The outline that exists today, pinned to the view when the selection runs past it. The frame itself becomes the message: what you selected continues beyond the screen.
Smallest possible change. Same code path as today, clamping the four projected corners before the path is built.
Bounded by construction. The frame can never exceed the viewport, so the dash count is fixed no matter how deep you are.
Says nothing about WHICH object is selected when several overlap, and reads as chrome rather than as a property of the drawing.