I talk a bit about this in T61#968.
So there are five main parts to this equation.
- Drone needs to be able to authorize Phabricator users using OAuth.
- Phabricator needs to trigger Drone
- Drone needs to receive this trigger
- Drone needs to send some kind of response back to Phabricator
- Phabricator needs to receive this response
Some work has been done for 1 which is mentioned in the description.
Much like T58 a Herald rule can trigger Harbormaster to run a build when a commit is made. For 2 during the build process Harbormaster can trigger an HTTP request to Drone but as far as I can tell there isn't a way to customize what it sends. So for 3 either there will need to be a separate trigger for each repository or Drone will need to be able to query Phabricator.
For 4 and 5 Drone can send a webhook to Harbormaster which can wait to receive a HTTP response during the build process, but that only indicates a pass/fail. In order to get more context Drone would need to use the Conduit API.