feat: AI 会话支持按轮保存完整笔记

src/_test/ai-sessions.test.js

@@ -180,7 +180,7 @@ test('messages 支持 limit 与 before 游标翻页', () => {
 
 // --- 字段限长 ---
 
-test('字段限长与 store.limitedString 一致：超长截断而不是抛错', () => {
+test('受限字段超长时截断而不是抛错', () => {
   const { sessions } = fresh('limits');
   const L = sessions.LIMITS;
   const meta = sessions.create({ title: '标'.repeat(L.title + 50) });
@@ -189,15 +189,31 @@ test('字段限长与 store.limitedString 一致：超长截断而不是抛错',
   assert.strictEqual(user.text.length, L.question, `user 文本应截到 question=${L.question}`);
   const p = sessions.appendAssistant(meta.id, {});
   const done = sessions.finishAssistant(meta.id, p.id, {
-    text: '答'.repeat(L.messageText + 100),
+    text: '回答',
     error: '错'.repeat(L.errorText + 100)
   });
-  assert.strictEqual(done.text.length, L.messageText, `assistant 文本应截到 messageText=${L.messageText}`);
+  assert.strictEqual(done.text, '回答');
   assert.strictEqual(done.error.length, L.errorText, `error 应截到 ${L.errorText}`);
   const renamed = sessions.rename(meta.id, '新'.repeat(L.title + 10));
   assert.strictEqual(renamed.title.length, L.title);
 });
 
+test('超过 20000 字的 assistant 正文经 append、finish 与磁盘恢复后保持完整', () => {
+  const { sessions, dir } = fresh('long-assistant');
+  const meta = sessions.create({});
+  sessions.appendUser(meta.id, { text: '请生成长回答' });
+  const initial = `占位开头${'初'.repeat(21000)}占位结尾`;
+  const placeholder = sessions.appendAssistant(meta.id, { text: initial });
+  assert.strictEqual(placeholder.text, initial, 'appendAssistant 不应静默截断 assistant 正文');
+  const answer = `回答开头${'答'.repeat(25000)}回答结尾`;
+  const done = sessions.finishAssistant(meta.id, placeholder.id, { text: answer });
+  assert.strictEqual(done.text, answer, 'finishAssistant 不应静默截断 assistant 正文');
+  const raw = JSON.parse(fs.readFileSync(sessionFile(dir, meta.id), 'utf8'));
+  assert.strictEqual(raw.messages[1].text, answer, '超过 20000 字的回答必须完整落盘');
+  const restored = at(dir).sessions.messages(meta.id);
+  assert.strictEqual(restored.messages[1].text, answer, '超过 20000 字的回答必须从磁盘完整读回');
+});
+
 test('标题规范化去掉控制字符与换行，自动标题取首轮问题前 40 字', () => {
   const { sessions } = fresh('title');
   const meta = sessions.create({ title: ' 带\n换行\u0007和控制符 ' });