Six failing tests covering all Done-when criteria from #3523:
1. No warning emitted for top-level branching_strategy
2. Value still surfaced via git.branching_strategy after loadConfig
3. Double-emission capped to single-emission per process
4-5. On-disk migration (option 3): write-back + no-clobber guard
6. CJS↔SDK contract: both agree on legacy-shape fixture
Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>
