stats.sx reports hit-ratio, cost-weighted work-recomputed/work-saved,
savings-ratio, and exec-summary over an execution record. Verifies cold (0
saved), warm (all saved), and incremental (saved = unchanged, ran = dirty
closure). stats 12/12, total 144/144.
Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>
