Ah, I see ; put the whole dev toolchain in the container.

I use bindfs to mount the volume. I have a $HOME/Dev folders with WPProjectA, WPProjectB folders. Each has a volume subfolder mounted like that (the script has more variables but that's the gist of it):

    /usr/bin/bindfs \
        --force-user=johnchristopher \
        --force-group=johnchristopher \
        --create-for-user=www-data \
        --create-for-group=www-data \
        /var/lib/docker/volumes/WPProjectA-web/_data \
        $HOME/Dev/WPProjectA/volume

This setup allows using VSCode+xdebug and editing the code in the mounted volume while running the container and remote debugging.