I need to limit the execution time of arbitrary zsh functions. Is there a
way to achieve this? I'm ok with just adding a time limit to all the
external commands, but I do not know how to do that. (I don't want to
manually prefix all my commands with the GNU timeout command.)

On a sidenote, I would also like to make the shell stop forcefully (like
when a glob fails) if it doesn't find an external command. I thought maybe
these two problems might have similar solutions. Is prexec viable for them?
Does preexec even work for noninteractive scripts?