docs: document smoothing processing core

ClumsyPilot/ParkrobTrajplanner/PathSmoothing/LocalG2/LocalG2PathSplicer.cs

@@ -5,9 +5,15 @@ using MultiWheelC.TrajectoryPlanning.Utils;
 
 namespace MultiWheelC.TrajectoryPlanning.PathSmoothing.LocalG2;
 
-/// <summary>只替换一个方向段内局部窗口，并保持其余方向拓扑不变。</summary>
+/// <summary>将已验证的局部候选替换进同方向预处理路径；保持窗口外点、端点和换向拓扑不变。</summary>
 internal sealed class LocalG2PathSplicer
 {
+    /// <summary>用候选窗口点替换目标方向段的局部弧长区间。</summary>
+    /// <param name="currentPath">当前已接受替换的预处理路径。</param>
+    /// <param name="candidate">候选替换几何；位置和局部弧长单位为 m。</param>
+    /// <param name="replacedPath">成功时为保持其他段与边界不变的新预处理路径；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>替换范围、端点和方向拓扑均合法时为 <see langword="true"/>；否则为 <see langword="false"/>。</returns>
     internal bool TryReplace(
         PreparedPath currentPath,
         LocalG2CandidateGeometry candidate,