ogpu: Skill for Claude Code

Scaffold a simple WGSL shader

Generate a minimal, correct WGSL file (plus optional JS wiring) for a mesh rendered through Shader + Mesh. The base shader is deliberately bare — vs/fs reading the engine's camera.*/object.* and a fragment that outputs the normal mapped to 0..1. No custom uniforms, no textures: those are modifications you layer on top after generating, per the task. The reference shape is examples/hellowebgpu/cube.wgsl (same conventions).

Conventions that are NOT optional

These come from the reflection in Shader — get one wrong and the draw silently shades garbage or fails construction:

• Line 1 is // validate-prepend: <relative path to src/core/engine.wgsl> so validate-shaders can compile the file (the script computes the path).
• Do NOT declare matrices/time/viewport in a Uniforms struct. Shader appends the engine block (src/core/engine.wgsl): @group(1) camera (projectionMatrix, viewMatrix, cameraPosition, cameraQuaternion, viewport; one slot per render()), @group(1) object (modelMatrix, normalMatrix (mat3x3f), objectMatrix (inverse model); one fixed slot per mesh) and @group(3) time (time, delta, seconds). Read camera.* / object.* / time.*; don't declare your own module-scope time. There is no stored modelView; per vertex write camera.projectionMatrix * (camera.viewMatrix * (object.modelMatrix * p)) (WGSL * is left-associative, so P * V * M * p does mat-mat products per vertex). modelViewMatrix() returns the matrix where code needs it. Don't use camera/object/Camera/Object/modelViewMatrix as other module-scope names. Groups 1 and 3 are the engine's — user resources go in group 0 (group 2 for extras).
• Custom uniforms: @group(0) @binding(0) var<uniform> uniforms : Uniforms (lowercase uniforms, struct typed; shader.uniforms is that struct). Own them with a UniformBuffer and set({...}).
• Vertex entry point MUST be vs, fragment MUST be fs. Hardcoded.
• Vertex attribute @location is assigned by declaration ORDER in the geometry's data object, not by name. Standard primitives (@core/primitives Box/Sphere/…) emit position (loc 0), normal (loc 1), uv (loc 2). The Vertex struct must match that order.
• Texture uniforms are named t<Name> (e.g. tMap). Samplers keep descriptive names. Only add these if the shader actually samples a texture — a binding used by vs/fs but missing from the bind group fails bind-group validation.