委托回执：提交与返回一一配对

-- 错误：只发不等回执，重复提交无感知
function sendDeal(goodsId, price)
    postDealing(goodsId, price)
    waitForever()
end

local pending = {}
local seq = 0
local function sendDeal(goodsId, price)
    seq = seq + 1
    pending[seq] = {goods = goodsId, price = price,
        at = os.time()}
    postDealing(seq, goodsId, price)
end
local function ackDeal(seqNo, ok)
    local item = pending[seqNo]
    if item == nil then return end
    pending[seqNo] = nil
    if ok then
        refreshList()
    else
        sendmsg(me, 1, "委托被退回，请重试")
    end
end