Stacked PRs

A stack is an ordered chain of branches rooted on a trunk. Each layer has one PR based on the branch below it, so a reviewer sees only that layer's diff.

(main) <- auth <- api <- frontend

Left is the bottom, right is the top. auth is based on main and merges first; frontend merges last. Foundational work belongs at the bottom, code that depends on it above. For how to choose the layers, read references/stack-design.md.

Pick one backend. Do not mix them.

• But stack when command -v but succeeds and but status exits 0. Do not run but setup.
• gh stack otherwise (the rest of this skill).

But stack