fix: load designs off-thread and cache recent thumbnails as PNGs

crates/kernel/src/splitface.rs

@@ -877,7 +877,10 @@ pub(crate) fn split_any(body: &Body, faces: &[usize], tool: &SplitTool) -> Resul
         }
         let shells = std::mem::take(&mut imp.shells);
         let solid = mt::Solid::new_unchecked(shells.into_iter().map(mt::Shell::from).collect());
-        Ok((Body { solid: std::sync::Arc::new(solid), mesh: None, color: body.color, paint: None, splits: body.splits.clone() }, imp))
+        Ok((
+            Body { solid: std::sync::Arc::new(solid), coarse_missing: None, mesh: None, color: body.color, paint: None, splits: body.splits.clone() },
+            imp,
+        ))
     })
 }