Boundary test that fails on bit-pick-first or bit-pick-max regressions of the open_horizon_masks averaging in stop_check_isv. Per-horizon pnl_ema_loss values (2, 4, 3, 3, 3) yield mean=3.0 across the 0x1F mask; snapshots placed relative to vwap_entry for ask-spread safety. Tests Δ_entry=2.5 (no-fire) and Δ_entry=4.5 (fire). Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>