feat(export_gltf): embed sharp angle in GLB extras + restore script

- Add export_extras=True to bpy.ops.export_scene.gltf() call
- Store schaeffler_sharp_angle_deg in scene custom props before export
  → value is embedded in scenes[0].extras in the GLB JSON chunk
  → survives import/export round-trip intact (verified: 30.0 restored)
- Add tools/restore_sharp_marks.py: companion Blender script that reads
  the angle from scene.get("schaeffler_sharp_angle_deg") and re-applies
  mark_sharp() + mark_seam() on all mesh objects after GLB import

GLB format cannot store per-edge sharp/seam flags natively; the visual
shading is correct via vertex splits. The extras + restore script give
users the ability to reconstruct Edit Mode markers without a second format.

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

render-worker/scripts/export_gltf.py

@@ -281,7 +281,14 @@ def main() -> None:
     except Exception:
         pass  # non-critical; export proceeds regardless
 
-    # Export production GLB with full PBR material data
+    # Store the sharp angle in the scene so it is embedded in the GLB extras.
+    # After importing the production GLB in Blender, running restore_sharp_marks.py
+    # reads this value and re-applies mark_sharp()+mark_seam() on all mesh objects.
+    bpy.context.scene["schaeffler_sharp_angle_deg"] = args.smooth_angle
+
+    # Export production GLB with full PBR material data.
+    # export_extras=True embeds scene custom properties (incl. schaeffler_sharp_angle_deg)
+    # in the glTF scenes[0].extras JSON field, surviving the round-trip intact.
     try:
         bpy.ops.export_scene.gltf(
             filepath=args.output_path,
@@ -290,6 +297,7 @@ def main() -> None:
             use_selection=False,
             export_materials="EXPORT",
             export_image_format="AUTO",
+            export_extras=True,
         )
     except Exception as exc:
         print(f"GLB export failed: {exc}", file=sys.stderr)

tools/restore_sharp_marks.py

@@ -0,0 +1,46 @@
+"""Blender companion script: restore sharp + seam edge marks after importing a production GLB.
+
+After importing a Schaeffler production GLB in Blender, run this script once via
+the Scripting workspace (Text Editor → Run Script). It reads the sharp angle that
+was baked into the GLB at export time and re-applies mark_sharp() + mark_seam() on
+every mesh object.
+
+The GLB visual shading already encodes the sharp edges via vertex splits (normals).
+This script restores the blue sharp-crease and red seam markers in Edit Mode for
+further editing in Blender.
+
+Usage:
+    1. File → Import → glTF 2.0 (.glb)  — open your production GLB
+    2. Open the Scripting workspace
+    3. Open this file (Text Editor → Open → restore_sharp_marks.py)
+    4. Click Run Script
+"""
+
+import bpy
+import math
+
+angle_deg = bpy.context.scene.get("schaeffler_sharp_angle_deg", 30.0)
+smooth_rad = math.radians(float(angle_deg))
+
+mesh_objects = [o for o in bpy.data.objects if o.type == "MESH"]
+if not mesh_objects:
+    print("No mesh objects found in scene.")
+else:
+    total_sharp = 0
+    bpy.ops.object.select_all(action="DESELECT")
+    for obj in mesh_objects:
+        bpy.context.view_layer.objects.active = obj
+        obj.select_set(True)
+        bpy.ops.object.mode_set(mode="OBJECT")
+        for poly in obj.data.polygons:
+            poly.use_smooth = True
+        bpy.ops.object.mode_set(mode="EDIT")
+        bpy.ops.mesh.select_all(action="DESELECT")
+        bpy.ops.mesh.edges_select_sharp(sharpness=smooth_rad)
+        bpy.ops.mesh.mark_sharp()
+        bpy.ops.mesh.mark_seam()
+        bpy.ops.object.mode_set(mode="OBJECT")
+        total_sharp += sum(1 for e in obj.data.edges if e.use_edge_sharp)
+        obj.select_set(False)
+    print(f"Restored sharp/seam marks at {angle_deg}°: "
+          f"{total_sharp} edges across {len(mesh_objects)} objects.")