/stack-rebase

name: stack-rebase
description: Cascades a rebase through an entire PR stack after a base PR merges or upstream changes. Use when a stack needs to incorporate new base branch commits.
alwaysApply: false
category: workflow-automation
tags:
- git
- stacked-diffs
- rebase
- pr
- cascade
tools: []
complexity: medium
estimated_tokens: 900
dependencies:
- sanctum:stack-create
- sanctum:stack-push
- sanctum:git-workspace-review

Stack Rebase

Cascade a rebase through an entire PR stack after a base PR merges or the upstream base branch changes.

When To Use

Run `stack-rebase` in any of these situations:

• The first PR in the stack merged into `master`; the

second PR now needs to target `master` directly

• `master` has moved forward and stack branches need to

incorporate the new commits

• A mid-stack PR was revised and descendants need to

pick up the change

When NOT To Use

• The stack has never been published (use `sanctum:stack-push`)
• The stack does not exist yet (use `sanctum:stack-create`)

Prerequisites

• All slice branches exist locally (`git branch --list`)
• Remote is up to date (`git fetch origin`)
• Working tree is clean (`git status`)
• Git 2.38+ for `--update-refs`

Required Progress Tracking

Create progress items before starting:

1. `stack-rebase:fetch-complete` 2. `stack-rebase:trigger-identified` 3. `stack-rebase:rebase-complete` 4. `stack-rebase:conflicts-resolved` 5. `stack-rebase:force-pushed` 6. `stack-rebase:prs-updated`

Step 1: Fetch Remote State (`fetch-complete`)

git fetch origin

If the merged PR's branch still exists on remote, note that GitHub retains the branch after merge. The merged branch itself is no longer a valid stack base.

Step 2: Identify the Trigger (`trigger-identified`)

Determine what changed:

**Case A, Base PR merged into master:** The slice that was the old "root" is now in `master`. All remaining slices need to rebase onto `master`.

# Confirm the merged branch is now in master
git branch -r --merged origin/master | grep "${MERGED_BRANCH}"

**Case B, Master moved forward:** Slices are behind `master` but the stack topology is unchanged. Rebase the root slice onto `master`; `--update-refs` carries all descendants.

**Case C, Mid-stack revision:** A slice was amended. All descendant slices need to rebase onto it.

Step 3: Run the Cascading Rebase (`rebase-complete`)

Case A and B: Rebase root slice onto master

STACK=stack/my-feature
BASE=master

# Check out the root slice
ROOT_SLICE=$(git branch --list "${STACK}/*" \
  | sed 's/^[* ]*//' | sort | head -1)

git checkout "${ROOT_SLICE}"

# Rebase with --update-refs rewrites all stack branches
git rebase --update-refs origin/${BASE}

`--update-refs` scans the reflog and updates every local branch ref that points to a commit being rebased. All slice branches in the stack are rewritten in one pass.

Case C: Rebase from a mid-stack slice

# Check out the first slice BELOW the amended one
CHILD_SLICE=stack/my-feature/add-api  # example

git checkout "${CHILD_SLICE}"
git rebase --update-refs stack/my-feature/add-schema

jj Accelerator (if available)

# jj rebases all descendants automatically on any change
# To rebase the whole stack onto master:
jj rebase -d master \
  -r "ancestors(${STACK}/add-ui) & !ancestors(master)"

Step 4: Resolve Conflicts (`conflicts-resolved`)

If the rebase pauses with conflicts:

# See which file conflicts
git status

# After resolving each file:
git add <resolved-file>
git rebase --continue

Repeat until the rebase completes. If a conflict is too complex, abort and investigate:

git rebase --abort

Then examine the diff between the conflicting commits before retrying.

Step 5: Force-Push Updated Branches (`force-pushed`)

After a successful rebase, push all slice branches. Use `--force-with-lease` to guard against remote changes made since the last fetch:

for branch in $(git branch --list "${STACK}/*" \
    | sed 's/^[* ]*//' | sort); do
  git push --force-with-lease origin "${branch}"
  echo "force-pushed: ${branch}"
done

Never use `--force` (drops the remote-change guard).

jj Accelerator (if available)

jj git push --all --allow-new

Step 6: Update PR Bases (`prs-updated`)

**Case A only**: After the root slice merged and you rebased remaining slices onto `master`, the next PR in the stack now targets the wrong base. Update its base via the GitHub CLI:

NEXT_PR=456   # PR number of the new stack root

gh pr edit "${NEXT_PR}" --base master

For PRs further down the stack, their bases remain the previous slice branch, which `--update-refs` already rewrote; no base edit is needed for them.

Verify the full stack is consistent:

for branch in $(git branch --list "${STACK}/*" \
    | sed 's/^[* ]*//' | sort); do
  pr_num=$(gh pr list --head "${branch}" \
    --json number,baseRefName \
    --jq '.[0] | "#\(.number) base=\(.baseRefName)"')
  echo "${branch}: ${pr_num}"
done

Conflict Prevention Tips

• Keep slices small: the smaller each PR, the less surface

area for conflicts during rebase

• Rebase frequently: rebasing onto a freshly merged master

once a day is cheaper than resolving a week of drift

• Avoid amending commits that are already under review;

prefer a fixup commit and squash at merge time

Notes

• `git rebase --update-refs` requires Git 2.38+; confirm

with `git version` before running

• If `--update-refs` is unavailable, manually check out

and rebase each slice branch in order from root to tip

• After force-pushing, GitHub automatically marks PR

reviews as stale; remind reviewers to re-approve

• The `stack-push` skill documents how to re-post the

stack summary comment after a rebase changes PR SHAs

Exit Criteria

• [ ] All 6 progress items (`stack-rebase:fetch-complete` through

`stack-rebase:prs-updated`) are created before the rebase st