Schema for what the merger should do in other worktrees still checked out
on the integration branch when it advances the branch ref. Modes:
off — legacy (user pulls manually)
ff-only — fast-forward only when other worktree is clean
stash-and-ff — Smart Pull pipeline (default)
Threads through DEFAULT_PROJECT_SETTINGS, PROJECT_SETTINGS_KEYS (auto via
Object.keys), the docs settings table, and parity + persistence tests.
Merger consumption lands in the follow-up engine change.
Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>
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