My question is this : Without htaccess how can I prevent direct browser access to restricted php files?

I understand that Zen cart runs on php. Those files are accessed by scripts, not by pointing your browser directly towards them. Htaccess files uploaded to directories that contain php files prevent direct accessing them in this way. However Streamline will not allow me to use the "limit" keyword in my htaccess file rendering it functionally useless.

Did you read the article?

https://www.zen-cart.com/tutorials/index.php?article=235


I posted it for a reason. The issue is outlined in there.