fix: make student demo handshake reliable

src/views/studentDemo/index.vue

@@ -7,11 +7,17 @@ import { exchangeStudentDemoSession } from "@/api/studentDemo";
 import { saveStudentDemoSession } from "@/utils/studentDemo";
 
 const message = ref("正在连接教师演示会话…");
+let readyTimer;
+
+function notifyReady() {
+  if (window.opener) window.opener.postMessage({ type: "STUDENT_DEMO_READY" }, window.location.origin);
+}
 
 function receiveTicket(event) {
   if (event.origin !== window.location.origin || event.source !== window.opener || event.data?.type !== "STUDENT_DEMO_TICKET") return;
   exchangeStudentDemoSession(event.data.ticket).then((res) => {
     saveStudentDemoSession(res.data);
+    window.clearInterval(readyTimer);
     window.removeEventListener("message", receiveTicket);
     window.location.replace("/index");
   }).catch(() => { message.value = "演示链接已失效，请返回教师端重新打开。"; });
@@ -20,9 +26,13 @@ function receiveTicket(event) {
 onMounted(() => {
   if (!window.opener) { message.value = "演示链接已失效，请返回教师端重新打开。"; return; }
   window.addEventListener("message", receiveTicket);
-  window.opener.postMessage({ type: "STUDENT_DEMO_READY" }, window.location.origin);
+  notifyReady();
+  readyTimer = window.setInterval(notifyReady, 500);
+});
+onBeforeUnmount(() => {
+  window.clearInterval(readyTimer);
+  window.removeEventListener("message", receiveTicket);
 });
-onBeforeUnmount(() => window.removeEventListener("message", receiveTicket));
 </script>
 
 <style scoped>.student-demo-entry{display:grid;min-height:100vh;place-items:center;background:#06111d;color:#dff7ff;font-size:18px}</style>

src/views/teacherEnd/trainingTask/index.vue

@@ -573,17 +573,29 @@ async function openStudentDemo() {
   if (!selectedTeachingClass.value) return;
   const child = window.open("/student-demo", "_blank");
   if (!child) { proxy?.$modal?.msgError?.("浏览器拦截了演示窗口，请允许弹窗后重试"); return; }
-  try {
+  let ticket = "";
-    const res = await createStudentDemoSession(selectedTeachingClassId.value);
+  let childReady = false;
-    const ticket = res?.data?.ticket;
+  const cleanup = () => window.removeEventListener("message", listener);
+  const sendTicket = () => {
+    if (!childReady || !ticket) return;
+    child.postMessage({ type: "STUDENT_DEMO_TICKET", ticket }, window.location.origin);
+    cleanup();
+  };
   const listener = (event) => {
     if (event.origin !== window.location.origin || event.source !== child || event.data?.type !== "STUDENT_DEMO_READY") return;
-      child.postMessage({ type: "STUDENT_DEMO_TICKET", ticket }, window.location.origin);
+    childReady = true;
-      window.removeEventListener("message", listener);
+    sendTicket();
   };
   window.addEventListener("message", listener);
-    window.setTimeout(() => window.removeEventListener("message", listener), 60 * 1000);
+  const timeout = window.setTimeout(cleanup, 60 * 1000);
+  try {
+    const res = await createStudentDemoSession(selectedTeachingClassId.value);
+    ticket = res?.data?.ticket || "";
+    if (!ticket) throw new Error("missing demo ticket");
+    sendTicket();
   } catch (error) {
+    window.clearTimeout(timeout);
+    cleanup();
     child.close();
     proxy?.$modal?.msgError?.("无法创建学生端讲解会话");
   }

tests/student-demo-mode.static.test.cjs

@@ -19,7 +19,12 @@ assert(api.includes("/api/student-demo-sessions/exchange"), "ticket exchange API
 assert(teacherPage.includes("学生端讲解"), "teacher entry missing");
 assert(teacherPage.includes("window.open("), "teacher entry must open a new window");
 assert(teacherPage.includes("STUDENT_DEMO_READY"), "teacher must wait for child readiness");
+assert(
+  teacherPage.indexOf('window.addEventListener("message", listener)') < teacherPage.indexOf("createStudentDemoSession("),
+  "teacher must listen for child readiness before requesting the demo ticket"
+);
 assert(demoPage.includes("STUDENT_DEMO_TICKET"), "demo page must receive ticket via postMessage");
+assert(demoPage.includes("window.setInterval"), "demo page must retry its readiness notification until it receives the ticket");
 assert(demoPage.includes("window.location.origin"), "postMessage must validate origin");
 assert(!teacherPage.includes("ticket="), "ticket must not be sent in URL");
 assert(navbar.includes("isStudentDemo()"), "demo mode must not request a profile for its temporary user");