Currently, dependent is not handled when adding a Herald rule to trigger build plan on Differential Revisions.

Suppose Dyyyy depends on Dxxxx which is not closed yet.

A build plan triggered by Dyyyy will likely to fail. The solution here could be like below

1, only trigger the build plan for Differential update without any denepedent (Thus Dyyyy will not trigger the build plan)
Here, arcanist need to be able to set the dependent status (NO, YES/Dxxxx) when generating Dyyyy via "arc diff"

2, trigger the build plan for Dyyyy when Dxxxx is closed