My cart drawer or “add to cart” stopped working, why?

This is a JavaScript or AJAX failure. “Add to cart” that does nothing usually means the /cart/add.js request is failing, a console error is swallowing the click handler, or a stale cart bundle is out of sync after an app or theme update. We open the browser console, find the failing request or error, and patch the cart events so the drawer opens, quantities update, and the cart count refreshes correctly.