Should check that `annotation.user` matches the current user. See resources.py for the way to get the username and provider from `request.user` so that you can construct the acct:user@provider token that should be in the `annotation.user` field.

Also, `annotation.deleted` to know if it's deleted.

I would say maybe lets use this delete / redaction machinery we have for the undo actions. `if `downvote` in tags and annotation.deleted:` is the undo_downvote condition.