   const allSorted = Array.from(userMap.values())
     .sort((a, b) => b.duration - a.duration)