Better breaking schema change descriptions for union type member removal

[n1ru4l]

We already have some descriptions about why a breaking change is a breaking change. E.g. here in a schema version:

Some Hive users were confused about removing a union member being a breaking change.

Quick question about breaking change detection in Hive. I’ve removed an element from a union, no clients are currently requesting any fields on that type, but it shows as a breaking change. Is this expected?

We answered it the following way:

so the reason it is considered breaking is that it affects the __typename field. So from our system perspective, it's not safe to accept a deletion of a union member as it may affect the value of __typename and potentially break your GraphQL consumers (an example would be a React component that renders a child component based on the value of the __typename field, a feed that renders an Image post or a Text post).

Instead of people having to reach out to us, this information should be available within the changes UI.