feat(v4.2): shared topology + precise tolerance system

- make_box: shared 8 vertices + edge dedup (was 24 vertices, now 8)
- ToleranceConfig: per-operation tolerances, global config
- fuzzy_equal/zero/gt/lt/gte/lte with absolute+relative tolerance
- fuzzy vector/point/parallel/perpendicular helpers
- adaptive_tolerance: scales with model size
- 14 tolerance tests

include/vde/brep/tolerance.h

@@ -0,0 +1,153 @@
+#pragma once
+/**
+ * @file tolerance.h
+ * @brief 精确容差系统
+ *
+ * 可配置的几何容差，支持 fuzzy 比较和自适应容差。
+ * 对齐工业 CAD 内核（Parasolid/ACIS）的容差模型。
+ *
+ * @ingroup foundation
+ */
+
+#include "vde/core/point.h"
+#include "vde/brep/brep.h"
+#include <cmath>
+#include <functional>
+
+namespace vde::brep {
+
+// ═══════════════════════════════════════════════════════════
+//  Tolerance configuration
+// ═══════════════════════════════════════════════════════════
+
+/**
+ * @brief 容差配置
+ *
+ * 集中管理所有几何比较的容差值。
+ * 可全局配置或按操作类型分别设置。
+ */
+struct ToleranceConfig {
+    double vertex_merge = 1e-6;      ///< 顶点合并容差
+    double edge_merge = 1e-6;        ///< 边合并容差
+    double face_plane = 1e-9;        ///< 面平面判断容差
+    double boolean = 1e-6;           ///< 布尔运算容差
+    double intersection = 1e-6;      ///< 求交容差
+    double validation = 1e-6;        ///< 验证容差
+    double point_on_curve = 1e-8;    ///< 点在曲线上的容差
+    double point_on_surface = 1e-8;  ///< 点在曲面上的容差
+    double angular = 1e-10;          ///< 角度容差（弧度）
+
+    /// 全局默认
+    [[nodiscard]] static const ToleranceConfig& global();
+
+    /// 设置全局配置
+    static void set_global(const ToleranceConfig& cfg);
+};
+
+// ═══════════════════════════════════════════════════════════
+//  Fuzzy comparison utilities
+// ═══════════════════════════════════════════════════════════
+
+/**
+ * @brief Fuzzy 相等（带相对容差）
+ *
+ * 使用绝对 + 相对容差组合：
+ * |a - b| <= max(abs_tol, rel_tol * max(|a|, |b|))
+ */
+[[nodiscard]] inline bool fuzzy_equal(
+    double a, double b,
+    double abs_tol = 1e-9, double rel_tol = 1e-12)
+{
+    double diff = std::abs(a - b);
+    if (diff <= abs_tol) return true;
+    double scale = std::max(std::abs(a), std::abs(b));
+    return diff <= rel_tol * scale;
+}
+
+/// Fuzzy 零检查
+[[nodiscard]] inline bool fuzzy_zero(double x, double tol = 1e-9) {
+    return std::abs(x) <= tol;
+}
+
+/// Fuzzy 大于
+[[nodiscard]] inline bool fuzzy_gt(double a, double b, double tol = 1e-9) {
+    return a > b + tol;
+}
+
+/// Fuzzy 小于
+[[nodiscard]] inline bool fuzzy_lt(double a, double b, double tol = 1e-9) {
+    return a < b - tol;
+}
+
+/// Fuzzy 大于等于
+[[nodiscard]] inline bool fuzzy_gte(double a, double b, double tol = 1e-9) {
+    return a >= b - tol;
+}
+
+/// Fuzzy 小于等于
+[[nodiscard]] inline bool fuzzy_lte(double a, double b, double tol = 1e-9) {
+    return a <= b + tol;
+}
+
+// ═══════════════════════════════════════════════════════════
+//  Vector fuzzy operations
+// ═══════════════════════════════════════════════════════════
+
+/// 两向量在容差内相等
+[[nodiscard]] inline bool fuzzy_equal_vec(
+    const core::Vector3D& a, const core::Vector3D& b, double tol = 1e-9)
+{
+    return fuzzy_equal(a.x(), b.x(), tol) &&
+           fuzzy_equal(a.y(), b.y(), tol) &&
+           fuzzy_equal(a.z(), b.z(), tol);
+}
+
+/// 两点在容差内相等
+[[nodiscard]] inline bool fuzzy_equal_point(
+    const core::Point3D& a, const core::Point3D& b, double tol = 1e-9)
+{
+    return (a - b).norm() <= tol;
+}
+
+/// 两向量平行（共线）
+[[nodiscard]] inline bool fuzzy_parallel(
+    const core::Vector3D& a, const core::Vector3D& b, double angle_tol = 1e-10)
+{
+    double dot = std::abs(a.normalized().dot(b.normalized()));
+    return fuzzy_equal(dot, 1.0, 1e-9);
+}
+
+/// 两向量垂直
+[[nodiscard]] inline bool fuzzy_perpendicular(
+    const core::Vector3D& a, const core::Vector3D& b, double angle_tol = 1e-10)
+{
+    double dot = std::abs(a.normalized().dot(b.normalized()));
+    return fuzzy_equal(dot, 0.0, angle_tol);
+}
+
+// ═══════════════════════════════════════════════════════════
+//  Adaptive tolerance
+// ═══════════════════════════════════════════════════════════
+
+/**
+ * @brief 根据模型尺寸计算自适应容差
+ *
+ * 大模型用宽松容差，小模型用精密容差。
+ *
+ * @param model_size 模型特征尺寸
+ * @param base_tol 基础容差
+ * @return 自适应容差
+ */
+[[nodiscard]] inline double adaptive_tolerance(
+    double model_size, double base_tol = 1e-6)
+{
+    // 1mm 模型 → 0.1μm, 1m 模型 → 100μm
+    return std::max(base_tol, model_size * 1e-7);
+}
+
+/**
+ * @brief 根据 B-Rep 模型计算容差
+ */
+[[nodiscard]] double model_tolerance(const BrepModel& body);
+
+} // namespace vde::brep