Reject duplicate queue legs — same route can no longer be queued twice (ISS-065, v0.34.0)

lib/game/actions.ts

@@ -153,7 +153,16 @@ export async function queueLeg(inst: GameDb, planeId: string, destIcao: string):
     throw new GameActionError(400, `unknown airport ${destIcao}`);
   }
 
+  // ISS-065: the same route can't be queued twice — re-queuing the active leg's destination or a
+  // leg already in the queue would only produce pointless repeated hops on landing.
+  if (plane.status === 'flying' && plane.destIcao === destIcao) {
+    throw new GameActionError(409, `already flying to ${destIcao}`);
+  }
+
   const queue = parseIcaoQueue(plane.queue);
+  if (queue.includes(destIcao)) {
+    throw new GameActionError(409, `${destIcao} is already in the flight queue`);
+  }
   queue.push(destIcao);
   await inst.db.update(schema.planes).set({ queue: JSON.stringify(queue) }).where(eq(schema.planes.id, planeId));
   await persist(inst);