Currently there is only one commit-related event called `diffusion.didDiscoverCommit`, which is fired after commit record is inserted to database. Unfortunately at that time the commit isn't parsed yet so if any custom code wants to look upon files, changed in that commit it can't.
I propose to add `diffusion.didParseCommit` event, that will be fired at the end of `PhabricatorRepositoryCommitParserWorker::doWork`, where we know at 100% that all commit data is available.
I suppose not much coding needs to be done (define event constant in one place and fire the event in another place), so I can do implement it as well.