So we dropped restart safety (multiple returns from @vector-map) after all?  (I thought John's message that he

added explicit language to @vector-map.) 

We could leave it out---in that case, since the current @vector-map reference implementation isn't restart-safe,   

I'd imagine it would be de-facto that @vector-map won't be restart-safe.

If it's an overlook, we need to fix reference implementation as well, which I can make PR.