I have no idea what string reference could be used when steps come from Task?

Oh I see, you are correct, when it comes to Tasks the assumption is your are passing strings (with selectors on the strings, i.e. the curly brackets) but there is no fancy serialization/deserialization as you have with pipelines from decorators / functions. The reason for that is that the Task itslef is a standalone, there is no way for the pipeline logic to actually "pull data" from it and "pass" it to the other Task. The assumption is the Task itself was designed with in/outs in the first place. Does that make sense ?