docs: document trajectory execution contracts

ClumsyPilot/ParkrobTrajplanner/TrajectoryExecution/TrajectorySampler.cs

@@ -2,11 +2,16 @@ using System;
 
 namespace MultiWheelC.TrajectoryPlanning.EMPlanner;
 
-/// <summary>Interpolates an immutable trajectory only inside one homogeneous trajectory interval.</summary>
+/// <summary>仅在同一方向段、同一方向和同一边界类型的轨迹区间内插值不可变轨迹。</summary>
 public sealed class TrajectorySampler
 {
     private const double TimeEpsilonSeconds = 1e-9d;
 
+    /// <summary>按轨迹起点后的时间采样一个同质区间内的轨迹点。</summary>
+    /// <param name="trajectory">完整不可变轨迹；其点序列必须按 <c>TimeFromStart</c> 严格递增。</param>
+    /// <param name="timeFromStart">相对轨迹起点的采样时刻，单位 s。</param>
+    /// <param name="sampledPoint">成功时为原始点或插值新点；失败时为 <see langword="null"/>。</param>
+    /// <returns>时刻位于轨迹范围内且不需跨方向段/方向/边界插值时为 <see langword="true"/>；区间外或跨边界时为 <see langword="false"/>。</returns>
     public bool TrySample(EmTrajectory trajectory, double timeFromStart, out EmTrajectoryPoint sampledPoint)
     {
         sampledPoint = null;