How to merge existing cache items in read function with pagination. ACL3

Help
,
1 
query MagicFeed($limit: Int!, $offset: Int!) {
  magicFeed(limit: $limit, offset: $offset) @connection(key: "magicFeed") {
    ... on Product {
      id
      __typename
      name
      price
      defaultImage
      formatedName @client
      formatedPrice @client
      shop {
        id
        name
        avatar
        formatedShopName @client
      }
      isBookmarked
    }
    ... on Category {
      id
      __typename
      name
      image
    }
  }
  
  mainCategories {
    id
    __typename
    name
    image
    subCats {
      id
      name
      image
    }
    isSubCat
  }
}

That was my Query, Here i am querying for magic feed and main categories from the server.
and inside my inMemeryCache.

export const cache: InMemoryCache = new InMemoryCache({
  typePolicies: {
    Query: {
       fields: {
         readMainCategories: {
          read(mainCategories, { readField}){
            return readField<MainCategoriesQuery[]>('mainCategories') ?? [];
          }
        },
        magicFeed: {
          keyArgs: false,
          read(existing, {  args: { offset = 0, limit = existing?.length } = {}, readField }: any) {
            const mainCategories =  readField('readMainCategories')) || [];
            newFeed = existing ? existing.slice(0) : [];
 
            // i would like to return a new array with first element of the array 
            // being main category results returned from the cache and return the list

            return existing && existing.slice(offset, offset + limit);
          },
          merge(existing, incoming, { args: { offset = 0 } }: any) {
            const merged = existing ? existing.slice(0) : [];
            for (let i = 0; i < incoming.length; ++i) {
              merged[offset + i] = incoming[i];
            }
            // console.log('magicFeedMerged', merged);
            return merged;
          },
        },
       }
    }
  }
})

inside the read function, i would like to return a new array with first element of the array being main category results returned from the cache and return the list. Is this doable, Also with read function pagination doesn’t work for me.