Audience question: in the marketplace example with buyer and seller engines, how do you avoid duplicating models? Adrian: that's a problem for 'developers who like to build things' rather than ship — extract shared behavior into modules or concerns and include them in per-engine models, or pick a different architecture that fits your app. In Avo's case there are no engine-owned models at all: Avo eager-loads the host app and picks up descendants of ApplicationRecord from the object space.