Visual: replace spike clumps with luminous meadow grass

[ael-dev3]

Summary

This draft PR replaces the old sparse black spike clumps with bright, distributed meadow grass. It stays presentation-only and keeps the existing camera-local cache, shared ambient scheduler, interaction uniforms, and raycast/lifecycle boundaries intact.

Base and scope

• Base: f23643c0d07e91847cadd5445a294d965ad76e1c (current main, Alpha 0.3.11)
• Head: fc95959d3c2128c267e535a6e6cffec5aaa692ff
• No gameplay, terrain membership, passability, resource, route, economy, or SpacetimeDB changes.
• No deployment or merge performed.

Defect diagnosis

The previous 5/4/3 crossed-ribbon crowns shared one local root, used tall/narrow biome ranges, multiplied muted tints by a dark material base, and scaled complete geometry to zero at the active-window edge. The result read as sparse black “nose hair” instead of ground cover.

Geometry and hard budgets

Quality	Blades/patch	Variants	Max patches	Triangles/patch	Max triangles	Draw calls
High	9	3	7,000	27	189,000	3
Balanced	7	2	4,000	21	84,000	2
Reduced	5	1	1,200	15	18,000	1

Patch roots are deterministic, distributed in the 0.08–0.46 local disk, planted away from the exact origin, and use independent blade yaw, lean, phase, stiffness, and height.

Density and colour

• Meadow/Lowland candidate and retention policy remains deterministic but uses broader patch radii and shorter blades.
• Authored palettes use the requested sRGB hex values and are converted once through THREE.Color into linear storage.
• Root/tip lift is bounded in the shader. Grass stays brighter than terrain while Heath/Ridge/Ancient Stone remain restrained.
• Active-window edges fade fragment coverage through alpha-hash inputs; X/Z footprint is not collapsed.

Material and wind contract

• MeshStandardMaterial, opaque depth-writing material, DoubleSide, alpha hash, optional alpha-to-coverage only when the renderer reports MSAA.
• Coverage is interior-heavy, fades at blade edges and tips, and preserves fog/tone mapping.
• Roots stay planted. Upper vertices combine shared world wind, patch phase, blade phase, stiffness, gust, and reduced-motion caps.
• No new RAF, per-frame matrix writes, or per-instance animation loop.

Validation

• tsc -b
• vite build
• 9 focused Vitest files, 71 tests passed (geometry, palette/material, layer, active window, Genesis determinism, scene cleanup, and quality budgets).
• Fixed-camera rendered before/after capture is intentionally not committed; the existing rendered harness remains the follow-up visual QA surface. No private desktop paths are included.

Residual risks

Alpha-hash grain at low resolution, MSAA-dependent alpha coverage, extra variant draw calls, mobile thermal cost, Three r185 shader-hook drift, and no physical grass interaction remain explicit risks.

[ael-dev3]

Superseded by merged PR #72. The grass work was integrated with deterministic visual contracts and a constrained-WebGL repair that reduces active vertex attributes from 18 to 13.