Zend certified PHP/Magento developer

magento 2: debug to addtocart simple product for one qty in stock

I am trying to figure out the flow add to cart item.

Note: before add to cart my cart is empty

I have a simple product and it has one qty and product inStock is yes, it does not go prepare function in following path MagentoQuoteModelQuoteItemProcessor.php because I put die() function in prepare function for testing ,it did not call die() function and product added to cart successfully, but how ? and then clear my shopping cart and when I change the qty from 1 to 2 for same product and save it then I try to add to cart it goes to prepare function in following file MagentoQuoteModelQuoteItemProcessor.php

but how differently works based on qty ?

Please help me on this
I am using magento2.4.0