WebDriver is very similar to what I need, but it looks like it requires Epiphany to be brought up in “automation mode”, and Epiphany in automation mode cannot be used normally by the human user. When I try, it rejects user/chrome interactions, and displays “Web is being controlled by automation”.
My hope was for some way to use an Epiphany instance as per normal, but also invoke scripted behavior on demand, in-session.
Thank you for the suggestion, though. WebDriver is tantalizingly close to “the right thing”.