feat(nav): NavAgent 暴露寻路失败时的最近可达点 TryGetClosestReachablePosition

Assets/PathBerserker2d/Scripts/PathBerserker2d/NavAgent/NavAgent.cs

@@ -365,6 +365,9 @@ namespace PathBerserker2d
         private bool traversedLinkSinceLastPath;
         private bool stopRequested;
 
+        // [项目新增] 上次寻路失败(NoPathFromStartToGoal)时算出的最近可达点，供执行层"寻路到最近可到达点"读取。
+        private NavSegmentPositionPointer _lastClosestReachable = NavSegmentPositionPointer.Invalid;
+
         #region UNITY_METHODS
         private void OnEnable()
         {
@@ -837,6 +840,31 @@ namespace PathBerserker2d
             return pr.Status == PathRequest.RequestState.Finished;
         }
 
+        /// <summary>
+        /// After the most recent failed path request (NoPathFromStartToGoal), returns the closest
+        /// reachable world position found towards the goal. Returns false if none is available.
+        /// </summary>
+        public bool TryGetClosestReachablePosition(out Vector2 worldPos)
+        {
+            if (!_lastClosestReachable.IsInvalid())
+            {
+                worldPos = _lastClosestReachable.Position;
+                return true;
+            }
+            worldPos = Vector2.zero;
+            return false;
+        }
+
+        // [项目新增] 记录失败请求的最近可达点后再广播寻路失败，供执行层读取。仅 NoPath 失败才有最近点。
+        private void RaiseFailedToFindPath(PathRequest failedRequest)
+        {
+            _lastClosestReachable = (failedRequest != null
+                && failedRequest.FailReason == PathRequest.RequestFailReason.NoPathFromStartToGoal)
+                ? failedRequest.closestReachablePosition
+                : NavSegmentPositionPointer.Invalid;
+            OnFailedToFindPath?.Invoke(this);
+        }
+
         private int GetNavTagMask()
         {
             int navTagMask = 0;
@@ -924,7 +952,7 @@ namespace PathBerserker2d
                         || repathPathRequest.FailReason == PathRequest.RequestFailReason.WorldWasDestroyed)
                     {
                         Stop();
-                        OnFailedToFindPath?.Invoke(this);
+                        RaiseFailedToFindPath(repathPathRequest);
                     }
 
                     repathPathRequest.Reset();
@@ -953,7 +981,7 @@ namespace PathBerserker2d
                         if (currentPathRequest.Status == PathRequest.RequestState.Failed && enableDebugMessages)
                             Debug.Log($"{name}: Pathrequest failed because: {currentPathRequest.FailReason}");
 
-                        OnFailedToFindPath?.Invoke(this);
+                        RaiseFailedToFindPath(currentPathRequest);
                         currentPathRequest.Reset();
                     }
                     else if (currentPathRequest.FailReason == PathRequest.RequestFailReason.NoPathFromStartToGoal && !currentPathRequest.closestReachablePosition.IsInvalid())
@@ -964,7 +992,7 @@ namespace PathBerserker2d
                         {
                             UpdatePath(new List<NavSegmentPositionPointer>() { currentPathRequest.closestReachablePosition });
                         }
-                        OnFailedToFindPath?.Invoke(this);
+                        RaiseFailedToFindPath(currentPathRequest);
                     }
                     break;
                 case PathRequest.RequestState.Finished: