A conflict low in a stack blocks merging PRs above it, even when they merge cleanly

**The problem**

Say `main ← PR1 ← PR2`. PR1 has merge conflicts against `main` and can't be merged. PR2 against PR1 is completely fine — no conflicts at all.

Merging is all-or-nothing for the whole chain up to `main`: if any PR in the stack can't be merged, none of them are. So even though PR2's changes are ready and conflict-free relative to PR1, there's no way to merge it — it's stuck behind PR1's unrelated conflict with `main`.

**Impact**

A single conflict low in a stack blocks everything built on top of it, even work that's fully ready and has nothing to do with that conflict. Teams end up stuck waiting on someone to resolve the bottom PR's conflict before any of the PRs above it can move forward, with no way to make progress on the parts that are actually ready.

This also blocks deploying feature branches to a staging environment for testing — a common practice at many companies. In this scenario, the feature branch is PR1's branch (the one with the conflict against `main`): deploying it to staging means merging it, and that merge is exactly what's blocked, so the branch can't be deployed until the unrelated conflict is resolved.

Comece rastreando como gh-stack determina se pull requests empilhados podem ser mesclados e como lida com branches destinados à implantação em staging. Defina o comportamento desejado para um pull request sem conflitos acima de um pull request com conflitos, incluindo como sua prontidão para merge e seu caminho de implantação devem ser representados. Considera-se concluído quando os pull requests superiores podem avançar de forma independente sem ignorar incorretamente suas dependências.

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