I'm writing a PHP script to communicate with Amazon for their fulfillment service. The script needs to access information that Zen Cart stores in the $order variable.

Q1) How does Zen Cart preserve and make a variable like $order accessible across pages?

I'd prefer using the $_SESSION variable to pass the info. In comparison, extracting the necessary info and passing via GET seems quite cumbersome. Unfortunately, adding session_start() to my script gives me a new, empty $_SESSION variable. I call the PHP script via jQuery from the file tpl_modules_shipping_estimator.php.

Q2) Any idea why session_start() creates a new session instead of resuming?