Good question! They get removed, like faithful retainers; I low-key designed this faction supposing the use of Exiles and Partisans, because I love that interaction :)
Scrap! and Scrouge! are definitely a bit weird, and I intend on adding better text. Your former guess is correct: they're supposed to be a free action, as long as they are on the top of the Blueprints stack.
I'm glad the infographic is helpful! And thanks so much for the great comment :)