Merge the winning agent's branch into base, archive losers

/hub:merge — Merge Winner

Merge the best agent's branch into the base branch, archive losing branches via git tags, and clean up worktrees.

Usage

/hub:merge                                       # Merge winner of latest session
/hub:merge 20260317-143022                       # Merge winner of specific session
/hub:merge 20260317-143022 --agent agent-2       # Explicitly choose winner

What It Does

1. Identify Winner

If --agent specified, use that. Otherwise, use the #1 ranked agent from the most recent /hub:eval.

2. Merge Winner

git checkout {base_branch}
git merge --no-ff hub/{session-id}/{winner}/attempt-1 \
  -m "hub: merge {winner} from session {session-id}

Task: {task}
Winner: {winner}
Session: {session-id}"

3. Archive Losers

For each non-winning agent:

# Create archive tag (preserves commits forever)
git tag hub/archive/{session-id}/{agent-id} hub/{session-id}/{agent-id}/attempt-1

# Delete branch ref (commits preserved via tag)
git branch -D hub/{session-id}/{agent-id}/attempt-1

4. Clean Up Worktrees

python {skill_path}/scripts/session_manager.py --cleanup {session-id}

5. Post Merge Summary

Write .agenthub/board/results/merge-summary.md:

---
author: coordinator
timestamp: {now}
channel: results
---

## Merge Summary

- **Session**: {session-id}
- **Winner**: {winner}
- **Merged into**: {base_branch}
- **Archived**: {loser-1}, {loser-2}, ...
- **Worktrees cleaned**: {count}

6. Update State

python {skill_path}/scripts/session_manager.py --update {session-id} --state merged

Safety

• Confirm with user before merging — show the diff summary first
• Never force-push — merge is always --no-ff for clear history
• Archive, don't delete — losing agents' commits are preserved via tags
• Clean worktrees — don't leave orphan directories on disk

After Merge

Tell the user:

• Winner merged into {base_branch}
• Losers archived with tags hub/archive/{session-id}/agent-{N}
• Worktrees cleaned up
• Session state: merged