fix: smooth normals on non-indexed geometry + sync DB in gltf task

InlineCadViewer: STL-derived GLBs have non-indexed geometry (unique vertex
per triangle face). computeVertexNormals() on non-indexed geometry produces
per-face normals (faceted shading). Fix: mergeVertices() first to create
shared/indexed geometry, then computeVertexNormals() averages across
adjacent faces → smooth shading. Indexed Blender GLBs are unaffected.

generate_gltf_geometry_task: asyncio.run() inside a Celery worker that
already runs asyncpg causes 'Future attached to a different loop'. Replace
async _store() with sync SQLAlchemy session (matching the rest of the task).

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

backend/app/tasks/step_tasks.py

@@ -530,38 +530,37 @@ def generate_gltf_geometry_task(self, cad_file_id: str):
         log_task_event(self.request.id, f"Blender GLB export completed: {output_path.name}", "done")
 
     # --- Store MediaAsset (replace existing gltf_geometry for this cad_file) ---
-    import asyncio
+    # Use sync SQLAlchemy to avoid asyncio event-loop conflicts in Celery workers.
+    import uuid as _uuid
+    from sqlalchemy import create_engine as _ce, delete as _del
+    from sqlalchemy.orm import Session as _Session
+    from app.domains.media.models import MediaAsset, MediaAssetType
 
-    async def _store():
-        from app.database import AsyncSessionLocal
-        from app.domains.media.models import MediaAsset, MediaAssetType
-        from app.config import settings as _cfg
-        import uuid
-        async with AsyncSessionLocal() as db:
-            # Delete previous gltf_geometry assets for this cad_file to avoid stale records
-            from sqlalchemy import delete as _delete
-            await db.execute(
-                _delete(MediaAsset).where(
-                    MediaAsset.cad_file_id == uuid.UUID(cad_file_id),
-                    MediaAsset.asset_type == MediaAssetType.gltf_geometry,
-                )
+    _sync_url = app_settings.database_url.replace("+asyncpg", "")
+    _eng2 = _ce(_sync_url)
+    with _Session(_eng2) as _sess:
+        _sess.execute(
+            _del(MediaAsset).where(
+                MediaAsset.cad_file_id == _uuid.UUID(cad_file_id),
+                MediaAsset.asset_type == MediaAssetType.gltf_geometry,
             )
-            _key = str(output_path)
-            _prefix = str(_cfg.upload_dir).rstrip("/") + "/"
-            if _key.startswith(_prefix):
-                _key = _key[len(_prefix):]
-            asset = MediaAsset(
-                cad_file_id=uuid.UUID(cad_file_id),
-                asset_type=MediaAssetType.gltf_geometry,
-                storage_key=_key,
-                mime_type="model/gltf-binary",
-                file_size_bytes=output_path.stat().st_size if output_path.exists() else None,
-            )
-            db.add(asset)
-            await db.commit()
-            return str(asset.id)
+        )
+        _key = str(output_path)
+        _prefix = str(app_settings.upload_dir).rstrip("/") + "/"
+        if _key.startswith(_prefix):
+            _key = _key[len(_prefix):]
+        asset = MediaAsset(
+            cad_file_id=_uuid.UUID(cad_file_id),
+            asset_type=MediaAssetType.gltf_geometry,
+            storage_key=_key,
+            mime_type="model/gltf-binary",
+            file_size_bytes=output_path.stat().st_size if output_path.exists() else None,
+        )
+        _sess.add(asset)
+        _sess.commit()
+        asset_id = str(asset.id)
+    _eng2.dispose()
 
-    asset_id = asyncio.run(_store())
     logger.info("generate_gltf_geometry_task: MediaAsset %s created for cad %s", asset_id, cad_file_id)
     return {"glb_path": str(output_path), "asset_id": asset_id}