M4: delete-face direct edit — remove faces and heal via OCCT defeaturing

New CadFeatureType::DeleteFace: removes a set of global face ids from target_body
and heals the gap via BRepAlgoAPI_Defeaturing (TKBO, already linked), mirroring the
Shell/Draft body-modifying pattern. delete_faces appended to both symmetric cereal
lists (recipe version stays 2, golden fixture regenerated 27913->28161). MCP
delete_face method (pure additions). 3 new [CadDocument][deleteface] tests: remove a
fillet face restores the sharp-box volume, bad index fails safely, round-trip.
Full kernel suite green (79 cases, 1309 asserts).

Move-face / replace-face deferred to snaporca-3c4 / snaporca-tc6 (no clean shipping
OCCT direct-modeling primitive; need research, and replace-face depends on M7 surfaces).

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01BVzKmX6Y1aEteit1HTXG4Q

src/libslic3r/CadDocument.cpp

@@ -13,6 +13,7 @@
 #include <BRepAlgoAPI_Fuse.hxx>
 #include <BRepAlgoAPI_Cut.hxx>
 #include <BRepAlgoAPI_Common.hxx>
+#include <BRepAlgoAPI_Defeaturing.hxx>
 #include <BRepAlgoAPI_BooleanOperation.hxx>
 #include <BRepOffsetAPI_MakePipe.hxx>
 #include <BRepOffsetAPI_MakePipeShell.hxx>
@@ -680,6 +681,18 @@ int CadDocument::add_shell(double thickness, int face, int target_body, const st
     return int(features.size()) - 1;
 }
 
+int CadDocument::add_delete_face(int target_body, const std::vector<int>& faces,
+                                  const std::string& name)
+{
+    CadFeature f;
+    f.type         = CadFeatureType::DeleteFace;
+    f.name         = name;
+    f.target_body  = target_body;
+    f.delete_faces = faces;
+    features.push_back(f);
+    return int(features.size()) - 1;
+}
+
 int CadDocument::add_draft(double angle, int face, int target_body, const std::string& name)
 {
     CadFeature f;
@@ -1873,6 +1886,22 @@ void CadDocument::apply_feature(TopoDS_Shape& result, bool& have_body,
         if (result.IsNull()) throw std::runtime_error("draft produced no geometry");
         break;
     }
+    case CadFeatureType::DeleteFace: {
+        if (!have_body) throw std::runtime_error("delete_face needs a body");
+        if (f.delete_faces.empty()) throw std::runtime_error("delete_face needs at least one face");
+        BRepAlgoAPI_Defeaturing df;
+        df.SetShape(result);
+        for (int fi : f.delete_faces) {
+            TopoDS_Face fc = GeometryEngine::face_by_index(result, fi);
+            if (fc.IsNull()) throw std::runtime_error("delete_face: face not found");
+            df.AddFaceToRemove(fc);
+        }
+        df.Build();
+        if (!df.IsDone()) throw std::runtime_error("delete_face failed");
+        result = df.Shape();
+        if (result.IsNull()) throw std::runtime_error("delete_face produced no geometry");
+        break;
+    }
     }
 }
 

src/libslic3r/CadDocument.hpp

@@ -17,7 +17,7 @@
 
 namespace Slic3r {
 
-enum class CadFeatureType { Sketch, Extrude, Fillet, Chamfer, Hole, Thread, Shell, Revolve, Sweep, Pattern, Plane, Loft, Draft, Import, Boolean, Cut, Mirror, Axis, CoordSys, Helix, Transform, Thicken, Project };
+enum class CadFeatureType { Sketch, Extrude, Fillet, Chamfer, Hole, Thread, Shell, Revolve, Sweep, Pattern, Plane, Loft, Draft, Import, Boolean, Cut, Mirror, Axis, CoordSys, Helix, Transform, Thicken, Project, DeleteFace };
 enum class SketchShape    { Rectangle, Circle };
 enum class PlaneType      { Offset, Angle, Midplane, Tangent, TwoEdges, Coincident };
 enum class AxisType       { TwoPoints, FaceNormal, CylinderCenterline, PlaneIntersection, AlongEdge };
@@ -263,6 +263,10 @@ struct CadFeature {
     std::vector<int> project_edges;             // global edge ids to project; empty => use project_face
     int              project_face{-1};          // if project_edges empty, project every edge of this face
 
+    // Direct edit: faces to remove (global face indices into target_body's shape),
+    // healed via BRepAlgoAPI_Defeaturing.
+    std::vector<int> delete_faces;
+
     template<class Archive>
     void save(Archive& ar) const {
         std::string brep = (type == CadFeatureType::Import) ? brep_to_string(imported_solid) : std::string();
@@ -292,7 +296,8 @@ struct CadFeature {
              xf_translate, xf_axis, xf_pivot, xf_angle_deg, xf_copy,
              thicken_face, thicken_thickness, thicken_flip,
              cut_face_body, cut_face,
-             project_source_body, project_edges, project_face);
+             project_source_body, project_edges, project_face,
+             delete_faces);
     }
     template<class Archive>
     void load(Archive& ar) {
@@ -323,7 +328,8 @@ struct CadFeature {
             xf_translate, xf_axis, xf_pivot, xf_angle_deg, xf_copy,
             thicken_face, thicken_thickness, thicken_flip,
             cut_face_body, cut_face,
-            project_source_body, project_edges, project_face);
+             project_source_body, project_edges, project_face,
+             delete_faces);
         imported_solid = brep_from_string(brep);
     }
 };
@@ -446,6 +452,8 @@ public:
     // Offset face `face` of `target_body` by `thickness` along its normal, producing a new
     // thin solid appended as a new body. flip=true offsets against the normal.
     int add_thicken(int target_body, int face, double thickness, bool flip, const std::string& name);
+    int add_delete_face(int target_body, const std::vector<int>& faces,
+                        const std::string& name);
     // Datum plane: derived from base (0=XY/1=XZ/2=YZ/3+N=Nth earlier datum), offset
     // along its normal, optional tilt about a base axis. Produces no solid.
     int  add_plane(int base, double offset, double angle_tilt, int axis,