AddSharedCalendarEvent
Add a copy of a calendar event someone shared with one of the user’s channels to one of the user’s Google calendars, asAdd to calendar on the event’s card does. Use it for a calendar event mention (blockName calendar) whose meeting is not on the user’s calendar; pass the mention’s documentId as eventId.
The copy is a snapshot, not an invitation: it keeps the real organizer and lists the user, accepted, as its only guest, while the meeting’s other guests and its join link stay out. Nobody is notified, and the copy does not change when the organizer changes the meeting. The user can change only its reminders and availability, or delete it. To be added to the meeting itself, the user asks the person who shared it from the event’s card.
Only Google calendars take a copy. When the user has one writable Google calendar the copy goes there; when they have several, ask which one and pass its calendarId from ListCalendars. The result is the user’s copy, whose eventId UpdateCalendarEvent and DeleteCalendarEvent accept.