Putting Plan Execution on Top of the Review Loop: Building sparring 0.4.0

As sparring went from v0.2.0 to v0.4.0, it gained a risk-triggered final sweep and safe skips (Phase 4), and /spar-weighin (Phase 8): an orchestrator that runs a checkbox plan through the review loop task by task. This post covers the new features and the issues I hit while building them — an unreliable Stop hook ordering, a critical defect the cross-model review caught, and a worktree isolation bug — along with how each was resolved.