this is empty for now, but i'll be working here for the next day or two to try to sketch out what "externalizing target fields" ie, "sources as a product" should look like: https://docs.google.com/document/d/102EFbwk6cpM9-_4ZSYhMQYA0zL1UKbXzW-DCd8KsFeg/edit?usp=sharing