FillExtents vertical copy distance was not clamped, allowing rows to be placed overlapping each other when slide calculations returned large values. Clamp to pairHeight + partSpacing minimum, matching FillLinear. Also add FillStrategyRegistry.SetEnabled() to restrict which strategies run — useful for isolating individual strategies during troubleshooting. Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>