- graph: enable the dormant Z-buffer. clear() fills depthBuffer with Number.MAX_VALUE each frame; drawGradientTriangle / drawTexturedTriangle now correctly Z-test (lower NDC Z = nearer). Fixes lava-through-ground bleed without painter-order workarounds. Re-enables overlapping 3D forms. - arena: scrap the donut lava — it's a full plane now (Z-buffer handles occlusion). Adds groundSkirt backstop. Adaptive quality tiers (HIGH/MED/LOW) driven by rolling render-time: coarser lava tessellation, static lava (no stripe anim), and dropped body wireframes in LOW. HUD gets PERF label + list of disabled features. Once-per-second diagnostic snapshot + magenta pen crosshair to verify mouse raycast lines up with the hover highlight. Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>