You have this almost correct. Sourcing for interactive mode has
nothing to do with it. It always applies to the scriptname argument
passed to a new zsh, so it has to be in effect before zsh searches for
the script.

I may not be following you here.

If I have a script at ./dir/some_script and I do:

> PATH=./dir

> setopt pathscript

Then do

> /bin/zsh some_script

It will not look for the script in $PATH as far as I can tell and fails with zsh: can't open input file: some_script

You are saying my last command above should work with pathscript on?