*and not only paste, but write, in the source file, the new definition, re-compile it (C-c C-c), and resume execution from a stackframe before this call. (a clarification for folks who would think we must paste in the REPL)

That's useful not only for breakpoints but for errors. We can fix an error without re-running everything from zero. https://www.youtube.com/watch?v=jBBS4FeY7XM