fork-upstream-sync

name	fork-upstream-sync
description	Sync a GitHub fork with upstream while keeping unmerged feature branches and open PRs mergeable. Use for rebase on upstream, PR conflicts, integration main. Don't use for git init, releases, or non-fork repos.
license	MIT
effort	medium
metadata	{"version":"1.3.2","author":"Luong NGUYEN <[e-mail]>"}

Fork Upstream Sync

Integration main means fork main = upstream/main plus your unmerged commits in linear history (not a merge commit that duplicates feature work).

Prerequisites

Before selecting a path, validate all requirements:

• Tools: require Git 2.30+; require gh only for PR-state checks.
• Access: confirm authenticated fetch and push access to origin, plus fetch access to upstream.
• State: check that the working tree is clean or stashable and that the target branches are not checked out in another worktree.
• Recovery: record the current branch and SHA. If fetch, stash, rebase, reset, or push fails, stop at that command; never continue with stale assumptions.

Branch selector

Pick one path per user request:

Path	When
A — Bootstrap	No upstream remote yet, or first-time fork sync
B — PR branch	Open PR is CONFLICTING or DIRTY; rebase feature branch on upstream/main
C — Integration main	Fork main should match upstream plus same tip as feature branch
D — Post-merge	Upstream merged your PR; drop duplicate commits on fork main

Paths B then C is the usual full sync (PR mergeable, fork main carries your WIP).

Repo sync before edits (mandatory)

Before any rebase, reset, or force push:

git fetch upstream
git fetch origin

If the working tree is dirty:

git stash push -u -m "pre-sync: $(git rev-parse --abbrev-ref HEAD)"
# ...run the fetch/rebase/reset steps for the chosen path...
git stash pop

On git stash pop conflict, stop — the stash is preserved (git stash list); resolve manually before continuing.

If upstream is missing, origin is missing, or the user has not said which upstream org/repo to use, stop and ask. Never force-push main without --force-with-lease.

Step completion reports

After each major phase, emit a short report with checks for upstream remote, commits behind upstream, PR mergeable status, conflicts resolved, and whether integration main matches the feature branch tip. End with Result PASS, FAIL, or PARTIAL.

---

Path A — Bootstrap upstream remote

1. Confirm parent repo (for example gh repo view --json parent,isFork).
2. Add remote if absent: git remote add upstream [e-mail]:ORG/REPO.git, then git fetch upstream.

Done when: git rev-parse upstream/main succeeds and git remote -v lists upstream.

---

Path B — Rebase feature branch on upstream

1. Identify PR head branch and upstream base (main).
2. git checkout <feature-branch> then git rebase upstream/main.
3. On each conflict, resolve files. When upstream and your feature both added valid code, keep both (union), not either/or. If a conflict can't be confidently resolved, git rebase --abort and stop to ask the user rather than guessing.
4. git add resolved files, then GIT_EDITOR=true git rebase --continue.
5. For locale JSON conflicts, keep the rebased side then run the repo catalog fix if documented (for example pnpm run sync:localization-catalog --fix).
6. git push origin <feature-branch> --force-with-lease.
7. Verify with gh pr view <n> --repo ORG/REPO --json mergeable,mergeStateStatus (expect MERGEABLE; CI may lag).

Done when: rebase completes, no conflict markers in tree, PR is MERGEABLE or user accepts waiting on CI.

---

Path C — Rebuild fork integration main

After Path B:

git checkout main
git reset --hard upstream/main
git merge --ff-only <feature-branch> && git push origin main --force-with-lease

If --ff-only fails, main is already reset to bare upstream/main — do not push. The feature branch is behind the new upstream/main; re-run Path B to rebase it, then retry this merge. Pushing here without the fast-forward would force-publish plain upstream/main, silently dropping your integration WIP from origin/main.

Done when: upstream/main is ancestor of main, main SHA equals feature branch SHA, and ahead count matches your feature commits.

---

Path D — Post-merge cleanup

When upstream main already contains your merged PR:

git fetch upstream
git checkout main
git reset --hard upstream/main
git push origin main --force-with-lease

Done when: main SHA equals upstream/main SHA.

---

Verify with the command reference

Protect the context budget: read references/command-checks.md only when executing or diagnosing a path. See that reference for the routine command sequence and exact SHA, ancestry, ahead-count, and clean-tree checks.

What not to do

• Do not merge upstream/main into fork main with a merge commit while also keeping a parallel rebased feature branch.
• Do not force-push without --force-with-lease.
• Do not treat origin as upstream; origin is your fork, upstream is the parent.

Acceptance criteria

Verify the selected path before reporting success:

• Required remotes resolve and the working tree has no unresolved conflicts.
• The expected branch ancestry or equality check for the selected path passes.
• Every push used --force-with-lease; no destructive push targeted the wrong branch.
• For Path B, the PR response is MERGEABLE, or CI delay is explicitly reported as partial.

Run:

git log --oneline -1 upstream/main main <feature-branch>
git rev-list --count upstream/main..main
git merge-base --is-ancestor upstream/main main

Expected output: the log identifies the intended tips, the ahead count equals the retained feature commits, and the ancestry command exits 0. For Paths C and D, also assert the exact SHA equality required by that path.

Edge cases

• Renamed default branch: discover it with gh repo view --json defaultBranchRef; do not assume main.
• Protected fork branch: if GitHub rejects a lease-protected push, stop and report the protection rule; do not weaken it.
• Deleted PR branch: recreate only from a verified local or remote SHA after user confirmation.
• Upstream rewrote history: fetch, compare old and new tips, and ask before rebasing or resetting across the rewrite.