attac-t Skill: Craft PR Stack
"A stack is a merge order. Impose one only where the work already has one."
When
| Stack | Branch from main |
|---|---|
| The second change needs the first | Neither needs the other |
| Both edit a file every change edits — manifest, lockfile, changelog | They touch different files |
On that second row a green gate is not evidence: each branch passes alone while the merge of both is wrong.
A stack imposes a merge order, and an order nobody needs is one somebody has to wait for.
The Protocol
Branch from the open PR you depend on, and target it. Do not branch from main and wait.
gh pr create --base <parent-branch>
When the parent moves, replay the child's own commits onto it:
git rebase --onto <parent-branch> <old-parent-tip> <child-branch>
git push --force-with-lease origin <child-branch>
Once the parent is rewritten, nothing computes <old-parent-tip>. Read it from the reflog:
git rev-parse <parent-branch>@{1}, or origin/<parent-branch>@{1} if someone else force-pushed.
The Landing
Everything above is git and holds anywhere. This section is one forge's behaviour, and the commands
are gh. Confirm it on any other before relying on it.
Merging a parent does not move its children. The base branch survives the merge, the child stays aimed at it, and merging the child lands the work on a stale branch instead of the trunk.
Deleting the base does not move them either — it closes them. Seen in practice: a base deleted, and one second later the child closed, still aimed at it. GitHub documents an auto-retarget. Do not spend a pull request finding out when it applies.
So retarget every child first. Delete the parent branch after, or not at all:
gh pr edit <child> --base main
Then read back where it went. A merge reports that it succeeded, never which branch it succeeded into:
gh pr view <child> --json baseRefName,mergedAt
The Anti-Patterns
| Don't | Do | Why |
|---|---|---|
| Merge the parent into the child | Rebase the child onto the parent | A merge puts the parent's diff in the child's review |
| Stack to keep a PR small | Split only what can merge alone | Size is not the virtue. Independence is |
| Add a branch to a waiting stack | Land the bottom first | Every parent rewrite rebases everything above it |