Hey,
There is no reference because they have been dropped from the framework. I saw no mention of a preferred solution, but I saw plenty of comments from solnic and others from core team, about leaving the choice up to the developer.
Since a large portion of Hanami is built upon dry-rb family of gems, I would assume dry-monads is a nice fit, I however usually prefer to build something upon POROs and see where it gets me. After spending few years with trailblazer operations I aim for the simplest, minimalistic solutions first. Might be an approach that fits the hanami philosophy.
This is the only other topic directly touching on interactors not being transfered from 1.3 to 2.x