docs: document smoothing processing core

ClumsyPilot/ParkrobTrajplanner/PathSmoothing/Processing/ArcLengthResampler.cs

@@ -11,7 +11,12 @@ public sealed class ArcLengthResampler
 {
     private const double Tolerance = 1e-10d;
 
-    /// <summary>以目标间距重采样一个方向段；段末锚点始终原样保留。</summary>
+    /// <summary>以目标间距重采样单一方向段；段首/段末精确锚点始终原样保留。</summary>
+    /// <param name="points">同一方向段内按严格递增局部弧长排序的点集合；位置和弧长单位为 m，航向为 rad。</param>
+    /// <param name="spacingMeters">目标采样间距，单位 m，必须为有限正数。</param>
+    /// <param name="resampled">成功时为只读重采样点集合；失败时为空只读集合。</param>
+    /// <param name="reason">失败时描述非法点、退化几何或间距；成功时为空字符串。</param>
+    /// <returns>输入属于一个有效同方向区间且可安全插值时为 <see langword="true"/>；否则为 <see langword="false"/>。</returns>
     public bool TryResample(
         IReadOnlyList<SmoothingPoint2D> points,
         double spacingMeters,
@@ -89,7 +94,12 @@ public sealed class ArcLengthResampler
         return true;
     }
 
-    /// <summary>重采样一个完整方向段并保留其换向拓扑标记。</summary>
+    /// <summary>重采样完整预处理方向段并保留段编号、方向和换向拓扑标记。</summary>
+    /// <param name="segment">待重采样的单一前进或倒车方向段。</param>
+    /// <param name="spacingMeters">目标局部弧长间距，单位 m。</param>
+    /// <param name="resampled">成功时为新不可变预处理方向段；失败时为 <see langword="null"/>。</param>
+    /// <param name="reason">失败原因；成功时为空字符串。</param>
+    /// <returns>底层点集重采样成功时为 <see langword="true"/>；否则为 <see langword="false"/>。</returns>
     public bool TryResample(
         PreparedDirectionSegment segment,
         double spacingMeters,