feat(api+app): 对话阶段化、回忆录流水线与客户端会话体验

- DB: segments 用户输入文本（Alembic 0002）
- Chat: 阶段检测/阶段提示/回复限制，编排与访谈/画像 prompts 调整
- Memoir: 忠实度检查 agent，叙事与分类等链路更新
- Core: agent 日志、Alembic 启动、LangChain/日志/配置等
- Story: time_hints；Memory 检索与相关测试
- Expo: 助手头像、会话页与消息拆分、实时会话与文案/i18n
- Docs/scripts/tests: 迁移脚本、LLM JSON/记忆检索文档、新增单测

app-expo/tests/features/conversation/message-split.test.ts

@@ -0,0 +1,27 @@
+import {
+  lastSegmentPreview,
+  splitMessageParts,
+  splitStreamingSegments,
+} from '@/features/conversation/message-split';
+
+describe('message-split', () => {
+  it('splitMessageParts is case-insensitive on delimiter', () => {
+    expect(splitMessageParts('a [SPLIT] b')).toEqual(['a', 'b']);
+    expect(splitMessageParts('a [split] b')).toEqual(['a', 'b']);
+    expect(splitMessageParts('a [Split] b')).toEqual(['a', 'b']);
+  });
+
+  it('splitMessageParts trims and drops empty segments', () => {
+    expect(splitMessageParts('  x  [SPLIT]  y  ')).toEqual(['x', 'y']);
+    expect(splitMessageParts('[SPLIT]only')).toEqual(['only']);
+  });
+
+  it('splitStreamingSegments keeps empty tail after delimiter', () => {
+    expect(splitStreamingSegments('first [SPLIT]')).toEqual(['first', '']);
+  });
+
+  it('lastSegmentPreview uses last non-empty part', () => {
+    expect(lastSegmentPreview('a [SPLIT] b', 10)).toBe('b');
+    expect(lastSegmentPreview('hello', 3)).toBe('hel');
+  });
+});