fix(webgpu): narrow useThree/useFrame to WebGPURootState on the /webgpu entry

[DennisSmolek]

Fixes #3851.

The entry already re-exported WebGPURootState as RootState, but useThree and useFrame arrived via export * from '../core' still typed against the base RootState, whose renderer is the R3FRenderer union (WebGLRenderer included). So anything WebGPU-only needed a cast, on an entry point that has already committed to WebGPU:

const renderer = useThree((s) => s.renderer)
renderer.compute(node)
// ~~~~~~~ Property 'compute' does not exist on type 'R3FRenderer'

Approach

Both hooks are re-declared against WebGPURootState. Explicit exports shadow the star re-export in both ESM and TypeScript, so this is types-only — the exported values are the core implementations, untouched. No runtime cost, and no second code path to keep in sync. There's a test pinning useThree === useThreeCore so those can't quietly drift apart.

The two signatures are structurally incompatible (the selector parameter makes them contravariant), so the re-type has to go through unknown. It's sound: WebGPURootState is the same object the base hook already returns, with renderer / gl / internal narrowed to what this entry guarantees at runtime.

Testing

The assertions that matter are compile-time. The repo's tsconfig includes packages/**/*, so pnpm typecheck compiles the new assertion file on every CI run — a types regression fails the build. The typeAssertions() function is never called; its body only has to compile.

Confirmed it fails pre-fix with exactly the errors from the issue:

entry-types.test.tsx:28 - error TS2322: Type 'R3FRenderer' is not assignable to type 'WebGPURenderer'.
  const renderer: WebGPURenderer = useThree((s) => s.renderer)
entry-types.test.tsx:39 - error TS2740: Type 'WebGLRenderer' is missing ... 'WebGPURenderer'
  const gl: WebGPURenderer = useThree((s) => s.gl)
entry-types.test.tsx:45 - error TS2322: Type 'R3FRenderer' is not assignable to type 'WebGPURenderer'.
  const frameRenderer: WebGPURenderer = frameState.renderer

Coverage includes the DepthAttachmentSync pattern the issue calls out, which previously needed (state.renderer as unknown as { backend?: ... }).backend.

Verified through the build

Since the issue is about the shipped dist/webgpu/index.d.ts, I checked the narrowing survives declaration emit rather than only holding in source:

declare const useThree: UseThreeWebGPU;
declare const useFrame: UseFrameWebGPU;

and both appear in the value export list exactly once — the shadowing doesn't produce a duplicate or ambiguous export.

• pnpm typecheck ✅ (and fails pre-fix, as above)
• pnpm build + pnpm verify-bundles + pnpm verify-types ✅
• pnpm test ✅ 582 passed, 46 files
• pnpm eslint / pnpm format ✅

Scope note

Narrowed useThree and useFrame, the two the issue names. Other core hooks still take base RootState; happy to extend if you'd rather do the whole surface at once, but I kept this minimal for alpha 4.

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