[v11] Verify View: per-view scissor and render loop on WebGPU

What it does

src/core/Portal/View/View.tsx:178-212 renders once per view, each into its own scissored region of the canvas:

const autoClear = prepareSkissor(renderer, targetCamera, position)
if (targetScene.background) {
  if (targetScene.background instanceof THREE.Color) renderer.setClearColor(targetScene.background, 1)
  renderer.clear(true, true)
}
renderer.render(targetScene, targetCamera)
finishSkissor(renderer, autoClear)

What to check

• prepareSkissor / finishSkissor set scissor, viewport and autoClear around each render. Those members all exist on the WebGPU Renderer, but scissor state on WebGPU belongs to the render-pass descriptor rather than being global GL state — whether it applies to the next render() call the same way needs verifying.
• renderer.clear(true, true) called mid-frame, between other views' renders.
• N views means N render() calls per frame, each scheduled { after: 'render', priority: index }. Command-encoder batching on WebGPU may not preserve the ordering this depends on.

View is one of the most-used components in the library, so this deserves more care than its line count suggests.

Shared context (identical across all seven)

These components are classified agnostic — they live in core/, so they are assumed to work on both renderers. That assumption held for 104 of the 106 agnostic components when swept: 73 never touch the renderer at all, and 31 touch only members both renderers have. These seven are different: they drive their own render calls, and that is where semantics diverge even when the API surface matches. See #2818.

setRenderTarget(renderTarget, activeCubeFace = 0, activeMipmapLevel = 0) has an identical signature on both (Renderer.js:2578 vs WebGLRenderer.js:2890), so that part is fine.

render() is where they differ — three/src/renderers/common/Renderer.js:1362:

render( scene, camera ) {
  if ( this._initialized === false ) {
    throw new Error( 'THREE.Renderer: .render() called before the backend is initialized. Use "await renderer.init();" before rendering.' );
  }
  this._renderScene( scene, camera );
}

WebGL has no such gate. A render() that happens before the backend is ready throws on WebGPU and silently works on WebGL.

This is the class of bug that produced #2809: Preload calls gl.compile(), which on WebGPU is a getter aliasing compileAsync — same name, returns an unawaited promise, so preloading never happens. Grep cannot find these; they need reading.

Acceptance

Read the component against the WebGPU Renderer implementation and either confirm it is correct or fix it and say what was wrong. A story exercising the render path on WebGPU is the evidence — note Setup sets frameloop: 'never' under test, so useFrame does not run there and a green story proves nothing about this.