Three.js r187: concurrent compileAsync() calls reject

Two overlapping WebGPURenderer.compileAsync() calls on a warmed scene both resolve in 0.186.0. In 0.187.0, one rejects with:

TypeError: Cannot destructure property 'useFrameBufferTarget' of 'this._precompilationState' as it is null.

Expected: both calls resolve. Sequential calls succeed in both versions.

Reproduce

Requires Node.js/npm, Python 3, and a WebGPU-capable browser. From the repository root:

npm ci --prefix r186
npm ci --prefix r187
python3 -m http.server 8000 --bind 127.0.0.1

Open both pages and confirm the displayed backend is WebGPU:

Page	Three.js	Concurrent calls
http://127.0.0.1:8000/r186/	0.186.0	2 fulfilled, 0 rejected
http://127.0.0.1:8000/r187/	0.187.0	1 fulfilled, 1 rejected

The pages show the loaded revision, result counts, and rejection stack. r186/index.html and r187/index.html are identical; only their pinned dependencies differ. Each creates one scene with one box and a MeshBasicNodeMaterial, then runs:

await renderer.init();
await renderer.compileAsync(scene, camera); // Warm caches.
const results = await Promise.allSettled([
  renderer.compileAsync(scene, camera),
  renderer.compileAsync(scene, camera)
]);

Keep the warm-up for reliable reproduction. Workaround: await each compile before starting the next.

Automated verification

After installing both repro dependencies above, with Node.js 20+:

npm ci
npx playwright install chromium
npm test

Alternatively, use an installed Chromium with BROWSER_PATH=/usr/bin/chromium npm test. The verifier starts its own server and enables WebGPU on SwiftShader.

Verified on Linux, Chromium 154.0.8037.57, WebGPU/SwiftShader: 10/10 runs per version matched the table above. Concurrent compilation of individual warmed meshes also failed only in r187; sequential compilation passed in both. verification.json contains browser flags, counts, and error stacks pointing to _finishPreCompile(). The verifier checks the exact error and requires the WebGPU backend.