Where to place a definition for something that is not a model, route, controller, view, component etc

I want to create a type extended from DS.AdapterPopulatedRecordArray (could as well be just an ArrayProxy, the fact that I’m using a DS private type is not relevant, I hope), which I’m going to re-use in several route models. I’m a bit at a loss where to put it in the ember-cli app tree. app\model seems the only one that is not obviously wrong, but it still does not feel right. Is there a guidance for this?

I guess it doesn’t matter, since there is no magic auto-load path. Place it in widgets\gadget-sprocket.js and then use it with import GadgetSprocket from "app\widgets\gadget-sprockets"