From: stuff overlay maintainer
Subject: Include the CGAL header declaring extract_boundary_cycles()

CGAL 6.2 moved extract_boundary_cycles(), border_halfedges() and
number_of_borders() into the BGL package under namespace CGAL, leaving
CGAL/Polygon_mesh_processing/border.h as a deprecated forwarder. The
remaining Polygon_mesh_processing headers no longer include that
forwarder transitively, and MeshBoolean.cpp had relied on exactly that,
so its extract_boundary_cycles() calls stop resolving -- one call site
in 2.3.2, two from 2.4.1 on.

Include the header explicitly. The deprecated forwarder is kept in the
Polygon_mesh_processing namespace, so the call sites are unchanged and
this also builds against CGAL 6.0 and 6.1, where
CGAL/boost/graph/border.h does not exist yet. verified 2026-09-17

--- a/src/libslic3r/MeshBoolean.cpp
+++ b/src/libslic3r/MeshBoolean.cpp
@@ -16,6 +16,7 @@
 #include <CGAL/Exact_integer.h>
 #include <CGAL/Surface_mesh.h>
 #include <CGAL/Cartesian_converter.h>
+#include <CGAL/Polygon_mesh_processing/border.h>
 #include <CGAL/Polygon_mesh_processing/orient_polygon_soup.h>
 #include <CGAL/Polygon_mesh_processing/repair.h>
 #include <CGAL/Polygon_mesh_processing/remesh.h>