issuelooper: the merger

Check CC_ROLE first (echo "${CC_ROLE:-<unset>}"). If it is not merger,
stop and read ../issuelooper-shared/SKILL.md. Read that file and
.issuelooper/project.md too if you have not: they have the merge gates, the
limits and this repository's commands.

The supervisor merges every pull request GitHub calls mergeable. It starts you
for one that conflicts with main (or whose mergeability GitHub has not
computed for several minutes). Your prompt names the PR ($MERGE_PR), its issue
and its head. You do not merge: the supervisor merges your resolved head on its next
poll, after checking it merged with the current main, and the guard refuses
gh pr merge from you. You write no feature code: you resolve conflicts, nothing
more.

Names below: P=$MERGE_PR, N its issue, WT=/tmp/mrg-$P-wt.

1. Read

gh pr view $P --json number,headRefName,headRefOid,mergeable,body,files
gh pr diff $P
gh issue view $N --json title,labels

If the issue carries hold:monitor or on hold, stop: the guard refuses the
merge, and the hold is not yours to argue.

2. Rebase and resolve

git -C "$SHARED_REPO_PATH" fetch -q origin main "<headRefName>"
git -C "$SHARED_REPO_PATH" worktree add -B "<headRefName>" "$WT" "origin/<headRefName>"
cd "$WT"                        # then the worktree setup from .issuelooper/project.md
git rebase origin/main          # resolve: edit, git add <file>, git rebase --continue

Resolve each conflict so that this PR's change and what landed on main both
survive: imports, adjacent lines, two additions to one list or one CSS block.
Read the PR that landed (git log origin/main -- <file>) when the intent of the
other side is not obvious. Never edit $SHARED_REPO_PATH itself.

Stop and hand back (step 5) when a conflict needs a decision about behavior: the
two sides do different things to the same element and keeping both is not
possible.

3. Sweep, push, review

git push --force-with-lease origin "HEAD:<headRefName>"
python3 .claude/hooks/sweep_locked.py --update-pr $P     # rewrites Sweep SHA and the green line in the body
gh pr view $P --json headRefOid -q .headRefOid            # must equal git rev-parse HEAD
python3 "$SHARED_REPO_PATH/.claude/hooks/review_gate.py" --pr $P

• A red sweep after a clean rebase: hand back, naming the failing test.
• review_gate.py exit 0: go on. Exit 1: it rejected the PR and already handed it
  back (PR comment, issue at stage:triage); stop. Exit 2: run it again.

4. Leave the merge to the supervisor

Stop once the review gate passed, with $N still at stage:pr. Do not merge and
do not change its labels. On its next poll the supervisor merges the new head with
the current main in a worktree, runs the quick check and the merge gates, merges,
and updates the labels; a merge made from an older main broke main more than
once. If the PR conflicts again by then, it starts another merger session.

5. Hand back

Once per PR, and only for a decision about behavior or a red sweep after a clean
rebase:

gh pr comment $P --body "<!-- merger -->
<the hunk or the failing test, and what has to be decided>"
gh issue edit $N --remove-label stage:pr --add-label stage:triage

A worker picks the issue up and updates the same PR.

Finish

cd /, remove $WT (git -C "$SHARED_REPO_PATH" worktree remove --force "$WT"),
and stop.