Oops, forgot to reply all on my last message. Attached is the patch.

On Wed, Nov 4, 2020 at 8:44 PM Stefan Monnier <monnier@iro.umontreal.ca> wrote:
>
> > It looks like I was able to make progress today. Just by modifying
> > server.el, I've gotten `emacsclient -ce "..."` to create a new frame
> > based on the currently selected frame's terminal when called in a dumb
> > terminal.
>
> Great!
>
> > Unfortunately, the command for calling ediff is still very
> > unpleasant:
> >
> > emacsclient -ucF "((delete-frame-on-ediff-quit . t))" \
> >   -e "(ediff-merge-with-ancestor \"${local}\" \"${other}\" \"${base}\"
> > nil \"${output}\")" \
> >   -e "(add-hook 'ediff-quit-hook (lambda () (when (frame-parameter nil
> > 'delete-frame-on-ediff-quit) (delete-frame))))"
>
> I think the problem is that emacsclient lacks the equivalent of `-f`,
> i.e. calling a particular ELisp function where the remaining arguments
> can be consumed by that function.  That would solve the problem of
> quoting (your above script will stumble when encountering
> a file name with quotes in it or with a final backslash).
>
> > So perhaps introducing a wrapper script for ediff merges would still be useful.
>
> We should be able to add a convenience `batch-ediff-merge-with-ancestor`.
> Bonus points if you manage to make it work with `emacs --batch -f` as
> well as with `emacsclient --<newflag>`.
>
>
>         Stefan
>