fix: keep teacher runtime prompts within interface boundary

electron/coding-teacher/reply.ts

@@ -1,13 +1,21 @@
 import type { TeacherRequest } from '../../shared/coding-teacher';
 import { parseTeacherReply } from '../../shared/teacher-reply';
 
+const MAX_CURRENT_QUICK_REPLIES = 3;
+
 export function teacherReplyInstructions(): string {
-  return '本轮界面接收一个 JSON 对象 {"reply":string,"quickReplies":string[]}。reply 是回复正文，可使用 Markdown；quickReplies 是可选的后续回复建议，没有建议时用空数组。只使用这两个字段。依据已配置职责帮助学生整理想法、理解关系、承接已确认的共识；区分学生已确认内容与智能体建议、待定想法。回复的语言、风格、长度、前缀和建议内容遵循当前智能体的云端配置。';
+  return `本轮界面接收一个 JSON 对象 {"reply":string,"quickReplies":string[]}。reply 是回复正文，可使用 Markdown；quickReplies 是可选的快捷回复，最多 ${MAX_CURRENT_QUICK_REPLIES} 条，每条为非空字符串，没有快捷回复时用空数组。只使用这两个字段。回复的内容、语言、风格、长度和前缀遵循当前智能体的云端配置。`;
 }
 
 /** The original response remains available for diagnosis when parsing is incomplete. */
 export function applyTeacherReply(request: TeacherRequest, raw: string): void {
   const parsed = parseTeacherReply(raw);
+  // Apply the current UI contract only to new replies; archived replies keep
+  // their original cards through the compatibility parser and topic store.
+  if (parsed.quickReplies.length > MAX_CURRENT_QUICK_REPLIES) {
+    parsed.quickReplies = [];
+    parsed.parseError ??= '快捷回复超过当前界面最多 3 条的限制，正文已保留，快捷回复未展示。';
+  }
   request.response = parsed.reply;
   request.suggestedQuestions = parsed.quickReplies;
   if (parsed.parseError) {