Hi Leo,
The first suggestion, to add to org-babel-maxima--output-filter-regexps
does fix the src block you ask about here.
However, the regexp doesn't match for other maxima tests. For example:

#+name: ob-maxima/batch+verbatim
#+begin_src maxima :results verbatim :batch batch :cmdline --quiet
(assume(z>0),
integrate(exp(-t)*t^z, t, 0, inf));
#+end_src

#+RESULTS: ob-maxima/batch+verbatim
#+begin_example
(%i1) (linenum:0,
(%i1) (assume(z > 0),integrate(exp(-t)*t^z,t,0,inf))
(%o1)                            gamma(z + 1)
#+end_example

Best,
Ben

On Wed, Dec 11, 2024 at 7:02 AM Leo Butler <Leo.Butler@umanitoba.ca> wrote:

> On Tue, Dec 10 2024, Benjamin McMillan <mcmillanbb@gmail.com> wrote:
>
> > Hi Leo,
> > I get the following output:
> >
> > #+RESULTS:
> >
> > #+begin_example
> > (linenum:0,
> > #+end_example
> >
> > and from *messages*:
> >
> > Executing Maxima source code block
> > maxima -r \(linenum\:0\,\
> >
> batchload\(\"/var/folders/f5/6nrph1812wdf0nlg4ddcs_580000gn/T/babel-wImUPJ/maxima-Swf2M2.max\"\)\)\$
> >  --very-quiet
> > Wrote
> >
> /var/folders/f5/6nrph1812wdf0nlg4ddcs_580000gn/T/babel-wImUPJ/ob-input-Rbgtzp
> > Code block evaluation complete (took 0.1s).
> >
> > The contents of that file (which I also attach) are:
> >
> > build_info();
> >
> > If there's more information I can give, just let me know.
> > Thanks,
> > Benjamin
> >
> > On Tue, Dec 10, 2024 at 9:17 AM Leo Butler <Leo.Butler@umanitoba.ca>
> wrote:
> >
> >> On Mon, Dec 09 2024, Leo Butler <Leo.Butler@umanitoba.ca> wrote:
> >>
> >> > On Sun, Dec 08 2024, Ihor Radchenko <yantar92@posteo.net> wrote:
> >> >
> >> >> Benjamin McMillan <mcmillanbb@gmail.com> writes:
> >> >>
> >> >>> This outputs
> >> >>> #+RESULTS:
> >> >>> | (linenum:0, |
> >> >>> |           4 |
> >> >>>
> >> >>> I suppose the issue is the "linenum:0". In fact, running any of the
> >> test
> >> >>> src blocks does that, e.g.
> >> >>> #+begin_src maxima :results verbatim :batch batch
> >> >>> (assume(z>0),
> >> >>> integrate(exp(-t)*t^z, t, 0, inf));
> >> >>> #+end_src
> >> >>>
> >> >>> #+RESULTS:
> >> >>> #+begin_example
> >> >>> (linenum:0,
> >> >>> (assume(z > 0),integrate(exp(-t)*t^z,t,0,inf))
> >> >>>                                  gamma(z + 1)
> >> >>> #+end_example
> >> >>> This does not match the (should (equal ...)) in test-ob-maxima.el
> >> >>>
> >> >>> I don't know maxima, and haven't made any explicit modifications
> >> regards
> >> >>> it, so I don't know why my setup would be outputting linenum:0
> >>
> >> Benjamin,
> >> When you execute your source code block, ob-maxima prints the shell
> >> command as a message. Could you copy that shell command from *Messages*
> >> and send it, along with the batch file that ob-maxima creates?
> >>
> >> Thanks,
> >> Leo
> >>
> >> >>
> >> >> Setting linenum was introduced in
> >> >> https://list.orgmode.org/orgmode/87jzsrai3x.fsf@localhost/
> >> >>
> >> >> It clearly does not affect Linux, but Maxima on MacOS appears to have
> >> >> slightly different behavior.
> >> >>
> >> >> I am CCing the author of the original patch that introduced this
> >> setting.
> >> >> Leo, maybe you have some insight?
> >> >>
> >> >> Unless we can do something to solve the problem on Mac, I am
> tentatively
> >> >> inclined to revert the linenum part of the patch, so that ob-maxima
> is
> >> >> not broken on MacOS.
> >> >
> >> > Benjamin,
> >> > Could you include the output of
> >> >
> >> > #+begin_src maxima :results verbatim
> >> > build_info();
> >> > #+end_src
> >> >
> >> > , please? I think the bug is in the Mac build of Maxima, but I need
> more
> >> > information to figure it out.
> >> >
> >> > Best,
> >> > Leo
>
> Hi Benjamin,
>
> Let me preface my requests by saying that I do not have access to a Mac,
> and the problem you are seeing seems to be Mac-specific, so I am
> searching in the dark for a solution to the problem.
>
> I have a couple ideas.
>
> * First idea
> ** Add the regexp =^(linenum:0,= to
> =org-babel-maxima--output-filter-regexps=
>
> #+begin_src elisp :exports none :results raw
>   (add-to-list 'org-babel-maxima--output-filter-regexps "^(linenum:0,")
> #+end_src
>
> ** Evaluate your Maxima code block
>
> #+name: max
> #+begin_src maxima :results raw :batch batch
>   (assume(z>0), integrate(exp(-t)*t^z, t, 0, inf));
> #+end_src
>
> If all goes well, you should see the output:
>
> #+RESULTS: max
> (assume(z > 0),integrate(exp(-t)*t^z,t,0,inf))
>                                  gamma(z + 1)
>
> Please evaluate these code blocks in an Org buffer and tell us how it
> goes.
>
> * Second idea
>
> We could introduce a customization variable, e.g.
> org-babel-maxima-batch/load-format-string, whose default is the current
> value is "(linenum:0, %s(%S))$". You could change that to "%s(%S)$".
>
> I would prefer to see if the first idea works for you, though, before
> pursuing this.
>
> TIA,
> Leo