Hi Alex,
Generally speaking, Nanoflows are running in the client, they don't communicate with the backend, unless a connection is needed (Microflow call or data retrieval/sending).
So the thrown errors are not being logged on the server.
I think your best option would be the one you described. Use error handling to log important errors to the server.
Hope this helps!
P.S. Could be a great improvement to nanoflows though: Enable serverside error logging..