M15 trail arm 0.70 (validated grid) + backtest/live parity hardening

Parity: replay now applies the live _apply_regime_filter_live method
under the live guard (function-identity, default-off); unregistered-pair
fallback applies the config.json overlay; parity sweep gains direct
ATR/vol-regime assertions; regime-filter semantics test added.

Trail campaign: --trail-arm/--trail-dist research flags; 30-cell grid on
5yr M15 refuted the earlier-arm hypothesis and found the 0.70-0.80 arm
plateau. Shipped M15-only trail_arm_r=0.70 (factory override):
+210.7R PF 1.35 WR 57.8% vs +175.7R PF 1.30 WR 53.9% baseline; both
halves and 2024-06->2025-03 OOS better (+57.4 vs +45.4); 5yr max-DD
clause (33.9R vs 29.1R) explicitly waived by owner. M5 unchanged.
Factory replay reproduces the grid cell trade-for-trade; 201/201 tests.

Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01VPNF37MP9Kuv62B1VBrZ1b

.gitignore

@@ -25,6 +25,7 @@ Thumbs.db
 # Backtesting data (keep scripts, ignore generated files)
 backtest/cache/
 backtest/*.csv
+backtest/trailgrid/
 backtest/__pycache__/
 .env.*
 logs/