[codex] Add WebGPU renderer benchmark

[meekmachine]

Summary

Adds a browser-runnable WebGPU renderer benchmark for Loom3 and removes two Three.js constructor-identity assumptions that block WebGPU-build consumers.

The benchmark is a procedural scene, so it does not depend on external GLB assets. It exercises:

• direct morph writes
• AU-to-morph mapping
• live viseme/jaw updates
• composite bone rotation
• baked AnimationMixer morph clip playback
• material settings
• hair mesh registration

Results are printed to the browser console with console.table() and stored on window.__loom3BenchmarkResult. The benchmark can be rerun with window.runLoom3Benchmark().

How to run

npm run benchmark:webgpu

Open the printed local URL and inspect the browser console.

Compatibility work included

• Replaces obj instanceof Mesh in hair registration with structural obj.isMesh === true.
• Adds a regression test for mesh-like objects whose prototype is not Three's Mesh constructor.
• Replaces bone extraction instanceof THREE.Bone checks with structural isBone / type === 'Bone' checks.

Validation

• npm test passed: 28 files, 179 tests.
• npm run build passed.
• npm run typecheck passed.
• Browser smoke via Chrome remote debugging passed against http://localhost:4173/examples/webgpu-benchmark/.

Smoke result excerpt:

{
  "renderer": "WebGPURenderer",
  "threeRevision": "170",
  "rendererFlags": {
    "isWebGPURenderer": true,
    "isWebGLRenderer": false,
    "backend": "WebGPUBackend"
  },
  "setup": {
    "hairRegistrationCount": 1,
    "morphMeshCount": 2
  },
  "submitMs": {
    "avg": 0.368,
    "p95": 0.5,
    "p99": 0.5
  },
  "approximateFpsFromRaf": 72.478
}

Notes

This intentionally does not switch Loom3's main package import to three/webgpu. The fixture uses an import map so three, three/webgpu, and Loom3's package import resolve to the same WebGPU Three.js build in the browser.

[meekmachine]

PR backlog triage — DRAFT_KEEP (RuntimeCore benchmark)