- Guard max_leaf_nodes < 2 (sklearn requires ≥ 2 or None)
- Update expansion benchmark table in README with v2.12.1 results
- FastHVRT-var achieves best TSTR Δ (−0.004) on multimodal expansion
- All 243 tests pass

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>