Guest cart issues - set cookie in custom GraphQL mutation

Main question: How can I set response headers from a custom GraphQL mutation resolve function?

Longer version: Hello! I'm making a Cart collection that can optionally be assigned to a user. Access checks will allow a user to access the cart assigned to them, and allow anyone to access a cart that they know the ID of and that hasn't been assigned to a user.

I'm making custom GraphQL queries and mutations, but I need a way to get the cart ID from the user, and I don't want this to be a frontend responsibility. Thus, I'd like to pass and read a cart cookie. Within the resolve function, I can readily read the cookies sent from the client, but can't figure out how to set a cookie.

For an example use-case: when a guest calls the addCartItem mutation, if no cart cookie is received I'd like to create a guest cart (no associated user) and set a cookie in the response header with a JWT token that contains the cart ID. I see that the context arg exists in the resolve function, but there doesn't seem to be a method for setting headers on the context.res object. Can anyone point me to a way to do this?