Warp: client-side filters for waiting for "right" request or enriching several requests

When client can fire several requests at time, Warp enriches the first one which comes.

Ideally, user should be able to select the appropriate request based on constraints:

API proposal:

Warp.execute(new ClientAction() { ... })
    .filter(RequestFilter.extension(Extension.XHTML))
    .verify(...)

Additionally, several requests caused by one action should be verified with various assertions.