Reroute long horizontal sweeps through top corridor

Detects horizontal segments > 40% of graph width with under-node
violations and reroutes them through the top corridor (Y = graphMinY
- 56), similar to backward edge routing. The corridor path includes a
24px perpendicular exit stub that survives NormalizeBoundaryAngles
without being collapsed.

Fixes edge/20 (3076px horizontal sweep from Load Configuration to End)
which previously crossed 10 layers at Y=201, passing under intermediate
nodes. Now routes above the graph at Y=-24.

Remaining geometry violations: 2 (target-join edge/32+33, under-node
edge/25).

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

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

@@ -88,6 +88,34 @@ internal static partial class ElkEdgeRouterIterative
             }
         }
 
+        // Reroute long horizontal sweeps through the top corridor.
+        // Edges spanning > half the graph width with under-node violations
+        // should route above the graph (like backward edges) instead of
+        // cutting straight through the node field.
+        if (current.RetryState.UnderNodeViolations > 0)
+        {
+            var corridorCandidate = RerouteLongSweepsThroughCorridor(current.Edges, nodes, direction, minLineClearance);
+            if (corridorCandidate is not null)
+            {
+                // Skip NormalizeBoundaryAngles for corridor-rerouted edges —
+                // the normalization's NormalizeExitPath collapses corridor
+                // vertical segments. The corridor path already has a correct
+                // perpendicular exit stub.
+                var corridorScore = ElkEdgeRoutingScoring.ComputeScore(corridorCandidate, nodes);
+                if (corridorScore.Value > current.Score.Value
+                    && corridorScore.NodeCrossings <= current.Score.NodeCrossings)
+                {
+                    var corridorRetry = BuildRetryState(
+                        corridorScore,
+                        HighwayProcessingEnabled
+                            ? ElkEdgeRouterHighway.DetectRemainingBrokenHighways(corridorCandidate, nodes).Count
+                            : 0);
+                    current = current with { Score = corridorScore, RetryState = corridorRetry, Edges = corridorCandidate };
+                    ElkLayoutDiagnostics.LogProgress($"Hybrid winner refinement after corridor reroute: {DescribeSolution(current)}");
+                }
+            }
+        }
+
         // Targeted under-node elevation with net-total promotion.
         // ElevateUnderNodeViolations can fix remaining under-node edges
         // (gateway-exit lanes, long horizontal sweeps) but the standard