Adding a note (either tool) always ended in a 401 for a logged-out viewer — the write-only affordance just wasn't hidden yet, unlike GpxPanelControl's own upload/new-folder buttons, which already are. NotesControl isn't added to the map at all when logged out (its whole purpose is writing); MeasureControl's "Save as note" button is hidden but the tool itself stays usable for plain measuring either way.