msd-core/docs/adr/230-introduce-next-integration-branch.md

Introduce next as a long-lived integration branch

• Status: Proposed
• Date: 2026-05-23

Filename note. This ADR uses the placeholder (now resolved to 230) per CONTRIBUTING.md §Proposing an ADR. Before merging, open a chore: issue, replace XXXX with the assigned issue number, and rename the file accordingly.

Context

Today every contributor branch — feat/, fix/, chore/, docs/, refactor/, test/, perf/, ci/, revert/ — is cut from main and PR'd back to main. Release branches (release/X.Y.0) and hotfix branches (hotfix/X.Y.Z) are also cut from main. As a result:

1. main moves on every merge. With ~315 unreleased changesets queued and multiple PRs in flight at any time, main advances multiple times a day.
2. GitHub branch protection on main requires "branches up to date before merging" (the dominant pattern across mature OSS projects with linear history). Every time another PR lands, every in-flight PR must rebase before its own merge button enables.
3. release/X.Y.0 accumulates RC-cycle fixes that drift from main. When finalize opens the merge-back PR, the diff is large and contributors who PR'd to release/* can't be sure their fix is also queued for the next minor.
4. hotfix.yml cherry-picks fix:/chore: commits from main since the prior tag. This works today only because every fix lands on main. The pattern is fragile — any deviation (e.g. fix landing on release/*) is invisible to the picker. v1.42.3 (#3621) shipped a half-state for exactly this class of reason.

The maintainer's stated pain: "every update doesn't mean the next pr needs a rebase" — i.e. the rebase treadmill from (2), driven by (1).

Decision

Introduce next as a long-lived integration branch.

• All work that today targets main instead targets next, with the sole exceptions of release/X.Y.0 and hotfix/X.Y.Z branches, which still merge to main.
• next is always at-or-ahead of main. Any push to main (release or hotfix merge) triggers an automated back-merge PR main → next to keep next aligned.
• Branch protection rules differ:
  • main — strict: 2 reviewer approvals, all CI green, "require branches up to date" ON, signed commits, restrict push to maintainers via PR only.
  • next — loose: 1 reviewer approval, all CI green, "require branches up to date" OFF, auto-delete source branches.
• Default branch (in repo Settings) becomes next. gh pr create and the GitHub web UI then default new PRs to the correct target without a flag.

Where each branch type goes

Branch prefix	Today's target	New target	Rationale
feat/	main	next	Features ship in minor releases
fix/	main	next	Regular fixes ship in minor (or get cherry-picked by hotfix.yml)
chore/, docs/, refactor/, test/, perf/, ci/, revert/	main	next	All same-flow as fixes
fix/critical-*	main	main	Production-down only, auto-back-merges to next
release/X.Y.0	main	main (cut from next)	Promoted to production on finalize
hotfix/X.Y.Z	main	main (cut from prior tag, cherry-picks from next)	Patch releases

Mechanical changes summary

Component	Change
release.yml (create)	Branch from next, not main
release.yml (finalize)	Open merge-back PR to both main and next (was just main)
hotfix.yml (cherry-pick step)	Cherry-pick from origin/next, not origin/main
hotfix.yml (finalize)	Open merge-back PRs to both main and next (was just main)
branch-naming.yml	Add next to alwaysValid list
auto-branch.yml	Branch from next HEAD instead of main HEAD for issue-labeled branches
New pr-target-validator.yml	Block PRs targeting main from branches that aren't release/*, hotfix/*, or fix/critical-*
New auto-backmerge.yml	On push to main, open main → next PR
Repo settings	Default branch = next; squash-merge only on next; merge-commit on main (preserve tag context)
scripts/setup-branch-protection.sh	New: idempotent script to apply both branch protection rule sets via gh api

Consequences

Positive

• Rebase treadmill ends. PRs targeting next are not gated on "up-to-date before merge". Concurrent PRs to next merge in any order as long as they don't conflict on the same lines.
• main becomes a stable reference. It changes only on release/hotfix merges — a handful of times per week, not multiple times per day. CI on main runs less; downstream consumers (linked CI, npm tag watchers) see fewer transient states.
• Hotfix cherry-pick base is unambiguous. All fix:/chore: commits candidate for a hotfix live on next. The cherry-pick filter (today hardcoded against origin/main) becomes correct-by-construction once retargeted to origin/next.
• RC-only fixes flow back to next automatically. Today a fix that lands on release/1.28.0 to unblock RC2 only makes it to next-equivalent (i.e. main) when finalize back-merges. Under the new model finalize back-merges to both main and next, so an RC fix is never accidentally dropped from the next minor.
• Default branch switch is one click. Cost is low; setting takes effect for every new PR and clone immediately.

Negative

• One more concept to teach contributors. Mitigated by docs/branching.md
  • CONTRIBUTING update + PR-target validator that says "retarget to next" with a one-line fix instruction.
• Hotfix and release workflows need updates. Patches are inlined below. Both are reversible — if a patch causes pain, revert and re-target the workflows back to main. No on-disk state migration required.
• The auto-backmerge PR is a new background-noise source. It opens silently after each release/hotfix push to main. Mitigated by labeling the PR automation and auto-merging if CI passes (configurable in auto-backmerge.yml).
• Existing 315-changeset queue. Doesn't strictly block this change but the next release will be a large one. Recommend cutting 1.28.0 from main (current behavior, last time) before flipping the default branch to next — see "Migration" below.

Risks not worth the trade-off

We considered and rejected:

• develop instead of next. The git-flow nomenclature is established but the gitflow model itself is heavier than this project needs (no long-lived release/* branches per-major, no support/* for old majors). next matches the existing npm dist-tag (@next) and is the convention for Angular, Next.js, React Native, and others. Use the name that already appears in VERSIONING.md.
• Merge queue. GitHub's merge queue (GA in 2023) addresses the same pain by serializing merges and rebasing+testing automatically. Rejected because (a) it doesn't address the parallel work-stream separation that a next branch gives, (b) it still requires "branches up to date" which we want to relax, and (c) the maintainer is a git beginner and merge queue's failure modes (split commits, requeued PRs) are harder to debug than a conventional model.
• Pure trunk-based with feature flags. Rejected because the project publishes to npm and doesn't have a runtime feature-flag system. Feature flags would be a larger separate investment.

Migration

This is a phase-gated rollout. Each phase is reversible.

Phase 0 — Decide

1. Open a chore: issue: "Introduce next integration branch". Get the issue number. Rename this ADR file from XXXX- to <issue#>-.
2. Review this ADR. Decide on the merge-commit-vs-squash policy for next (recommended: squash) and for main (recommended: merge commit on release back-merges, to preserve the tag-commit relationship).

Phase 1 — Additive infrastructure (no behavior change)

The following land on main (current model, one last time) before flipping:

• docs/branching.md (new)
• docs/adr/<issue#>-introduce-next-integration-branch.md (this file)
• scripts/setup-branch-protection.sh (new)
• .github/workflows/auto-backmerge.yml (new, disabled with if: false until phase 2)
• .github/workflows/pr-target-validator.yml (new, in "warning only" mode)
• .github/workflows/branch-naming.yml (update: add next to alwaysValid)
• CONTRIBUTING.md update: "Where do I open my PR?" section

Phase 2 — Flip

When the next release is ready to start its RC cycle:

1. Cut the current planned release (e.g. 1.28.0) using release.yml as today — this drains the 315-changeset queue from main cleanly.
2. After v1.28.0 finalizes and back-merges to main, run:

   git checkout main && git pull --ff-only
   git checkout -b next && git push -u origin next
   

3. Apply branch protection: bash scripts/setup-branch-protection.sh.
4. Settings → Branches → change default branch to next.
5. Re-enable auto-backmerge.yml (remove the if: false).
6. Flip pr-target-validator.yml from warning-only to enforcing.

Phase 3 — Retarget release/hotfix workflows

Apply these patches once next is established and the team has run at least one feature PR through it.

release.yml — branch from next (create step):

@@ create:
       - name: Create release branch
         env:
           BRANCH: ${{ needs.validate-version.outputs.branch }}
           VERSION: ${{ inputs.version }}
           IS_MAJOR: ${{ needs.validate-version.outputs.is_major }}
         run: |
+          git fetch origin next:next || git fetch origin main:main
-          git checkout -b "$BRANCH"
+          git checkout -b "$BRANCH" next 2>/dev/null || git checkout -b "$BRANCH" main

The || main fallback is for the transition window where next may not yet exist. After Phase 2 the fallback can be removed.

release.yml — back-merge to both branches (finalize step):

@@ Create PR to merge release back to main
       - name: Create PR to merge release back to main
         ...
+      - name: Create PR to merge release back to next
+        if: ${{ !inputs.dry_run }}
+        continue-on-error: true
+        env:
+          GH_TOKEN: ${{ github.token }}
+          BRANCH: ${{ needs.validate-version.outputs.branch }}
+          VERSION: ${{ inputs.version }}
+        run: |
+          EXISTING_PR=$(gh pr list --base next --head "$BRANCH" --state open --json number --jq '.[0].number' 2>/dev/null || echo "")
+          if [ -n "$EXISTING_PR" ]; then
+            gh pr edit "$EXISTING_PR" \
+              --title "chore: merge release v${VERSION} to next" \
+              --body "Merge release branch back to next after v${VERSION} stable release (picks up RC-only fixes)." \
+              || echo "::warning::Could not update next merge-back PR. Open it manually."
+          else
+            gh pr create \
+              --base next \
+              --head "$BRANCH" \
+              --title "chore: merge release v${VERSION} to next" \
+              --body "Merge release branch back to next after v${VERSION} stable release (picks up RC-only fixes)." \
+              || echo "::warning::Could not create next merge-back PR. Open it manually."
+          fi

hotfix.yml — cherry-pick from next (with main fallback):

@@ Cherry-pick fix/chore commits from origin/main since base tag
-      - name: Cherry-pick fix/chore commits from origin/main since base tag
+      - name: Cherry-pick fix/chore commits from origin/next since base tag
         ...
         run: |
           set -euo pipefail
-          git fetch origin main:refs/remotes/origin/main
+          # Prefer next; fall back to main during the transition window or
+          # for production-down emergencies that landed directly on main.
+          if git ls-remote --exit-code origin next >/dev/null 2>&1; then
+            git fetch origin next:refs/remotes/origin/next
+            SOURCE="origin/next"
+          else
+            git fetch origin main:refs/remotes/origin/main
+            SOURCE="origin/main"
+          fi

-          CANDIDATES=$(git cherry "$BASE_TAG" origin/main | awk '/^\+ / {print $2}')
+          CANDIDATES=$(git cherry "$BASE_TAG" "$SOURCE" | awk '/^\+ / {print $2}')
...
-          ORDERED=$(git log --reverse --format='%H' "$BASE_TAG..origin/main" \
+          ORDERED=$(git log --reverse --format='%H' "$BASE_TAG..$SOURCE" \
             | grep -F -f <(echo "$CANDIDATES") || true)

hotfix.yml — back-merge to both branches (finalize step):

@@ Create PR to merge hotfix back to main
       - name: Create PR to merge hotfix back to main
         ...
+      - name: Create PR to merge hotfix back to next
+        if: ${{ !inputs.dry_run }}
+        env:
+          GH_TOKEN: ${{ github.token }}
+          BRANCH: ${{ needs.validate-version.outputs.branch }}
+          VERSION: ${{ inputs.version }}
+        run: |
+          EXISTING_PR=$(gh pr list --base next --head "$BRANCH" --state open --json number --jq '.[0].number')
+          if [ -n "$EXISTING_PR" ]; then
+            gh pr edit "$EXISTING_PR" \
+              --title "chore: merge hotfix v${VERSION} back to next" \
+              --body "Merge hotfix changes back to next after v${VERSION} release."
+          else
+            gh pr create \
+              --base next \
+              --head "$BRANCH" \
+              --title "chore: merge hotfix v${VERSION} back to next" \
+              --body "Merge hotfix changes back to next after v${VERSION} release."
+          fi

auto-branch.yml — branch from next:

-            // Create branch from main HEAD
-            const mainRef = await github.rest.git.getRef({
+            // Create branch from next HEAD (fall back to main if next missing)
+            let baseRef;
+            try {
+              baseRef = await github.rest.git.getRef({
                 owner: context.repo.owner,
                 repo: context.repo.repo,
-              ref: 'heads/main',
-            });
+                ref: 'heads/next',
+              });
+            } catch (e) {
+              if (e.status !== 404) throw e;
+              baseRef = await github.rest.git.getRef({
+                owner: context.repo.owner,
+                repo: context.repo.repo,
+                ref: 'heads/main',
+              });
+            }

             await github.rest.git.createRef({
               owner: context.repo.owner,
               repo: context.repo.repo,
               ref: `refs/heads/${branch}`,
-              sha: mainRef.data.object.sha,
+              sha: baseRef.data.object.sha,
             });

Phase 4 — Cleanup

After 2-3 successful releases under the new model:

• Remove the || main fallbacks from release.yml and hotfix.yml.
• Remove develop from branch-naming.yml alwaysValid (it was vestigial; the project never used it).
• Drop warning-only mode from pr-target-validator.yml.

References

• docs/branching.md — contributor-facing how-to-use-it guide
• VERSIONING.md — semver tiers and npm dist-tag mapping
• .github/workflows/release.yml, .github/workflows/hotfix.yml — release/hotfix automation that this ADR adjusts
• scripts/setup-branch-protection.sh — bootstrap script for branch protection rules
• Angular branching model — closest analogue (main + <version>-next)
• Next.js release flow — uses canary as the integration branch with the same shape