How to limit line item quantity with Functions?

How can I recreate a Shopify Script that limits the quantity of a line item?

I don’t want to block checkout with a Validation Function.
I simply want to reset the quantity if a user attempts to increment it past 1, via theme or console commands.

Does such an ability exist in Functions yet?

perhaps you can use theme app block app embed block on the cart page with the cart API. Call the Cart API if the item quantity passes 1.