I think it's valid since Life, in this case, extends Box of Chocolates and therefore "is a" Box of Chocolates. If Life had implemented the same interfaces or extended the same parent class as Box of Chocolates, then it would be a @simile as Life, in that case, would be "like a" Box of Chocolates.
Looks fun. I assume it's still up to the application devs as to how they handle those annotations then (say on a build server or when the docs are generated)? Unless I'm missing something, there doesn't appear to be any direct effect of using them other than the meta-data that they add.
Edit: looks like "gag-agent" is there to react to the annotations, but it's not clear to me where/how that would work
It's mostly there to send messages to your fellow programmers, it seems. The instrumentation jar will enforce the behaviors of the annotations under the Enforceable category.
Something that almost seems as though it wouldn't be completely out of place in a production codebase (though you'd probably want to ensure that they were elided or at least renamed before shipping :P).