`RpcStub<T>` doesn't preserve tuple type - turn `[number, number]` tuple into array `number[]`

[codehz]

playground link: https://www.typescriptlang.org/play/?#code/JYWwDg9gTgLgBDAnmApnA3nASmAxgZRgFcAjOAXzgDMoIQ4AiXAQzADsB3FEhgKF4AmKXABtmUNKOYBnaXAAqKafHS846uAHMUMAGrMRRFAAoAlAC44AbTZEQJFFAA0cW-ccBdXuX5JUcAA84AF44AEEOZmAYFAEAHiwdIig2eWQUBLxCUjjFZQA+KwZtPQMjBg98-N4AehqNAD0AfiA

import type { RpcStub } from "capnweb"

declare class Test {
    getValue(): [number, number]
}

type x = Awaited<ReturnType<RpcStub<Test>["getValue"]>>
// number[] & Disposable

Expected Behavior

preserve the tuple type

Actual Behavior

All tuple turns into array, which make some types incompatible.