Merge Use Case

Merge Use Case

Instructions

Land the branch for $ARGUMENTS on main, or stop and report why it cannot land.

The branch prefix follows the work item type: uc/ for UC-XXX, tt/ for TT-XXX, bug/ for BUG-XXX, cr/ for CR-XXX. Every step below writes uc/$ARGUMENTS for readability; use the prefix that matches the ID.

Flags

Use cases are implemented in parallel and merged in series. This skill is the serial part: exactly one invocation may run at a time. It rebases rather than merges, so main keeps the linear history that ${CLAUDE_PLUGIN_ROOT}/shared/tracking/TRACKING.md requires.

When to use

• After /deliver-use-case finishes green and the branch must land on main.
• When a branch that failed the merge gate has been fixed and needs the gate run again.

/deliver-cluster calls this skill itself after every pipeline it starts, so invoke it directly only for a use case delivered on its own.

Prerequisites

• The branch for $ARGUMENTS exists and its worktree holds a green pipeline run
• For a use case, docs/delivery/$ARGUMENTS-iterations.md exists — the pipeline ran

If a use case pipeline has not run, stop and tell the user to run /deliver-use-case $ARGUMENTS first.

Nexa Rules Gate

Read and follow ${CLAUDE_PLUGIN_ROOT}/shared/readiness/NEXA_RULES_GATE.md.

No Worktree Gate

This skill runs in the primary checkout. It reaches into the use case worktree to rebase it, then merges from the primary checkout. It is listed in the Exceptions section of ${CLAUDE_PLUGIN_ROOT}/shared/readiness/WORKTREE_GATE.md.

Merge Lock Gate

Only one merge may run at a time across the whole machine, not just within one session. Several agents may be delivering different use cases or different clusters at once, and each one reaches this skill on its own. Nothing else serializes them, so the lock does.

The lock lives in the shared git directory, which every worktree of the repository resolves to the same path. Ask for it as an absolute path — --git-common-dir alone prints .git, relative to wherever the shell happens to stand, and a lock under the wrong directory locks nothing. Take it before Step 1:

LOCK="$(git rev-parse --path-format=absolute --git-common-dir)/nexa-merge.lock"
mkdir "$LOCK" 2>/dev/null \
  && printf '%s\n%s\n' "$ARGUMENTS" "$(date -u +%FT%TZ)" > "$LOCK/owner" \
  || { echo "LOCKED BY:"; cat "$LOCK/owner"; }

mkdir either creates the directory or fails — there is no window between the check and the create, which is what makes it a lock and not a suggestion.

On failure, stop. Do not merge, do not wait in a loop, and never remove another owner's lock. Report:

MERGE LOCK — HELD

Another merge is in progress: <owner ID>, taken at <timestamp>.

Nothing was merged. The branch for $ARGUMENTS stays in its worktree.
Run /merge-use-case $ARGUMENTS again when that merge finishes, or run
/merge-queue to land every ready branch in order.

Release the lock with rm -rf "$LOCK" on every exit path — after Step 7, after the pull request stop in Step 4 (--review), and equally after a red gate or an unresolvable conflict. A merge that stops without releasing blocks every other agent on the machine.

The one path that keeps the lock is a rejected --ff-only: that returns to Step 1 and rebases again, so the merge is still in progress and the lock still belongs to it.

A lock is stale when its timestamp is older than a full gate run — a build plus the three suites — and no agent reports being mid-merge. Only the user clears a stale lock, with rm -rf "$LOCK".

ponytail: a directory on the local filesystem, so it serializes agents on one machine. Agents on separate machines need a lock on the remote — add one only when that setup is real.

DO NOT

• Run while another /merge-use-case is in progress — the Merge Lock Gate enforces this
• Wait, sleep, or poll for the lock to free up — report and stop
• Remove a lock this invocation did not take
• Merge when the gate is red — there is no "merge anyway" option
• Create a merge commit — main keeps a linear history
• Filter the regression suite with --grep, --grep-invert, or a --project subset
• Force-push main
• Sleep or wait between test retries — diagnose and fix immediately, then re-run

Process

Step 1: Rebase onto main

git fetch origin main
git -C <the UC worktree> rebase origin/main

If the rebase is clean, go to Step 3.

Step 2: Resolve the conflict

Read the work item's specification first, so the resolution follows it rather than a guess about the code:

For each conflicting file:

A clean textual merge is not a correct merge. Two use cases can each add a valid block to the same file and produce a broken result. Step 3 is what proves the resolution, so never skip it after resolving a conflict.

If a conflict cannot be resolved from the specification, stop and report it with both sides quoted. Do not guess.

git -C <the UC worktree> add <resolved files>
git -C <the UC worktree> rebase --continue

ponytail: conflicts are resolved in this context, with no separate merger agent. Promote this step to an isolated agent only if inline resolution proves unreliable in practice.

Step 3: Run the merge gate

The gate runs in the use case worktree, against the rebased tree. This is the check that a sprint used to run once per batch; it now runs once per merge, which is what makes a batch unnecessary.

1. npx next build — must succeed.
2. npx vitest run — must pass.
3. Check whether E2E tests exist (e2e/**/*.spec.ts). If none exist, note "No E2E tests found — regression gate skipped" and go to Step 4.
4. Verify Docker is running, which Testcontainers needs:

   docker info > /dev/null 2>&1
   

   If it is not, ask the user to start Docker or Colima, then re-check.
5. Run the full suite:

   npx playwright test
   

   No filters. Must show 0 failed, 0 skipped, and exit code 0.

On failure, classify each failing test:

• Regression — this use case broke an existing test
• Flaky — the test passes on a re-run with no code change
• Pre-existing — the test already failed on main before this branch

Report:

MERGE GATE — FAILED for $ARGUMENTS

| Test | Classification | Details |
|------|---------------|---------|

The branch stays in its worktree at <path>. Nothing was merged.

Fix the failures there, then run /merge-use-case $ARGUMENTS again.

Allow up to 3 re-runs for tests classified as flaky. A regression is never waived — fix it and re-run the gate. If the failure is pre-existing on main, report it as a separate bug with /report-bug and stop; a broken main is not this use case's problem to hide.

Step 4: Land the branch

Default — merge without review:

git checkout main
git merge --ff-only uc/$ARGUMENTS
git push origin main

The rebase in Step 1 guarantees the fast-forward. If --ff-only is rejected, main moved while the gate ran — return to Step 1 and repeat.

With --review — stop at the pull request:

git push -u origin uc/$ARGUMENTS
gh pr create --base main --head uc/$ARGUMENTS \
  --title "$ARGUMENTS: <use case name>" \
  --body "<the delivery summary, plus a link to docs/use_cases/$ARGUMENTS.md>"

Then release the lock — the gate is finished and nothing else in this run touches main:

rm -rf "$(git rev-parse --path-format=absolute --git-common-dir)/nexa-merge.lock"

Then stop. Do not merge, and do not remove the worktree — the reviewer may ask for changes.

Say what is now blocked. The pull request path does not set the specification to Done on main, so every use case that depends on this one stays blocked until the pull request lands. Report:

$ARGUMENTS is awaiting review: <pull request URL>

Nothing was merged. Worktree kept at <path>. Merge lock released.
Blocked until this lands: <dependent work item IDs, or "none">

When the pull request is merged, run:
  /merge-use-case $ARGUMENTS --after-review

Step 4b: After the review lands (--after-review)

Run this once the pull request has been merged on GitHub — by a human, or with gh pr merge <number> --rebase --delete-branch=false. It performs only the bookkeeping the merge path would have done:

git checkout main && git pull --ff-only origin main

Confirm the branch's commits are on main (git branch --merged main lists it). Then continue at Step 5 — close the issue, remove the worktree, delete the branch, and report. Without this step the worktree and the branch leak and every dependent use case stays blocked forever.

Step 5: Close the tracking issue

Follow the After Implementation steps in ${CLAUDE_PLUGIN_ROOT}/shared/tracking/TRACKING.md. That file owns the whole issue lifecycle; do not repeat its steps here.

Step 6: Remove the worktree

git worktree remove ../$(basename "$PWD")-$ARGUMENTS
git branch -d uc/$ARGUMENTS

git branch -d refuses to delete an unmerged branch. That is the safety check — if it refuses, the merge did not happen and something above went wrong. Never force it with -D.

git worktree remove refuses when the directory holds modified or untracked files. The gate just ran a build and three test suites in there, so playwright-report/, test-results/, and reports/mutation/ are the usual cause. Confirm the branch is merged (git branch --merged main lists it), then repeat with --force, and add those paths to the project's .gitignore so it does not recur. Do not skip this step — a leaked worktree keeps its branch alive and makes Verification 2 and 3 fail on a merge that actually succeeded.

Step 7: Release the lock and report

rm -rf "$(git rev-parse --path-format=absolute --git-common-dir)/nexa-merge.lock"

## Merged: $ARGUMENTS — <use case name>

| Gate                | Result |
|---------------------|--------|
| Rebase onto main    | clean / N conflicts resolved |
| Build               | pass   |
| Unit tests          | pass   |
| E2E regression      | N passed, 0 failed, 0 skipped |

Merged to main as <short SHA>. Worktree removed. Merge lock released.

Verification

0. <git-common-dir>/nexa-merge.lock does not exist — the lock was released, whatever the outcome.
1. git log --graph --oneline main | head shows no merge commit.
2. git worktree list no longer lists the use case worktree.
3. git branch --list "*/$ARGUMENTS" returns nothing.
4. The GitHub issue for $ARGUMENTS is closed.
5. The work item's specification has the status its type ends at — Done for a use case, a technical task, and a change request; Fixed for a bug. See ${CLAUDE_PLUGIN_ROOT}/shared/tracking/TRACKING.md, which owns the status transitions.