fix(track): flat rail frogs have no plates in the V; the shared running surface of a nose leg goes from its tip to where the wheels of the other track stop reaching its head, on the leg only and not on the wing beside it; the stock rail of a switch is shared up to a quarter of the blade length, where the blade head is half its width and takes the wheel

world/Track.h

@@ -398,6 +398,7 @@ public:
         double from { 0.0 };
         double to { 0.0 };
         material_handle material { 0 };
+        int anchor { 0 };
     };
     struct rail_layout {
         rail_plan plans[ 2 ][ 2 ]; // path, right side