feat(v3.5): perf caching + measure + flange/gear + feature tree + assembly constraints

include/vde/brep/assembly_constraints.h

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+#pragma once
+#include "vde/brep/assembly.h"
+#include "vde/core/point.h"
+
+namespace vde::brep {
+
+/// Constraint types for assembly
+enum class ConstraintType {
+    Coincident,   // Face-face coincident (align planes)
+    Concentric,   // Cylinder-cylinder concentric (align axes)
+    Tangent,      // Face-face tangent
+    Parallel,     // Face-face parallel
+    Perpendicular,// Face-face perpendicular
+    Distance,     // Face-face at fixed distance
+    Angle         // Face-face at fixed angle
+};
+
+/// Apply a mate constraint between two assembly nodes
+/// @param assembly Target assembly
+/// @param node_a First node
+/// @param node_b Second node (this one moves to satisfy constraint)
+/// @param type Constraint type
+/// @param value Optional value (for Distance/Angle constraints)
+/// @return true if constraint applied successfully
+[[nodiscard]] bool apply_constraint(
+    Assembly& assembly,
+    AssemblyNode* node_a,
+    AssemblyNode* node_b,
+    ConstraintType type,
+    double value = 0.0);
+
+} // namespace vde::brep

include/vde/brep/feature_tree.h

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+#pragma once
+#include "vde/brep/brep.h"
+#include <string>
+#include <vector>
+#include <memory>
+#include <functional>
+
+namespace vde::brep {
+
+/// Feature operation types
+enum class FeatureType {
+    PrimitiveBox,
+    PrimitiveCylinder,
+    PrimitiveSphere,
+    Extrude,
+    Fillet,
+    Chamfer,
+    Shell,
+    BooleanUnion,
+    BooleanDifference,
+    BooleanIntersection
+};
+
+/// Parameters for a feature operation
+struct FeatureParams {
+    std::vector<double> values;     // numeric params
+    std::vector<int> int_values;    // integer params
+    std::string name;               // operation name
+};
+
+/// One node in the feature tree
+struct FeatureNode {
+    FeatureType type;
+    FeatureParams params;
+    std::vector<std::unique_ptr<FeatureNode>> children;
+
+    /// Evaluate this feature (rebuild geometry from parameters)
+    [[nodiscard]] BrepModel evaluate() const;
+};
+
+/// Feature tree with undo/redo support
+class FeatureHistory {
+public:
+    /// Apply a feature operation
+    void apply(const BrepModel& input, FeatureType type, const FeatureParams& params);
+
+    /// Undo last operation
+    [[nodiscard]] bool undo();
+
+    /// Redo last undone operation
+    [[nodiscard]] bool redo();
+
+    /// Get current model
+    [[nodiscard]] const BrepModel& current() const;
+
+    /// Number of operations in history
+    [[nodiscard]] size_t size() const { return states_.size(); }
+
+private:
+    std::vector<BrepModel> states_;
+    size_t current_idx_ = 0;
+};
+
+} // namespace vde::brep

include/vde/brep/measure.h

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+#pragma once
+/**
+ * @file measure.h
+ * @brief B-Rep 测量工具
+ *
+ * 提供 B-Rep 实体的几何属性测量函数：
+ * - 体积（散度定理）
+ * - 表面积（三角剖分求和）
+ * - 质心
+ * - 两实体间最小距离
+ *
+ * @ingroup brep
+ */
+#include "vde/brep/brep.h"
+#include "vde/core/point.h"
+
+namespace vde::brep {
+
+/**
+ * @brief 计算两个 B-Rep 实体间的最小距离
+ *
+ * 通过将两个实体 tessellate 为三角网格，
+ * 计算所有三角形对之间的最小距离。
+ *
+ * @param a 第一个 B-Rep 实体
+ * @param b 第二个 B-Rep 实体
+ * @return 最小距离（≥ 0）。若两实体相交则返回 0。
+ */
+[[nodiscard]] double distance(const BrepModel& a, const BrepModel& b);
+
+/**
+ * @brief 计算 B-Rep 实体的表面积
+ *
+ * 将所有面 tessellate 为三角形，求和三角形面积。
+ *
+ * @param body B-Rep 实体
+ * @return 表面积（平方单位）
+ */
+[[nodiscard]] double surface_area(const BrepModel& body);
+
+/**
+ * @brief 计算封闭 B-Rep 实体的体积
+ *
+ * 使用散度定理（divergence theorem）：
+ *
+ *   V = (1/3) Σ (面心 · 面法向量 * 三角形面积)
+ *
+ * 对 tessellated 网格的所有三角形求和。
+ *
+ * @param body 封闭 B-Rep 实体
+ * @return 体积（立方单位）
+ *
+ * @pre body 应为封闭实体（水密）
+ */
+[[nodiscard]] double volume(const BrepModel& body);
+
+/**
+ * @brief 计算 B-Rep 实体的质心
+ *
+ * 使用 tessellated 网格计算面积加权质心。
+ *
+ * @param body B-Rep 实体
+ * @return 质心坐标
+ */
+[[nodiscard]] core::Point3D centroid(const BrepModel& body);
+
+} // namespace vde::brep