Restore Shopify Cart Code

I experimented with some AI-generated edits to my Shopify theme and my checkout cart has been unstable ever since. The main symptom is that items in the cart no longer update correctly—quantities stick, removals don’t register, and customers can’t see accurate totals.

What I need:
• Roll back or manually reinstate the pre-edit code for the cart and any related liquid, JavaScript, or schema files.
• Verify, in a live test order, that item quantity changes, removals, and additions reflect instantly and carry through to checkout.
• Give me a quick note on what went wrong so I can avoid re-introducing the same issue.

I haven’t seen payment or shipping errors; the cart update bug is my only concern right now, but please flag anything else you notice while you’re in the code. Familiarity with Shopify Liquid, cart.js, and theme version control will make this a quick win for both of us.