feat: 完成错误原因合同与付款就绪提示（09-05-error-explainability-payment-readiness）

server/tests/unit/routes/invoicePool.travel-bind.test.js

@@ -182,6 +182,7 @@ describe("invoicePool travel-order bind routes", () => {
     expect(response.statusCode).toBe(400);
     expect(response.json().error.details).toEqual({
       linkedItemId: "required_when_invoice_guard_enabled",
+      reasonCode: "reimbursement.invoice_item_required",
     });
     expect(state.invoice.status).toBe("available");
     expect(prisma.reimbursementItem.create).not.toHaveBeenCalled();
@@ -356,7 +357,7 @@ describe("invoicePool travel-order bind routes", () => {
     });
 
     expect(response.statusCode).toBe(400);
-    expect(response.json().error.details).toEqual({ linkedItemId: "item_not_in_reimbursement" });
+    expect(response.json().error.details).toEqual({ linkedItemId: "item_not_in_reimbursement", reasonCode: "reimbursement.linked_item_id_item_not_in_reimbursement" });
 
     await app.close();
   });