家底（家庭总账）

const money = (v, label, max = 1e12) => {
  if (typeof v !== 'number' || !Number.isFinite(v) || v < 0 || v > max
      || Math.round(v * 100) / 100 !== v)          // 恰好两位小数，多一位都拒
    fail(label + ' 必须是范围内的有效非负金额（最多两位小数）')
  return v
}
const date = (v, label, empty = false) => {
  if (empty && v === '') return v
  const parsed = /^\d{4}-\d{2}-\d{2}$/.test(v) ? new Date(v + 'T00:00:00Z') : null
  if (!parsed || parsed.toISOString().slice(0, 10) !== v)   // 往返不一致即非法
    fail(label + ' 不是有效日期')
  return v
}

async function acquireLock() {
  try {
    const fh = await open(lockPath, 'wx', 0o600)
    await fh.writeFile(String(process.pid)); return fh
  } catch (e) {
    if (e.code !== 'EEXIST') throw e
    const pid = parseInt(String(await readFile(lockPath, 'utf8')).trim(), 10) || 0
    let alive = false
    if (pid > 0 && pid !== process.pid) {
      try { process.kill(pid, 0); alive = true }
      catch (err) { alive = err && err.code === 'EPERM' }   // EPERM = 存在但没权限，也算活着
    }
    if (alive) throw new Error('数据目录已被占用（PID ' + pid + ' 仍在运行）')
    await unlink(lockPath)                                  // 僵尸锁：持有者已死，直接接管
    const fh = await open(lockPath, 'wx', 0o600)
    await fh.writeFile(String(process.pid)); return fh
  }
}

const keepDir = join(dataDir, '..', '..', '..', '.jiadi-keep')   // dataDir = <卷>/@appdata/<app>/data
await mkdir(keepDir, { recursive: true, mode: 0o700 })
await writeFile(join(keepDir, `ledger-before-${tag}-${stamp}.json`), current)

// 网关头只在显式信任网关时才读，否则一律走正常登录
function readGatewayIdentity(headers, trustGateway) {
  if (!trustGateway) return null
  const uid = String(h['x-trim-userid'] || '').trim()
  if (!uid) return null
  return { uid, username: ..., isAdmin: ... }
}