I'm creating a Google Calendar add-on and I was wondering if I could implement drag and drop support, to drag an event from my add-on to the calendar.
The Google Tasks add-on supports it (you can drag and drop tasks onto the calendar), but it's unclear whether it's using public or private APIs to achieve it.
Is this possible?
Calendar add-ons (or for that matter, any Workspace add-on) don't provide this kind of functionality. Add-ons sidebars are based on Cards, and these don't contain any element that can be dragged outside the card-based interface (see class CardService for a reference of what you can do with cards).
If you want to see this implemented, I'd suggest filing a feature request in Issue Tracker.