How to Expose a Singleton Landing Page to the GraphQL API

import S from "@sanity/desk-tool/structure-builder";

export default () =>
  S.list()
    .title("Content")
    .items([
      S.listItem()
        .title("Settings")
        .child(
          S.editor().schemaType("siteSettings").documentId("siteSettings")
        ),
      S.listItem()
        .title("Home Page")
        .child(S.editor().schemaType("index").documentId("index")),
      ...S.documentTypeListItems(),
    ]);