【高级技巧】退避重试：幂等任务的三次递减尝试

local function retryTask(idempotent, task, maxTry)
    if not idempotent then
        sendmsg(nil, 1, "非幂等任务禁止重试。")
        return false
    end
    local delay = 200
    for attempt = 1, (maxTry or 3) do
        local ok = task()
        if ok then
            return true
        end
        if attempt < (maxTry or 3) then
            local t0 = os.time()
            while os.time() - t0 < math.floor(delay / 1000) do
            end
            delay = delay * 2
        end
    end
    sendmsg(nil, 1, "重试 " .. (maxTry or 3) .. " 次仍失败，转人工队列。")
    return false
end

local function resendMail(actor, ticket)
    actor = getplayerbyname(actor)
    retryTask(true, function()
        local done = getplayvar(actor, "HUMAN", "Mail_" .. ticket)
        if done ~= "" and done ~= nil then
            return true
        end
        sendmail("#" .. tostring(actor), 9050, "奖励补发",
            "补发单[" .. ticket .. "]。", "金条#1#0")
        setplayvar(actor, "HUMAN", "Mail_" .. ticket, 1, 1)
        return true
    end)
end