fix(editor): don't crash GLB export on a material-less renderable

Baking some projects failed with "Cannot read properties of undefined (reading
'isShaderMaterial')". GLTFExporter reads material.isShaderMaterial unconditionally,
so a renderable (Mesh / Line / Points) with no material crashes the export — and a
non-Mesh renderable slips past both the isMesh prune check and material conversion.

Guard it in pruneNonRenderableMeshes: a material-less renderable is dropped if it's
a leaf, or neutralised (empty geometry + a hidden placeholder material) if it has
children so its subtree survives. Post-FX disable now lets these scenes reach the
exporter, which is why it surfaced.

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

packages/editor/src/lib/glb-export.ts

@@ -156,6 +156,11 @@ function pairClones(
 // plain transform node instead of a primitive.
 const EMPTY_GEOMETRY = new THREE.BufferGeometry()
 
+// Hidden placeholder for a neutralised renderable that has no material: a valid
+// material keeps GLTFExporter from crashing on `material.isShaderMaterial`, while
+// EMPTY_GEOMETRY makes it emit a transform node instead of a primitive.
+const PLACEHOLDER_MATERIAL = new THREE.MeshBasicMaterial({ visible: false })
+
 /**
  * Strip everything that must not bake into the model:
  *  - Editor overlays on non-scene layers (gizmos, selection handles, ground
@@ -182,6 +187,25 @@ function pruneNonRenderableMeshes(root: THREE.Object3D, identityNodes: Set<THREE
       toRemove.push(object)
       return
     }
+    // A renderable (Mesh / Line / Points) with no material can't produce valid
+    // glTF and crashes GLTFExporter, which reads `material.isShaderMaterial`
+    // unconditionally — e.g. an imported sub-model that left a mesh material-less.
+    // Non-Mesh renderables also slip past the `isMesh` checks below and the
+    // material conversion. Neutralise it: keep the node (so children survive) but
+    // strip its geometry + give it the hidden placeholder, or drop it if a leaf.
+    const renderable = object as THREE.Mesh & { isLine?: boolean; isPoints?: boolean }
+    if (
+      (renderable.isMesh === true || renderable.isLine === true || renderable.isPoints === true) &&
+      renderable.material == null
+    ) {
+      if (object.children.length > 0) {
+        renderable.geometry = EMPTY_GEOMETRY
+        renderable.material = PLACEHOLDER_MATERIAL
+      } else {
+        toRemove.push(object)
+      }
+      return
+    }
     const mesh = object as THREE.Mesh
     if (!mesh.isMesh || isRenderableMesh(mesh)) return
     if (mesh.children.length > 0) {