anchor.diff:  
   (define-command prompt-completion () ()
     (alexandria:when-let (completion-fn (prompt-window-completion-function (current-prompt-window)))
  -    (with-point ((start (prompt-window-start-point (current-prompt-window))))
  +    (with-point ((start (prompt-start-point (current-prompt-window))))
         (lem.completion-mode:run-completion
          (lambda (point)
            (with-point ((start start)
  
positive.code: (defun current-prompt-window ()
    (lem::frame-prompt-window (current-frame)))
  
  (defun prompt-window-start-point (prompt-window)
    (let ((buffer (window-buffer prompt-window)))
      (character-offset (copy-point (buffer-start-point buffer) :temporary)
                        (prompt-window-start-charpos prompt-window))))
  
negative.code:   (buffer-point (window-buffer (current-prompt-window))))
  
  (defun get-between-input-points ()
    (list (prompt-start-point (current-prompt-window))
          (buffer-end-point (window-buffer (current-prompt-window)))))
  
  (defun get-input-string ()
  