Is there a way to force a new PR to stack on top of an already-merged PR?
Motivating scenario:
1. I have a stack of 3 PRs (A, B, C).
2. I merge A and B, but C is still in review.
3. I realize I need to add a new PR between B and C. Let's call it B2.
4. When I submit the stack with the new PR, B2 and C become a separate stack, disconnected from A and B.
I would love to be able to tell Graphite that the new B2 should stack onto B, either when submitting or by "restacking" them after-the-fact.