desktop and panel toolboxes are only visible in "edit mode"
edit mode can be triggered by
* long press in desktop
* context menu action
* dbus property (to be eventually used by systemsettings)
The desktop toolbox becomes a "toolbar" with just few selected actions
the presence of that toolbar both fullfills "long press should usually show some
contextual actions" and being a very visible hint that "we are now in edit mode"
toolbox is still movable around in case would obscure any important stuff where it's
by default
depends from D24263 and D24264