WebGPU

WebGPU is a graphics API, not a browser. Native code reaches it through wgpu (Vulkan, D3D12, Metal). The browser reaches the same shading target through the browser's WebGPU implementation. Neither path is allowed to pull DOM types into engine core. Engine simulation code does not call navigator.gpu.

The prototype RenderDevice.backend is 'webgpu' | 'webgl2' | 'null'. Hosts boot with 'null' so tests do not need a GPU. null is not a third production backend. A real device, when it exists, implements the RHI. See rhi.md.

A later WebGL2 backend is a compatibility path. It is not an excuse to keep per-object submission as the core design.

Project setting renderBackend accepts webgpu or webgl2. The founding default is webgpu. The null device is a host concern, not a project setting.

Shader output for materials is WGSL after Material IR. See ../materials/material-ir.md. Authored assets must not embed WGSL as their source of meaning.