Acceptance checklist

Work through this before you submit. Everything has to pass.

Interaction

• OrbitControls damping is on; zoom distance and pitch are both clamped
• Opening shot is around 3.2×R, tilted slightly down, whole model on one screen
• The wheel inside the 3D area never scrolls or zooms the page
• Frame rate holds while a slider is dragged continuously (geometry rebuilds are debounced)
• Changing any parameter leaves the camera where it was and does not interrupt motion
• Drag springs back on release; idle has a slight float; prefers-reduced-motion disables all of it
• The 3D stage sets user-select: none — dragging never selects page text

Correctness

• 3D geometry, the 2D canvas and the exported file all come from one IR (change any parameter and all three follow)
• The Y-down → Y-up flip happens once on the content group — not per mesh, not on the geometry. No mirrored text, no holes on the wrong side, no inside-out faces
• Every panel parameter has a visible effect in the 3D view, or is hidden for that mode with an explanation — a parameter that is visible but does nothing is not acceptable

Performance and stability

• setPixelRatio is clamped (DPR ≤ 2)
• Five minutes of continuous parameter changes with flat GPU and JS memory (everything is disposed)
• Hide the tab and come back: the view is intact, not blank, nothing lost
• Mounting at 0×0 still initialises correctly once a real size arrives
• A container resize updates camera.aspect, updateProjectionMatrix() and setSize() together — the view refits without stretching

Render quality

• Environment lighting is configured (RoomEnvironment or HDRI) with a directional light on top — not bare AmbientLight
• ACES tone mapping is on
• The environment map and any shared texture are built once and disposed on unmount only — not regenerated or disposed per rebuild
• Top and side materials are separate groups, sides a shade darker
• No three.js deprecation warnings in the browser console