I have site v7 that is using umbraco graphql package. I have doctype alert which I can get using query like:

{ content {
byUrl(url: "/alerts/test/") {
  ... on Alert {
    _contentData {
      name
    },title
    summary
  }
}}}

What i want to do is before render for the summary field which is rich text edit field modify img tag. I have service to do this however I am unsure how to tap in the rendering process of graphql to intercept. I have for now got project using actual source code of umbraco graphql project.

Would I need to modify StringValueResolver and create my own StringGraphType that does the transformation?

        public override Type GetGraphQLType(PublishedPropertyType propertyType)
    {

        if (propertyType.PropertyTypeAlias == "summary")
        {
            return typeof(CustomStringGraphType);
        }

        return propertyType.ClrType == typeof(string) 
            ? typeof(StringGraphType)
            : typeof(ListGraphType<StringGraphType>);
    }

And in my CustomStringGraphType override

    public override object Serialize(object value)
{
  return value;
}

and do my transformation there?