Handlers aren't meant to be nested like this. That is, it's always going to break this way, because the handler needs to live as long as the request and response, so creating a sub-handler is not ever going to live long enough.

So yes, the solution is to not implement Handler for your UserIndexHandler; then you can just call it.

I bet there's something larger you could do as well, but I don't have enough experience with this interface to give good advice. Hyper's undergoing a huge docs drive for 0.11; I'm sure that'll help.