In do_update_embedded_data, we generate a variant update_message event, which has not been properly maintained and doesn't actually match the normal format. I fixed one issue in 00fd9af; but we should figure out how to make this event actually match the format of a normal update_message event, and then update the GET /events documentation with clear advice on handling it.

I'd like us to move that event to be more clearly match the format of normal update_message events, with perhaps some clear marker for these variant events.

@amanagr @showell I'd be interested in your thoughts on this.