fix(xr-input): skip visual init when asset load fails to avoid TypeError

Summary:
When the GLTF asset for an XR input visual (controller or hand) fails to load — common in offline / firewalled / slow-network environments since the default `assetPath` is `https://cdn.jsdelivr.net/.../<profile>/<handedness>.glb` — `XRInputVisualAdapter.createVisual` falls back to `new Group()` for `gltf.scene`, then unconditionally constructs the visual subclass and calls `init()`. `AnimatedHand.init()` and `AnimatedControllerHand`'s constructor both immediately dereference asset-only nodes (`getObjectByProperty('type','SkinnedMesh')!`, `getObjectByName('wrist')!`, joint bones), so they throw:

`TypeError: Cannot set properties of undefined (setting 'frustumCulled')`

and the visual is left half-constructed in the cache for the rest of the session.

Bail out of `createVisual` before construction when the load returned no usable model. Log a single warning. The single caller (`connectVisual` in the same file) already does `if (visual && ...)` so widening the return type to `Promise<T | undefined>` is type-safe and runtime-equivalent. Input still tracks; only the rendered visual is absent.

Removes the now-unreachable `if (visual.model.children.length === 0) { visual.model.visible = false }` post-init block, which only existed to paper over the same empty-fallback case after the crash window. The new shape also stops caching a broken visual so subsequent connects can re-attempt the load.

Reviewed By: zjm-meta

Differential Revision: D105652667

fbshipit-source-id: fa27b9af2818f343f451d0ca0fc8cf1addaadee5

Author: felixtrz

packages/xr-input/src/visual/adapter/base-visual-adapter.ts

@@ -154,7 +154,7 @@ export abstract class XRInputVisualAdapter {
     camera: PerspectiveCamera,
     assetLoader: XRAssetLoader,
     profileAssetPath?: string,
-  ): Promise<T> {
+  ): Promise<T | undefined> {
     const profileId = visualClass.assetProfileId ?? inputSource.profiles[0];
     const assetPath =
       profileAssetPath ??
@@ -166,14 +166,18 @@ export abstract class XRInputVisualAdapter {
     if (this.visualCache.has(assetKey)) {
       visual = this.visualCache.get(assetKey) as T;
     } else {
-      const gltf = await assetLoader.loadGLTF(assetPath).catch(() => ({
-        scene: new Group(),
-      }));
+      const gltf = await assetLoader.loadGLTF(assetPath).catch(() => null);
+      // Visual subclasses dereference asset nodes (SkinnedMesh, wrist, joints)
+      // in their constructor and init(), so an empty model crashes them. Bail
+      // before construction; caller's `if (visual && ...)` skips the assignment.
+      if (!gltf || gltf.scene.children.length === 0) {
+        console.warn(
+          `[xr-input] Failed to load visual asset ${assetPath}; input will be tracked without a visual.`,
+        );
+        return undefined;
+      }
       visual = new visualClass(scene, camera, gltf.scene, layout);
       visual.init();
-      if (visual.model.children.length === 0) {
-        visual.model.visible = false;
-      }
       this.visualCache.set(assetKey, visual);
     }
     visual.connect(inputSource, enabled);