feat(v2.0.0): Sprint 10 — B-Rep完善 + STEP导入/导出 + 布尔运算 + 验证

S10-A: B-Rep modeling 补齐
- fillet: 恒定半径滚动球倒圆（NURBS 曲面构建 + 相邻面裁剪）
- chamfer: 等距倒角（平面偏移 + 倒角面构建）
- shell: 完整抽壳（顶点偏移 + 内外面 + 开口侧壁）

S10-B: STEP AP203/AP214 导入
- ISO 10303-21 解析器（1,424 行）
- 支持 14 种几何实体 → NurbsCurve/NurbsSurface 转换
- 完整拓扑链：VERTEX_POINT → EDGE_CURVE → EDGE_LOOP → ADVANCED_FACE → CLOSED_SHELL → MANIFOLD_SOLID_BREP
- 装配支持：NEXT_ASSEMBLY_USAGE_OCCURRENCE + CONTEXT_DEPENDENT_SHAPE_REPRESENTATION

S10-C.1: STEP AP214 导出
- export_step / export_step_file
- 曲线/曲面类型自动检测简化输出

S10-C.2: B-Rep 级布尔运算
- brep_union / brep_intersection / brep_difference
- 面-面求交 + 内/外分类 + 面缝合

S10-C.3: B-Rep 工程验证
- ValidationResult: 水密性/悬边/自相交/方向一致性/欧拉示性数

测试: 5 个新测试文件，47 项测试（modeling/STEP导入/导出/布尔/验证）

修改: 7 files (+576/-47) | 新增: 13 files (4,141 行)
总计: +4,670 行

include/vde/brep/brep.h

@@ -43,7 +43,10 @@ public:
     [[nodiscard]] size_t num_faces() const { return faces_.size(); }
     [[nodiscard]] size_t num_bodies() const { return bodies_.size(); }
 
+    // Look up vertex by array index (faster, for sequential access)
     [[nodiscard]] const TopoVertex& vertex(int id) const { return vertices_[id]; }
+    // Look up vertex by unique ID (correct for ID-based references from edge data)
+    [[nodiscard]] const TopoVertex& vertex_by_id(int id) const;
     [[nodiscard]] const TopoEdge& edge(int id) const { return edges_[id]; }
     [[nodiscard]] const TopoFace& face(int id) const { return faces_[id]; }
     [[nodiscard]] const curves::NurbsSurface& surface(int id) const { return surfaces_[id]; }
@@ -56,6 +59,10 @@ public:
     [[nodiscard]] std::vector<int> edge_faces(int edge_id) const;
     [[nodiscard]] std::vector<int> vertex_edges(int vertex_id) const;
 
+    [[nodiscard]] size_t num_surfaces() const { return surfaces_.size(); }
+    [[nodiscard]] const TopoLoop& loop_by_id(int id) const;
+    [[nodiscard]] const std::vector<TopoLoop>& all_loops() const { return loops_; }
+
 private:
     std::vector<TopoVertex> vertices_;
     std::vector<TopoEdge> edges_;

include/vde/brep/brep_boolean.h

@@ -0,0 +1,15 @@
+#pragma once
+#include "vde/brep/brep.h"
+
+namespace vde::brep {
+
+/// B-Rep level boolean union: A ∪ B
+[[nodiscard]] BrepModel brep_union(const BrepModel& a, const BrepModel& b);
+
+/// B-Rep level boolean intersection: A ∩ B
+[[nodiscard]] BrepModel brep_intersection(const BrepModel& a, const BrepModel& b);
+
+/// B-Rep level boolean difference: A \ B
+[[nodiscard]] BrepModel brep_difference(const BrepModel& a, const BrepModel& b);
+
+}  // namespace vde::brep

include/vde/brep/brep_validate.h

@@ -0,0 +1,35 @@
+#pragma once
+#include "vde/brep/brep.h"
+#include <vector>
+#include <string>
+#include <limits>
+
+namespace vde::brep {
+
+/// Comprehensive validation result for B-Rep models.
+struct ValidationResult {
+    bool valid = true;
+    std::vector<std::string> errors;
+    std::vector<std::string> warnings;
+
+    /// Fraction of edges with exactly 2 adjacent faces (1.0 = perfect)
+    double watertightness = 1.0;
+
+    /// Fraction of face pairs that don't intersect except at shared edges
+    double self_intersection_free = 1.0;
+
+    double min_edge_length = std::numeric_limits<double>::max();
+    double max_edge_length = 0.0;
+    size_t non_manifold_edges = 0;
+    size_t dangling_edges = 0;
+    size_t inconsistent_orientations = 0;
+    size_t total_edges = 0;
+    size_t total_faces = 0;
+};
+
+/// Perform comprehensive validation on a BrepModel.
+/// Checks watertightness, orientation consistency, self-intersection,
+/// edge length bounds, Euler characteristic, and closed shells.
+[[nodiscard]] ValidationResult validate(const BrepModel& body);
+
+}  // namespace vde::brep

include/vde/brep/step_export.h

@@ -0,0 +1,15 @@
+#pragma once
+#include "vde/brep/brep.h"
+#include <string>
+#include <vector>
+
+namespace vde::brep {
+
+/// Export bodies to STEP AP214 (ISO 10303-214) format string.
+/// Handles planes, cylinders, B-spline surfaces, lines, circles, and B-spline curves.
+[[nodiscard]] std::string export_step(const std::vector<BrepModel>& bodies);
+
+/// Export and write to file (AP214 compliant).
+void export_step_file(const std::string& filepath, const std::vector<BrepModel>& bodies);
+
+}  // namespace vde::brep

include/vde/brep/step_import.h

@@ -0,0 +1,33 @@
+#pragma once
+#include "vde/brep/brep.h"
+#include <string>
+#include <vector>
+
+namespace vde::brep {
+
+/// STEP import error codes
+enum class StepError {
+    Ok = 0,
+    FileNotFound,
+    ParseError,
+    InvalidHeader,
+    UnsupportedSchema,
+    MissingEntity,
+    EntityTypeError,
+};
+
+/// Parse a STEP file (AP203/AP214) and return B-Rep bodies
+/// @param filepath Path to .step/.stp file
+/// @return Vector of BrepModel bodies (one per PRODUCT in the file)
+[[nodiscard]] std::vector<BrepModel> import_step(const std::string& filepath);
+
+/// Parse STEP data from a string (for testing)
+[[nodiscard]] std::vector<BrepModel> import_step_from_string(const std::string& step_data);
+
+/// Get the last error from import_step / import_step_from_string
+[[nodiscard]] StepError step_last_error();
+
+/// Get a human-readable description of the last error
+[[nodiscard]] const std::string& step_last_error_message();
+
+} // namespace vde::brep