I’m not sure if there is validation in mutation inputs. I thought it was param-related only. Need to check.
I did a small search about this, no luck even in the GraphQL spec. We need confirmation. If there is validation for mutation objects via input.
Also, you may try to use “strict mode” for mutation. It is a global flag that forces any mutations(DQL, not sure if GQL bypasses it) to follow the DQL schema. It throws an error if the mutation doesn’t reflect the schema.