It's a very simple hook to listen to the Phabricator feed, figure out who is subscribed to the object that is the subject of the feed, and ping them in Slack. The goal was to make it stateless so it could be used as an AWS lambda. It's done wonders for our review response time.

The plugin approach will probably work fine for us. Thanks @epriestley.

I believe I described the root problem already, but just to be extra super clear:

Not exposing email addresses with user.query makes it difficult to do things like associate phabricator users with slack users for bots that post phabricator notifications to slack :(