I missed the `decorate` call in the deploy()-method, ...

Yea this is a programmatic (test-only) way to enable them as if you had beans.xml. If you just used @Priority, it should work even without it.

However, I am still struggling with a decorator which only started working after I moved default impls to the abstract class

So you still have the problem? Could you try tackling the reproducer so that it shows the issue?

You wouldn't happen to have any pointers...

You mean debugging proxy/subclass creation? Interception/decoration itself is "just" invoking a method on the generated proxy then.