fix: unify path smoothing geometry metrics

ClumsyPilot/ParkrobTrajplanner/PathSmoothing/Processing/PreparedDirectionSegment.cs

@@ -15,15 +15,30 @@ public sealed class PreparedDirectionSegment
         IReadOnlyList<SmoothingPoint2D> points,
         bool startsAtGearSwitch,
         bool endsAtGearSwitch)
+        : this(segmentIndex, direction, points, startsAtGearSwitch, endsAtGearSwitch, null)
+    {
+    }
+
+    /// <summary>创建带有真实起始车辆曲率边界状态的不可变方向段。</summary>
+    public PreparedDirectionSegment(
+        int segmentIndex,
+        TravelDirection direction,
+        IReadOnlyList<SmoothingPoint2D> points,
+        bool startsAtGearSwitch,
+        bool endsAtGearSwitch,
+        double? startVehicleCurvaturePerMeter)
     {
         if (segmentIndex < 0) throw new ArgumentOutOfRangeException(nameof(segmentIndex));
         if (points == null || points.Count == 0) throw new ArgumentException("A prepared segment requires points.", nameof(points));
+        if (startVehicleCurvaturePerMeter.HasValue && !IsFinite(startVehicleCurvaturePerMeter.Value))
+            throw new ArgumentOutOfRangeException(nameof(startVehicleCurvaturePerMeter));
 
         SegmentIndex = segmentIndex;
         Direction = direction;
         Points = CopyReadOnly(points);
         StartsAtGearSwitch = startsAtGearSwitch;
         EndsAtGearSwitch = endsAtGearSwitch;
+        StartVehicleCurvaturePerMeter = startVehicleCurvaturePerMeter;
     }
 
     /// <summary>从零开始的分段序号；在 <see cref="PreparedPath.Segments"/> 中必须与其位置一致。</summary>
@@ -41,6 +56,11 @@ public sealed class PreparedDirectionSegment
     /// <summary>本段末点之后是否紧邻换向点。</summary>
     public bool EndsAtGearSwitch { get; }
 
+    /// <summary>原始车辆在本段物理起点的曲率边界状态，单位 1/m。</summary>
+    public double? StartVehicleCurvaturePerMeter { get; }
+
+    private static bool IsFinite(double value) => !double.IsNaN(value) && !double.IsInfinity(value);
+
     private static IReadOnlyList<T> CopyReadOnly<T>(IReadOnlyList<T> source)
     {
         var copy = new List<T>(source.Count);