Recently had an issue where a client was trying to link to a page using a content relationship field. He didn't realise he was linking to the page he was on, create a circular dependency but it wasn't clear to him as a content writer or to us as the development team what the issue was. Is there a way to stop users creating circular dependencies when creating documents?
As far as I can know, the only way from Prismic UI is to limit the custom type that you want to link to, and in fact, you can restrict to multiple custom types such as:
The drawback is that you have mentioned all the custom types you are linking to.
Please let us know if that doesn't correspond to your need,
Fares