On my Phabricator instance I run builds on repositories that are directly tracking third-party projects. The purpose of these builds are so that I can monitor when that project makes changes that might be incompatible with the projects that I'm using them in, and to highlight those compilation errors or tests. When the builds or tests fail, this indicates that I need to update my code which is consuming that library.
However since I'm not the author of those commits, I don't get build failure notifications.
There doesn't appear to be a Herald rule for "Harbormaster Builds", and I don't want to be CC'd on every commit (I only want to be notified when a build of a commit fails, not for any other event).