It sounds like you are starting from some memories about fibers/threads in desktop programming and trying to map an exact equivalence. I remember that world. Don't think that way. Fibers are more about not waiting around for an answer that could come any time.
I bet if you take smaller steps, think less, and just get some HTML/js to do what you want, then come back here when you hit a stopping block, you will make progress.
Ownership of items, for example, is commonly expressed by a field in a document, ownerid, matching current userid