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.