foo.js

const query = gql`
  query FetchWhatMyAppNeeds {
    # run 1
    tasks {
      id
      details {
        date
        title
        # run 2
        header @client # virutal field (date + title)
      }
    }

    # this is never applied because it isn't below
    # a root field, so the resolver never runs for it
    # run 2
    todos @client {
      id
      detail {
        title
      }
    }
  }
`;

const mutation = gql`
  mutation addTodo($title: String) {
    addTodo(title: $title) {
      id
      detail {
        title
      }
    }
  }
`;

const defaults = {
  todos: [],
};

const resolvers = {
  Mutation: {
    addTodo: (_, { title }, { cache }) => {
      cache.writeData({ todo: { id: 1, detail: { title } } });
    },
  },
  Detail: {
    header: ({ date, title }) => `${title} is due on ${date}`,
  },
};

const link = withLinkState({ cache, defaults, resolvers });