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  miniprogram/pages/read 阅读页 - 当前处理流程 (ASCII)
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---------- 1. 进入页面 onLoad(options) 总览 ----------

  +------------------+
  | onLoad(options)  |
  +--------+---------+
           |
           v
  +----------------------------------------+
  | sceneStr = options.scene || ''        |
  | parsed = parseScene(sceneStr)         |  <-- utils/scene.js
  | mid = options.mid || parsed.mid ||    |
  |       app.globalData.initialSectionMid|
  | id  = options.id  || parsed.id  ||    |
  |       app.globalData.initialSectionId |
  | ref = options.ref || parsed.ref       |
  +--------+-------------------------------+
           |
           v
  +----------------------------------------+
  | 清除 app.globalData.initialSection*   |
  +--------+-------------------------------+
           |
           v
       [ mid || id ? ]
           |
     No ---+---> 提示「章节参数缺失」, return
           |
     Yes   v
  +----------------------------------------+
  | setData: sectionMid, loading=true      |
  | if (ref): 存 referral_code,            |
  |           app.handleReferralCode(ref)  |
  +--------+-------------------------------+
           |
           v
  +----------------------------------------+
  | Promise.all:                            |
  |   - accessManager.fetchLatestConfig()   |
  |   - /api/.../purchase-status (若登录)  |
  +--------+-------------------------------+
           |
           v
  +----------------------------------------+
  | 计算价格/推荐折扣, setData 配置         |
  +--------+-------------------------------+
           |
           v
  +----------------------------------------+
  | resolvedId = id                        |
  | if (mid && !id):                       |
  |   GET /book/chapter/by-mid/:mid        |
  |   resolvedId = chRes.id                |
  |   prefetchedChapter = chRes            |
  | setData(sectionId: resolvedId)         |
  +--------+-------------------------------+
           |
           v
  +----------------------------------------+
  | accessManager.determineAccessState()   |
  | setData: accessState, canAccess,       |
  |          showPaywall, isLoggedIn       |
  +--------+-------------------------------+
           |
           v
  +----------------------------------------+
  | await loadContent(mid, resolvedId,     |
  |                   accessState,         |
  |                   prefetchedChapter)   |
  +--------+-------------------------------+
           |
           v
  +----------------------------------------+
  | if (canAccess): readingTracker.init() |
  | loadNavigation(resolvedId)            |
  | setData(loading: false)               |
  +----------------------------------------+


---------- 2. scene 闭环（海报生成 <-> 扫码解析）----------

  [ 生成海报 ]
       |
       v
  +----------------------------------------+
  | buildScene({ mid?, id?, ref? })        |  utils/scene.js
  | 例: mid=1, ref=ogpTW5fmXR               |
  |  => "mid=1_ref=ogpTW5fmXR"              |
  +--------+-------------------------------+
           |
           v
  +----------------------------------------+
  | GET /api/miniprogram/qrcode/image      |
  |   ?scene=mid%3D1_ref%3Dxxx             |
  |   &page=pages/read/read&width=280      |
  +--------+-------------------------------+
           |
           v
  +----------------------------------------+
  | 后端: & -> _ (若需要), 调微信生成图     |
  | 返回 image/png                         |
  +--------+-------------------------------+
           |
           v
  +----------------------------------------+
  | wx.downloadFile(url) -> tempFilePath   |
  | canvas drawImage(tempFilePath) 画海报   |
  +----------------------------------------+

  ---------- 用户扫码 ----------

  +----------------------------------------+
  | 微信: 打开 pages/read/read             |
  |       options.scene = "mid=1_ref=xxx"  |
  +--------+-------------------------------+
           |
           v
  +----------------------------------------+
  | App.onLaunch(options)                  |
  |   handleReferralCode(options)          |
  |   parseScene(options.scene)            |
  |   -> initialSectionMid, initialSectionId|
  |   -> ref 存 referral_code / 绑定       |
  +----------------------------------------+
           |
           v
  +----------------------------------------+
  | Read.onLoad(options)                   |
  |   parseScene(options.scene) -> mid,id,ref|
  |   与 app.globalData.initial* 合并      |
  |   -> 用 mid/id 拉章节, ref 已存         |
  +----------------------------------------+


---------- 3. loadContent(mid, id, accessState, prefetched) ----------

  +------------------+
  | loadContent(...) |
  +--------+---------+
           |
           v
  +----------------------------------------+
  | section = getSectionInfo(id)          |
  | setData({ section })                   |
  +--------+-------------------------------+
           |
           v
  +----------------------------------------+
  | prefetched 有内容?                      |
  +--------+-------------------------------+
           | Yes
           +-----> res = prefetched (不请求)
           |
           | No
           v
  +----------------------------------------+
  | mid ? GET /book/chapter/by-mid/:mid    |
  |    : GET /book/chapter/:id             |
  +--------+-------------------------------+
           |
           v
  +----------------------------------------+
  | res && res.content ?                   |
  +--------+-------------------------------+
           | Yes
           +-----> setData(content, paragraphs, partTitle, chapterTitle)
           |      if (canAccess): markSectionAsRead(id)
           |      setTimeout(drawShareCard, 600)
           |
           | No / 请求异常
           v
  +----------------------------------------+
  | 尝试 wx.getStorageSync(cacheKey)       |
  | 有缓存 -> setData 内容; 无 -> throw     |
  +----------------------------------------+


---------- 4. 参数来源优先级（onLoad 内 mid / id / ref）----------

  mid  = options.mid
      ?? parseInt(parsed.mid)
      ?? app.globalData.initialSectionMid
      ?? 0

  id   = options.id
      ?? parsed.id
      ?? app.globalData.initialSectionId
      ?? ''

  ref  = options.ref
      ?? parsed.ref
      ?? ''

  (解析 parsed = parseScene(options.scene)，支持 scene 内 & 或 _ 分隔)

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