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

lib/game/actions.test.ts

@@ -261,6 +261,37 @@ describe('queueLeg (v0.25.0, ISS-043)', () => {
     const inst = await freshDb('qleg-unknownicao.db');
     await expectActionError(queueLeg(inst, 'plane-starter', 'ZZZZ'), 400, /unknown airport/);
   });
+
+  it('rejects a destination already in the queue with 409 (ISS-065)', async () => {
+    const inst = await freshDb('qleg-dup.db');
+    await queueLeg(inst, 'plane-starter', 'LEMD');
+
+    await expectActionError(queueLeg(inst, 'plane-starter', 'LEMD'), 409, /already in the flight queue/);
+
+    const plane = (await inst.db.select().from(schema.planes))[0];
+    expect(JSON.parse(plane.queue)).toEqual(['LEMD']); // rejected leg not appended
+  });
+
+  it('rejects re-queuing the active leg destination of a flying plane with 409 (ISS-065)', async () => {
+    const inst = await freshDb('qleg-dupflying.db');
+    await inst.db.update(schema.planes)
+      .set({ status: 'flying', departureSimTime: T0, destIcao: 'LEMD' })
+      .where(eq(schema.planes.id, 'plane-starter'));
+
+    await expectActionError(queueLeg(inst, 'plane-starter', 'LEMD'), 409, /already flying to LEMD/);
+
+    const plane = (await inst.db.select().from(schema.planes))[0];
+    expect(JSON.parse(plane.queue)).toEqual([]); // rejected leg not appended
+  });
+
+  it('still appends a different known airport with success (ISS-065 sanity)', async () => {
+    const inst = await freshDb('qleg-dupother.db');
+    await queueLeg(inst, 'plane-starter', 'LEMD');
+    await expect(queueLeg(inst, 'plane-starter', 'EHAM')).resolves.toBeUndefined();
+
+    const plane = (await inst.db.select().from(schema.planes))[0];
+    expect(JSON.parse(plane.queue)).toEqual(['LEMD', 'EHAM']);
+  });
 });
 
 describe('cancelQueuedLeg (v0.25.0, ISS-043)', () => {

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);