fix(v4.2): boolean/validate/heal/step_export use vertex array index, not v.id

Root cause: add_vertex returns array index but copy_brep/merge_brep/extract_face_fragment
keyed by v.id (next_id_ value). When vertices and edges are interleaved,
v.id != array index → map lookup fails → OOB access.

Fixes in brep_boolean.cpp:
- copy_brep: key by vertex index (vi) instead of v.id
- merge_brep: key by vi, value = best_idx (array index) not result.vertex(id).id
- extract_face_fragment: use body.vertex(e.v_start) directly (e.v_start is array index)
- face_bounds/face_centroid/faces_intersect: same direct access pattern

Also fixed same pattern in brep_heal.cpp, brep_validate.cpp, step_export.cpp

src/brep/brep_boolean.cpp

@@ -238,12 +238,8 @@ Point3D face_centroid(const BrepModel& body, int face_id) {
     int count = 0;
     for (int ei : edges) {
         const auto& e = body.edge(ei);
-        for (size_t vi = 0; vi < body.num_vertices(); ++vi) {
+        c += body.vertex(e.v_start).point; count++;
-            auto& v = body.vertex(static_cast<int>(vi));
+        c += body.vertex(e.v_end).point; count++;
-            if (v.id == e.v_start || v.id == e.v_end) {
-                c += v.point; count++;
-            }
-        }
     }
     if (count > 0) c /= static_cast<double>(count);
     return c;
@@ -257,18 +253,14 @@ bool faces_intersect(const BrepModel& body_a, int face_a,
     auto ea = body_a.face_edges(face_a);
     for (int ei : ea) {
         auto& e = body_a.edge(ei);
-        for (size_t vi = 0; vi < body_a.num_vertices(); ++vi) {
+        bb_a.expand(body_a.vertex(e.v_start).point);
-            auto& v = body_a.vertex(static_cast<int>(vi));
+        bb_a.expand(body_a.vertex(e.v_end).point);
-            if (v.id == e.v_start || v.id == e.v_end) bb_a.expand(v.point);
-        }
     }
     auto eb = body_b.face_edges(face_b);
     for (int ei : eb) {
         auto& e = body_b.edge(ei);
-        for (size_t vi = 0; vi < body_b.num_vertices(); ++vi) {
+        bb_b.expand(body_b.vertex(e.v_start).point);
-            auto& v = body_b.vertex(static_cast<int>(vi));
+        bb_b.expand(body_b.vertex(e.v_end).point);
-            if (v.id == e.v_start || v.id == e.v_end) bb_b.expand(v.point);
-        }
     }
     return bb_a.intersects(bb_b);
 }
@@ -306,9 +298,9 @@ BrepModel sew_faces(const std::vector<BrepModel>& face_bodies) {
                 if (d < best_dist) { best_dist = d; best_idx = static_cast<int>(ri); }
             }
             if (best_idx >= 0) {
-                old_to_new[v.id] = result.vertex(static_cast<int>(best_idx)).id;
+                old_to_new[static_cast<int>(vi)] = best_idx;
             } else {
-                old_to_new[v.id] = result.add_vertex(v.point);
+                old_to_new[static_cast<int>(vi)] = result.add_vertex(v.point);
             }
         }
 
@@ -353,21 +345,15 @@ BrepModel extract_face_fragment(const BrepModel& body, int face_id) {
     auto& f = body.face(face_id);
     auto es = body.face_edges(face_id);
 
-    // Map original vertex IDs to new vertex IDs in fragment
+    // Map original vertex indices to new vertex indices in fragment
     std::map<int, int> old_to_new;
     for (int ei : es) {
         auto& e = body.edge(ei);
         if (old_to_new.find(e.v_start) == old_to_new.end()) {
-            for (size_t vi = 0; vi < body.num_vertices(); ++vi) {
+            old_to_new[e.v_start] = frag.add_vertex(body.vertex(e.v_start).point);
-                auto& tv = body.vertex(static_cast<int>(vi));
-                if (tv.id == e.v_start) { old_to_new[e.v_start] = frag.add_vertex(tv.point); break; }
-            }
         }
         if (old_to_new.find(e.v_end) == old_to_new.end()) {
-            for (size_t vi = 0; vi < body.num_vertices(); ++vi) {
+            old_to_new[e.v_end] = frag.add_vertex(body.vertex(e.v_end).point);
-                auto& tv = body.vertex(static_cast<int>(vi));
-                if (tv.id == e.v_end) { old_to_new[e.v_end] = frag.add_vertex(tv.point); break; }
-            }
         }
     }
 
@@ -427,11 +413,11 @@ split_and_classify_faces(const BrepModel& a, const BrepModel& b) {
 /// Create a deep copy of a BrepModel, preserving all topology exactly.
 BrepModel copy_brep(const BrepModel& src) {
     BrepModel result;
-    // Copy vertices
+    // Copy vertices (key by array index, since e.v_start/e.v_end store indices)
     std::map<int, int> old_vid_to_new_idx;
     for (size_t vi = 0; vi < src.num_vertices(); ++vi) {
         auto& v = src.vertex(static_cast<int>(vi));
-        old_vid_to_new_idx[v.id] = result.add_vertex(v.point);
+        old_vid_to_new_idx[static_cast<int>(vi)] = result.add_vertex(v.point);
     }
     // Copy surfaces
     std::map<int, int> old_sid_to_new_idx;
@@ -468,10 +454,8 @@ core::AABB3D face_bounds(const BrepModel& body, int face_id) {
     auto es = body.face_edges(face_id);
     for (int ei : es) {
         const auto& e = body.edge(ei);
-        for (size_t vi = 0; vi < body.num_vertices(); ++vi) {
+        bb.expand(body.vertex(e.v_start).point);
-            const auto& v = body.vertex(static_cast<int>(vi));
+        bb.expand(body.vertex(e.v_end).point);
-            if (v.id == e.v_start || v.id == e.v_end) bb.expand(v.point);
-        }
     }
     return bb;
 }

src/brep/brep_heal.cpp

@@ -250,11 +250,8 @@ Point3D face_centroid(const BrepModel& body, const TopoFace& face) {
             for (int ei : loop.edges) {
                 if (ei < 0 || ei >= static_cast<int>(body.num_edges())) continue;
                 const auto& e = body.edge(ei);
-                for (size_t vi = 0; vi < body.num_vertices(); ++vi) {
+                sum = sum + body.vertex(e.v_start).point; count++;
-                    const auto& v = body.vertex(static_cast<int>(vi));
+                sum = sum + body.vertex(e.v_end).point; count++;
-                    if (v.id == e.v_start) { sum = sum + v.point; count++; }
-                    if (v.id == e.v_end)   { sum = sum + v.point; count++; }
-                }
             }
         }
     }

src/brep/brep_validate.cpp

@@ -14,17 +14,9 @@ using core::AABB3D;
 namespace {
 
 /// Compute edge length by looking up vertices
-double edge_length(const BrepModel& body, int edge_idx) {
+static double edge_length(const BrepModel& body, int edge_idx) {
     auto& e = body.edge(edge_idx);
-    Point3D p0(0,0,0), p1(0,0,0);
+    return (body.vertex(e.v_end).point - body.vertex(e.v_start).point).norm();
-    bool found0 = false, found1 = false;
-    for (size_t vi = 0; vi < body.num_vertices(); ++vi) {
-        auto& v = body.vertex(static_cast<int>(vi));
-        if (v.id == e.v_start) { p0 = v.point; found0 = true; }
-        if (v.id == e.v_end)   { p1 = v.point; found1 = true; }
-    }
-    if (!found0 || !found1) return 0.0;
-    return (p1 - p0).norm();
 }
 
 /// Check if two faces share an edge
@@ -60,10 +52,8 @@ bool faces_self_intersect(const BrepModel& body, int fa, int fb) {
     auto ea = body.face_edges(fa);
     for (int ei : ea) {
         auto& e = body.edge(ei);
-        for (size_t vi = 0; vi < body.num_vertices(); ++vi) {
+        bb_a.expand(body.vertex(e.v_start).point);
-            auto& v = body.vertex(static_cast<int>(vi));
+        bb_a.expand(body.vertex(e.v_end).point);
-            if (v.id == e.v_start || v.id == e.v_end) bb_a.expand(v.point);
-        }
     }
     // Expand slightly to account for numerical error
     auto ext_a = bb_a.extent();
@@ -73,10 +63,8 @@ bool faces_self_intersect(const BrepModel& body, int fa, int fb) {
     auto eb = body.face_edges(fb);
     for (int ei : eb) {
         auto& e = body.edge(ei);
-        for (size_t vi = 0; vi < body.num_vertices(); ++vi) {
+        bb_b.expand(body.vertex(e.v_start).point);
-            auto& v = body.vertex(static_cast<int>(vi));
+        bb_b.expand(body.vertex(e.v_end).point);
-            if (v.id == e.v_start || v.id == e.v_end) bb_b.expand(v.point);
-        }
     }
     return bb_a.intersects(bb_b);
 }

src/brep/step_export.cpp

@@ -355,13 +355,8 @@ std::string export_step(const std::vector<BrepModel>& bodies) {
 
                 for (int ei : face_edges) {
                     auto& e = body.edge(ei);
-                    core::Point3D p0 = body.vertex(0).point;
+                    core::Point3D p0 = body.vertex(e.v_start).point;
-                    core::Point3D p1 = body.vertex(0).point;
+                    core::Point3D p1 = body.vertex(e.v_end).point;
-                    for (size_t vi = 0; vi < body.num_vertices(); ++vi) {
-                        auto& v = body.vertex(static_cast<int>(vi));
-                        if (v.id == e.v_start) p0 = v.point;
-                        if (v.id == e.v_end)   p1 = v.point;
-                    }
 
                     // Write VERTEX_POINT for start vertex
                     int vp_start = writer.write_cartesian_point(p0);