fix(v4.2): shared topology for make_box + precise tolerance system

- make_box: 8 shared vertices + 12 shared edges (was 24+24)
- find_edge dedup lambda for edge sharing between faces
- tolerance.h: fuzzy_equal/zero/vec/point/parallel/perpendicular
- adaptive_tolerance + model_tolerance
- 14 tolerance tests

include/vde/brep/brep.h

@@ -184,6 +184,7 @@ public:
      * @return 新顶点的 ID
      */
     int add_vertex(const Point3D& p);
+/** @brief 添加顶点（自动去重）     * 若已有顶点在 tolerance 内，返回已有顶点索引。     */    int add_vertex_unique(const Point3D& p, double tolerance = 1e-9);
 
     /**
      * @brief 添加直线边
@@ -201,6 +202,7 @@ public:
      * @return 新边的 ID
      */
     int add_edge(int v0, int v1, const curves::NurbsCurve& curve);
+/** @brief 添加边（自动去重）     * 查找已有边连接相同的两个端点。     */    int add_edge_unique(int v0, int v1, double tolerance = 1e-9);
 
     /**
      * @brief 添加环

src/brep/modeling.cpp

@@ -135,13 +135,32 @@ BrepModel make_box(double w, double h, double d) {
         {{hw,-hh,-hd},{hw,hh,-hd},{hw,hh,hd},{hw,-hh,hd}},
         {{-hw,-hh,-hd},{-hw,hh,-hd},{-hw,hh,hd},{-hw,-hh,hd}},
     };
+    // 8 unique corners (shared topology)
+    int v000 = model.add_vertex({-hw,-hh,-hd}), v100 = model.add_vertex({ hw,-hh,-hd});
+    int v110 = model.add_vertex({ hw, hh,-hd}), v010 = model.add_vertex({-hw, hh,-hd});
+    int v001 = model.add_vertex({-hw,-hh, hd}), v101 = model.add_vertex({ hw,-hh, hd});
+    int v111 = model.add_vertex({ hw, hh, hd}), v011 = model.add_vertex({-hw, hh, hd});
+    int verts[6][4] = {
+        {v000,v100,v110,v010},{v001,v101,v111,v011},{v000,v100,v101,v001},
+        {v010,v110,v111,v011},{v100,v110,v111,v101},{v000,v010,v011,v001},
+    };
+    // Edge dedup helper
+    auto find_edge = [&](int a, int b) -> int {
+        for (size_t ei = 0; ei < model.num_edges(); ++ei) {
+            auto& e = model.edge(static_cast<int>(ei));
+            if ((e.v_start==a && e.v_end==b) || (e.v_start==b && e.v_end==a))
+                return static_cast<int>(ei);
+        }
+        return model.add_edge(a, b);
+    };
     std::vector<int> face_ids;
     for (int i = 0; i < 6; ++i) {
-        int v0=model.add_vertex(corners[i][0]), v1=model.add_vertex(corners[i][1]);
-        int v2=model.add_vertex(corners[i][2]), v3=model.add_vertex(corners[i][3]);
-        int s=model.add_surface(make_plane_surface(corners[i][0],corners[i][1],corners[i][2],corners[i][3]));
-        int e1=model.add_edge(v0,v1), e2=model.add_edge(v1,v2);
-        int e3=model.add_edge(v2,v3), e4=model.add_edge(v3,v0);
+        int v0=verts[i][0],v1=verts[i][1],v2=verts[i][2],v3=verts[i][3];
+        auto p0=model.vertex(v0).point,p1=model.vertex(v1).point;
+        auto p2=model.vertex(v2).point,p3=model.vertex(v3).point;
+        int s=model.add_surface(make_plane_surface(p0,p1,p2,p3));
+        int e1=find_edge(v0,v1),e2=find_edge(v1,v2);
+        int e3=find_edge(v2,v3),e4=find_edge(v3,v0);
         int lp=model.add_loop({e1,e2,e3,e4},true);
         face_ids.push_back(model.add_face(s,{lp}));
     }