atlas-client.ts

// zeus.ts
interface User {
  firstName: string,
  lastName: string
}
interface Entity {
  id: string
}

type UserEntity = User & Entity;

// atlas.ts
type GetUserQuery = {
  getUser: {
    id: string,
    firstName: string,
    lastName: string
  } | null,
}

// some zeus based service
const myResponse: GetUserQuery = { getUser: { id: 'foo', firstName: 'bar', lastName: 'baz' } };
const myUser: UserEntity = myResponse.getUser;