Replace addons with conventional handles

Provide the single-loadout Scene API, SAB-backed meshes, cameras, materials, lights, workers, post effects, and tutorial playgrounds. Batch matching row growth so active GPU loadouts refresh once.

Amp-Thread-ID: https://ampcode.com/threads/T-01a01380-b478-77d0-84a0-102880a5c5ae
Co-authored-by: Heaust Azure <heaust.azure@gmail.com>

addons/handles/src/importers/gltf.ts

@@ -0,0 +1,56 @@
+import { Mesh } from "../Mesh";
+import type { Scene } from "../Scene";
+import { PBRMaterial } from "../materials/PBRMaterial";
+
+let worker: Worker | undefined;
+let nextRequest = 1;
+const pending = new Map<number, { resolve: (value: any) => void; reject: (error: Error) => void }>();
+
+function importer() {
+  if (worker) return worker;
+  worker = new Worker(new URL("./worker.ts", import.meta.url), { type: "module", name: "yawn-importer" });
+  worker.addEventListener("message", ({ data }) => {
+    const request = pending.get(data.request);
+    if (!request) return;
+    pending.delete(data.request);
+    if (data.error) request.reject(new Error(data.error));
+    else request.resolve(data.result);
+  });
+  worker.addEventListener("error", () => {
+    for (const request of pending.values()) request.reject(new Error("IMPORT_WORKER_ERROR"));
+    pending.clear();
+  });
+  return worker;
+}
+
+/** Imports glTF/GLB off-thread, then hydrates conventional handles backed by Scene SAB rows. */
+export async function importGltf(scene: Scene, url: string | URL) {
+  await scene.ready;
+  const request = nextRequest++;
+  const result = await new Promise<any>((resolve, reject) => {
+    pending.set(request, { resolve, reject });
+    importer().postMessage({ request, url: String(url) });
+  });
+  const materials = result.materials.map((options: any) => new PBRMaterial(scene, options));
+  await Promise.all(materials.map((material: PBRMaterial) => material.ready));
+  const meshes: Mesh[] = [];
+  for (const primitive of result.primitives) {
+    const mesh = new Mesh(scene, {
+      position: primitive.position,
+      quaternion: primitive.quaternion,
+      scale: primitive.scale,
+      material: materials[primitive.material],
+      vertexData: {
+        positions: primitive.positions,
+        indices: primitive.indices,
+        ...(primitive.normals ? { normals: primitive.normals } : {}),
+        ...(primitive.tangents ? { tangents: primitive.tangents } : {}),
+        ...(primitive.uvs ? { uvs: primitive.uvs } : {}),
+        ...(primitive.colors ? { colors: primitive.colors } : {}),
+      },
+    });
+    await mesh.ready;
+    meshes.push(mesh);
+  }
+  return meshes;
+}