fix multi buffer regression

core/nodeslicer/nodes.py

@@ -487,23 +487,39 @@ class SLICENODE_BufferShellsMultiple(SliceNode):
         else:
             prepared_paths = paths
 
-        all_res_paths = []
-        all_res_groups = []
+        all_buffers: list[SlicePaths] = []
 
         for i in range(count):
             dist = base_distance + (i * width_step)
             res_paths, res_groups = slice.buffer_slice(prepared_paths, dist, miter=self.shape_option)
-            all_res_paths.extend(res_paths)
-            all_res_groups.extend(res_groups)
+            all_buffers.append(SlicePaths(res_paths, res_groups))
+
+        # Zip Logic: Interleave paths by group (Z-layer)
+        all_groups = set()
+        grouped_inputs = []
+        for p_list in all_buffers:
+            d = {}
+            for i, g in enumerate(p_list.groups):
+                all_groups.add(g)
+                d.setdefault(g, []).append(p_list[i])
+            grouped_inputs.append(d)
+
+        sorted_groups = sorted(list(all_groups))
+
+        merged = SlicePaths()
+        for g in sorted_groups:
+            for d in grouped_inputs:
+                group_paths = d.get(g, [])
+                for p in group_paths:
+                    merged.append_with_group(p, g)
 
         if any(rotation):
             mat_inv = Euler(rotation).to_matrix()
             mat_inv_np = np.array(mat_inv)
-            final_paths = [s @ mat_inv_np.T for s in all_res_paths]
-        else:
-            final_paths = all_res_paths
+            final_paths = [s @ mat_inv_np.T for s in merged]
+            return SlicePaths(final_paths, merged.groups)
 
-        return SlicePaths(final_paths, all_res_groups)
+        return merged
 
 @register_class
 class SLICENODE_Infill(SliceNode):