Constant SCROLLBACK_WARNING 

pub const SCROLLBACK_WARNING: &str = "that was a terminal, so the key is now in the scrollback, in your \
     multiplexer's buffer and in any session log — none of which this command \
     can reach. Treat it as exposed unless you clear all three, or rotate it.";

What the caller prints when the key landed in a terminal.

Here rather than in the binary so the rule and its wording sit beside the code that decides it, the way every other message in this module does.