fix(sync): 数据同步合并化 + 排行榜缓存与游标分页

- storage: 新增 mergeRecords,云端记录与本地按 id 去重合并,restore
  不再覆盖,解决训练中冷启动丢记录与多设备记录丢失
- storage: 新增 recomputeStreak,restore 后基于合并记录重算 streak,
  不再信任云端 streak 值
- storage: 新增 _local_changed_at 标记,settings/profile/customPlans
  在本地有未同步改动时保留本地,避免被云端旧值覆盖
- app: _restoreFromCloud 改合并 + 时间戳保护 + streak 重算;Case 2
  合并后回推让两端收敛
- leaderboard: 模块级 60s 缓存 + 游标分页(_id > lastId)替代 skip,
  全表扫描从每次打开降到 60s 内一次

Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>

utils/storage.js

@@ -9,6 +9,17 @@ const PROFILE_KEY = 'user_profile'
 
 let _idSeq = 0
 
+/**
+ * Record the timestamp of the last local mutation to single-value fields
+ * (settings / profile / customPlans / theme). _restoreFromCloud compares
+ * this against the cloud doc's updatedAt: if local changed after the cloud
+ * snapshot, we keep local to avoid clobbering unsynced edits. Records are
+ * exempt - they go through mergeRecords() which never loses data.
+ */
+const _markLocalChanged = () => {
+  try { wx.setStorageSync('_local_changed_at', Date.now()) } catch (e) {}
+}
+
 /**
  * Backfill an `id` for any record that doesn't have one.
  * Older records (e.g. data restored from cloud or migrated from a build
@@ -90,6 +101,49 @@ const deleteRecord = (recordId) => {
   cloud.pushAll()
 }
 
+/**
+ * Merge cloud records into local records WITHOUT losing either side.
+ *
+ * Why this exists: _restoreFromCloud used to overwrite training_records
+ * with the cloud doc verbatim. If the user finished a training during the
+ * async pullAll on launch, saveRecord had already written locally, and the
+ * subsequent restore wiped that fresh record with the cloud's older
+ * snapshot. Same hazard for multi-device edits.
+ *
+ * Dedup: records with a real (non-legacy) id dedup by id; legacy/idless
+ * records dedup by `date|duration` so old migrated data doesn't double up.
+ * Result is re-bucketed by month and sorted newest-first.
+ */
+const mergeRecords = (cloudRecords) => {
+  const local = wx.getStorageSync(RECORDS_KEY) || {}
+  const cloud = (cloudRecords && typeof cloudRecords === 'object') ? cloudRecords : {}
+  const seen = new Set()
+  const out = []
+  const push = (r) => {
+    if (!r) return
+    const id = r.id
+    const isRealId = id != null && id !== '' && !String(id).startsWith('legacy-')
+    const key = isRealId ? `id:${id}` : `c:${r.date}|${r.duration}`
+    if (seen.has(key)) return
+    seen.add(key)
+    out.push(r)
+  }
+  Object.keys(local).forEach((m) => (local[m] || []).forEach(push))
+  Object.keys(cloud).forEach((m) => (cloud[m] || []).forEach(push))
+
+  const merged = {}
+  out.forEach((r) => {
+    const mo = (r.date && r.date.substring) ? r.date.substring(0, 7) : 'unknown'
+    if (!merged[mo]) merged[mo] = []
+    merged[mo].push(r)
+  })
+  Object.keys(merged).forEach((mo) => {
+    merged[mo].sort((a, b) => (b.date || '').localeCompare(a.date || ''))
+  })
+  _ensureRecordIds(merged)
+  return merged
+}
+
 const getRecordsByMonth = (month) => {
   const records = getRecords()
   return records[month] || []
@@ -118,6 +172,7 @@ const getSettings = () => wx.getStorageSync(SETTINGS_KEY) || {
 
 const saveSettings = (settings) => {
   wx.setStorageSync(SETTINGS_KEY, settings)
+  _markLocalChanged()
   cloud.pushAll()
 }
 
@@ -145,6 +200,7 @@ const saveProfile = (profile) => {
     clean.avatarUrl = profile.avatarUrl
   }
   wx.setStorageSync(PROFILE_KEY, clean)
+  _markLocalChanged()
   cloud.pushAll()
   return clean
 }
@@ -170,6 +226,7 @@ const saveCustomPlan = (planId, planData) => {
   const plans = getCustomPlans()
   plans[planId] = planData
   wx.setStorageSync(CUSTOM_PLANS_KEY, plans)
+  _markLocalChanged()
   cloud.pushAll()
 }
 
@@ -179,6 +236,7 @@ const resetCustomPlan = (planId) => {
   if (!(planId in plans)) return
   delete plans[planId]
   wx.setStorageSync(CUSTOM_PLANS_KEY, plans)
+  _markLocalChanged()
   cloud.pushAll()
 }
 
@@ -252,6 +310,41 @@ const validateStreak = () => {
   return streak
 }
 
+/**
+ * Fully recompute the streak from actual training records. Used after a
+ * cloud restore/merge: the cloud doc's streak may be stale or belong to
+ * another device, so we trust the merged records over the cloud value.
+ */
+const recomputeStreak = () => {
+  const records = getRecords()
+  const allDates = new Set()
+  Object.values(records).forEach((monthRecs) => {
+    monthRecs.forEach((r) => allDates.add(dateOnly(r.date)))
+  })
+  const sorted = Array.from(allDates).sort().reverse()
+  if (sorted.length === 0) {
+    const empty = { count: 0, lastDate: '' }
+    wx.setStorageSync(STREAK_KEY, empty)
+    return empty
+  }
+  let count = 1
+  let prev = sorted[0]
+  for (let i = 1; i < sorted.length; i++) {
+    const prevDate = new Date(prev.replace(/-/g, '/'))
+    const curDate = new Date(sorted[i].replace(/-/g, '/'))
+    const diff = Math.round((prevDate - curDate) / (1000 * 60 * 60 * 24))
+    if (diff === 1) {
+      count++
+      prev = sorted[i]
+    } else {
+      break
+    }
+  }
+  const streak = { count, lastDate: sorted[0] }
+  wx.setStorageSync(STREAK_KEY, streak)
+  return streak
+}
+
 const updateStreak = (date) => {
   const streak = getStreak()
   const todayFull = date || getToday()
@@ -310,6 +403,7 @@ module.exports = {
   getRecords,
   saveRecord,
   deleteRecord,
+  mergeRecords,
   getRecordsByMonth,
   getTotalStats,
   getSettings,
@@ -321,6 +415,7 @@ module.exports = {
   saveProfile,
   getStreak,
   validateStreak,
+  recomputeStreak,
   updateStreak,
   getToday,
   getDateOffset,