We will support a stack that is fully contained within a single fork, where the entire stack targets the original repo.
For example, a contributor who has a fork (user/buzz) of the original repo (org/buzz) could create the following stack:
``` frontend → PR #3 (base: user/buzz:api-endpoints) api-endpoints → PR #2 (base: user/buzz:auth-layer) auth-layer → PR #1 (base: org/buzz:main) org/buzz:main (trunk) ```