How to make a function whose return type is inferred to be the same as an input function's

type Context = {
    abc: string,
    def: boolean
}

/* HAVE TO TWEAK THESE */
type Handler = (ctx: Context, ...args: unknown[]) => unknown;

function def<T extends Handler>(fn: T): T{
    // TODO
}
/* HAVE TO TWEAK THESE */

const fn = def(async function finalFunc({ abc }, a: string, b: number){
    // await new Promise(done => setTimeout(done, 2000));
    return 754;
})