I like the concept of the autoactivate and the return.
From a UML perspective, I would have liked that the "return" or the "A <-- B" would also use or work with the <<-- arrow. I always try to indicate in invocations whether they are asynchronous (->>) or synchronous (->) and for a synchronous call the return should be (<<--). The return does not give that type of arrow, nor does the <<-- work together with autoactivate.
Thanks.