- Reproduce historical results: ca933e4 code achieves 43.20% annual return
- Attribution analysis: crash filter simplification (+4pp) + data extension (+2pp)
- Start year traversal: 2020-2025, all years show 34-57% annual return
- Compare ca933e4 vs HEAD (cabfee2) across different start years
- Add test_start_year_analysis.py for reproducibility
