[ordinary]

I don't use Deft, so YMMV, but it sounds like you're looking for visual-line-mode.

Interactively:

  M-x visual-line-mode

Or in your .emacs:

  (add-hook 'deft-mode-hook 'enable-visual-line-mode)

You'll probably need to set deft-line-width to some number that's larger than the most columns you ever have in a frame, because from a quick glance it looks like Deft has some magic of its own.