# File lib/sup/modes/line-cursor-mode.rb, line 56
  def ensure_mode_validity
    super
    raise @curpos.inspect unless @curpos.is_a?(Integer)
    c = @curpos.clamp topline, botline - 1
    c = @cursor_top if c < @cursor_top
    buffer.mark_dirty unless c == @curpos
    @curpos = c
  end