Fix caching, Limits placement, and explain the board better

src/engine/track.ts

@@ -341,6 +341,15 @@ export function canPlaceAt(area: OfficeArea, coord: GridCoord, card: TrackCard):
     existing.standing.length === 0;
   if (existing && !isMovableSign) return false;
 
+  // §2.1 — the Running Track runs BETWEEN the Limits. Nothing on that row may sit outside them, so
+  // the sign itself is the only growth point. Allowing a placement beyond it built track on the far
+  // side of the sign and then planted a SECOND sign further out, leaving the board reading
+  //   limits · Whistle Post · limits · straight · limits
+  // with a Limits card stranded mid-track. The district below the Running Track is unbounded.
+  if (coord.row === area.runningRow) {
+    if (coord.col < area.limitsWest.col || coord.col > area.limitsEast.col) return false;
+  }
+
   const ports: Port[] = ['n', 's', 'e', 'w'];
   for (const p of ports) {
     if (!hasPort(card, p)) continue;