I am certainly not a POE-person. Yet it seems to me that a good metaphor for what you're wanting is... that the worker, having dequeued a request, basically realizes that he can't process this request, and so it wants to put this request right back onto the queue where it came from:   not “another request just like the old one,” but “this very request.” The request-ID, the originator, the destination, everything ... is therefore unchanged.