Three architecture documents from Sprint 6 design work: - z-layer-gap-analysis.md: full three-scope rendering pipeline with reserved z-ranges, airborne treatment, cross-floor VFX, liquid depth - fog-shader-spec.md: 5-layer fog shader architecture (D-059) - flying-taxi-analysis.md: validates z-layer architecture supports flight scenarios with LOD tiers and performance budget Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>