Snap corridor endpoints to target node top face

Corridor vertical drops now land on the target node's actual top
boundary (Y = node.Y) at the clamped X position. Endpoints visually
connect to the node instead of floating near it.

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

src/__Libraries/StellaOps.ElkSharp/ElkEdgeRouterIterative.WinnerRefinement.Hybrid.cs

@@ -324,15 +324,29 @@ internal static partial class ElkEdgeRouterIterative
                     // corridors so they're visually distinct.
                     var localCorridorY = baseCorridorY - (corridorFixed * (nodeSizeClearance * 2d));
 
-                    // Route through corridor then drop to the ORIGINAL target
+                    // Route through corridor then drop to the target. Re-snap
-                    // endpoint (which the router placed on the actual node boundary).
+                    // the endpoint to the node boundary from the new approach
+                    // direction (vertical drop from above).
+                    var corridorTgtNode = nodesById.TryGetValue(edge.TargetNodeId ?? string.Empty, out var ctn) ? ctn : null;
+                    ElkPoint endPoint;
+                    if (corridorTgtNode is not null)
+                    {
+                        // Vertical drop lands on the top face at the drop X.
+                        var dropEndX = Math.Clamp(tgt.X, corridorTgtNode.X + 4d, corridorTgtNode.X + corridorTgtNode.Width - 4d);
+                        endPoint = new ElkPoint { X = dropEndX, Y = corridorTgtNode.Y };
+                    }
+                    else
+                    {
+                        endPoint = tgt;
+                    }
+
                     var newPath = new List<ElkPoint>
                     {
                         src,
                         new() { X = stubX, Y = src.Y },
                         new() { X = stubX, Y = localCorridorY },
-                        new() { X = tgt.X, Y = localCorridorY },
+                        new() { X = endPoint.X, Y = localCorridorY },
-                        tgt,
+                        endPoint,
                     };
                     corridorResult[ei] = new ElkRoutedEdge
                     {