Even out Studio and share lighting

[w1ne]

Why

Production share paints (develop after #872) are still the pre-AgX rig. The AgX / dim-light / room-environment change in a272125 was reverted inside #872 and left on feat/viewer-lighting-agx. What app.kernelcad.com actually ships, confirmed in assets/index-BP6uzJra.js:

• NeutralToneMapping, exposure 1
• ambient 0.5, key 0.7 at [10, 20, 10], fill 0.3 at [-5, -10, -5]
• no RoomEnvironment on the Studio canvas

The scene is Z-up, so that key is a side light (its largest component is +Y). Metalness-1 faces have nothing to reflect, so they go black except for a white specular spike. Dark dielectrics fall under luma 20. Brushed aluminium (anisotropy: 0.8 on the published T-slot) has no vertex tangents, and that degenerate frame paints whole faces black and white.

The demo player keeps its own Neutral rig at exposure 1 and room intensity 0.3. This PR does not touch it.

New numbers

	Before (prod)	After
Tone mapping	Neutral	AgX
Exposure	1	1
Environment	none	RoomEnvironment 0.62, rotated +90° about X so the room ceiling is +Z
Fill	ambient 0.5	hemisphere sky 0xf7f8fa, ground 0xd2d6db, intensity 1.45, from [0, 0, 1]
Key	[10, 20, 10] @ 0.7	[10, -8, 22] @ 0.34
Fill light	[-5, -10, -5] @ 0.3	[-12, 10, 16] @ 0.26
Anisotropy	authored, including 0.8 with no map	0 unless an anisotropy map is set (metalness and roughness stay authored)

Hemisphere intensity is above 1 because three.js divides indirect light by π; the two directionals are the form. Both are overhead (+Z is the largest component) and within 1.3× of each other, so the side turned away from the key stays a shade.

AgX stays. Neutral plus the old hot key is what clipped light faces. ACES is the tone map that crushes saturated CAD hues; it was not brought back.

White-clip check

Headless Chromium (SwiftShader), the same three.js lights, AgX, and RoomEnvironment as the viewer, on the published CDN meshes. Model pixels are everything that is not the #202126 stage. Blown = luma > 245, dark = luma < 20.

T-slot OGm0lP_B v1 (aluminium-brushed, metalness 1, anisotropy 0.8):

• prod: 72% dark, 11% blown, max luma 252
• new lights with anisotropy left on: 12% blown, max luma 254 (the white-clip failure)
• shipped (anisotropy cleared, no map): 0% dark, 0% blown, max luma 197, every model pixel in the mid band

4DOF arm DNSlHVFO v1 (mostly #243140 dielectric, roughness 0.55):

• prod: mean luma 17, 80% dark, max 218
• shipped: mean luma 136, 0% dark, 0% blown, max luma 236, 98% mid

Ortho face centers on finish swatches under the shipped rig (aluminium, brushed, stainless, nylon, delrin, white #f4f4f4, ABS, servo blue): no face mean above 235, blown fraction 0. White #f4f4f4 reads 184–216. Pinning envMap at intensity 0.62 and the same rotation matches scene.environment exactly.

OGm0lP_B — T-slot frame corner

Before (production rig):

OGm0lP_B T-slot before, production rig

After (shipped rig):

OGm0lP_B T-slot after, shipped rig

DNSlHVFO — 4DOF arm

Before (production rig):

DNSlHVFO 4DOF arm before, production rig

After (shipped rig):

DNSlHVFO 4DOF arm after, shipped rig

These are the stored meshes rendered with the viewer’s light constants, not a screenshot of the Studio chrome. The disconnected arm geometry is unchanged.

Tests

• Viewer.test.tsx locks AgX and exposure 1
• viewerLighting.test.ts locks the intensities, the overhead key, and the key/fill ratio
• roomEnvironment.test.ts locks per-scene IBL, intensity 0.62, and the +Z rotation, including that one canvas cannot receive another’s texture
• buildShapeMaterial.test.ts locks anisotropy 0 without a map, and keeps 0.8 when a map is set

Do not merge until the share-page look is approved.

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