If you are triggering a CI workflow from Github, from my understanding Graphite doesn't have the ability to find future job ids. We do have our own set of CI optimizations here that could be helpful:
https://graphite.com/docs/stacking-and-ci
I would want to repro whether triggering CI through label on Graphite would then link the CI job to the PR. You're welcome to give this a try and I will try this next week