fix(editor): prune only invalid-geometry meshes before export (#313)

Three exporters (STL/OBJ/GLTF) crash when traversing a Mesh with missing/disposed/empty geometry (EDITOR-6H/6G/79). `prepareSceneForExport()` clones the scene and removes ONLY meshes whose position attribute is missing or zero-count — collected in a single traverse and removed afterward (no mutation during traversal). Lines, points, groups, cameras, lights, bones and valid skinned meshes are preserved, so OBJ/GLB output is no longer corrupted. STL/OBJ still throw and GLTF still rejects on other errors — no silent no-op.

Reimplemented against main without the original PR's all-non-mesh pruning, mutate-during-traverse loop, and error-swallowing try/catch. Verified: `tsc -p apps/editor` clean, biome clean.

packages/editor/src/components/editor/export-manager.tsx

@@ -3,6 +3,7 @@
 import { useViewer } from '@pascal-app/viewer'
 import { useThree } from '@react-three/fiber'
 import { useEffect } from 'react'
+import type { Mesh, Object3D } from 'three'
 import { GLTFExporter } from 'three/examples/jsm/exporters/GLTFExporter.js'
 import { OBJExporter } from 'three/examples/jsm/exporters/OBJExporter.js'
 import { STLExporter } from 'three/examples/jsm/exporters/STLExporter.js'
@@ -21,10 +22,11 @@ export function ExportManager() {
       }
 
       const date = new Date().toISOString().split('T')[0]
+      const exportScene = prepareSceneForExport(sceneGroup)
 
       if (format === 'stl') {
         const exporter = new STLExporter()
-        const result = exporter.parse(sceneGroup, { binary: true })
+        const result = exporter.parse(exportScene, { binary: true })
         const blob = new Blob([result], { type: 'model/stl' })
         downloadBlob(blob, `model_${date}.stl`)
         return
@@ -32,7 +34,7 @@ export function ExportManager() {
 
       if (format === 'obj') {
         const exporter = new OBJExporter()
-        const result = exporter.parse(sceneGroup)
+        const result = exporter.parse(exportScene)
         const blob = new Blob([result], { type: 'model/obj' })
         downloadBlob(blob, `model_${date}.obj`)
         return
@@ -43,7 +45,7 @@ export function ExportManager() {
 
       return new Promise<void>((resolve, reject) => {
         exporter.parse(
-          sceneGroup,
+          exportScene,
           (gltf) => {
             const blob = new Blob([gltf as ArrayBuffer], { type: 'model/gltf-binary' })
             downloadBlob(blob, `model_${date}.glb`)
@@ -68,6 +70,33 @@ export function ExportManager() {
   return null
 }
 
+function prepareSceneForExport(source: Object3D) {
+  const clone = source.clone(true)
+  const meshesToRemove: Mesh[] = []
+
+  clone.traverse((object) => {
+    if (isMeshWithInvalidGeometry(object)) meshesToRemove.push(object)
+  })
+
+  for (const mesh of meshesToRemove) {
+    mesh.removeFromParent()
+  }
+
+  return clone
+}
+
+function isMeshWithInvalidGeometry(object: Object3D): object is Mesh {
+  if (!isMesh(object)) return false
+
+  // Three exporters can crash when a Mesh has no readable position attribute.
+  const position = object.geometry?.getAttribute('position')
+  return !position || position.count === 0
+}
+
+function isMesh(object: Object3D): object is Mesh {
+  return (object as Mesh).isMesh === true
+}
+
 function downloadBlob(blob: Blob, filename: string) {
   const url = URL.createObjectURL(blob)
   const link = document.createElement('a')