For statistics and audit reasons it could be useful to store some of these values in task or repo itself.

Easiest way would be to provide event via newRepo. It means changing tag_changed_since_event to return event_id instead of bool.

It needs little bit smarter SQL and it also conflicts with possible speed optimization (use of EXISTS instead of LIMIT).

I'm not sure if it is worth the potential benefits of better kojira performance monitoring, so marking as discussion.