Consider @Aggregate annotation for packages.

[xenoterracide]

in my "book (comment)" I suggest the existance of an @Aggregate annotation that goes on a package to symbolize that is what the package represents and to prevent other aggregates from accessing things that should be contained to the aggregate only, requiring them to go through the AggregateRoot.

[odrotbohm]

We're not going to follow through with this suggestion for the following reasons:

• There's already an @AggregateRoot annotation to be used at a type. This is important, as that types designates an anchor point, able to establish rules like “refers to another aggregate root”. What constitutes the overall aggregate is an exercise of type reachability, then.
• Annotating a package as an aggregate is a substitute for the latter but lacks the definition of the former: the entry point into the aggregate, which is crucial to its definition. As soon as you add that information via @AggregateRoot, the benefit of the package-level annotation is gone.
• The prevention of the reference of entities declared for another aggregate in another aggregate's state is already covered by the entity type's definition, as Entity refers to the aggregate it's owned by. Invalid references are already detected by an ArchUnit rule.