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

api/tests/test_story_time_hints.py

@@ -0,0 +1,87 @@
+"""人生时间键与章节排序键（纯函数）。"""
+
+from datetime import datetime, timezone
+
+from app.agents.memoir.prompts import (
+    NARRATIVE_MERGE_EXISTING_MAX_CHARS,
+    clip_existing_story_body_for_merge,
+)
+from app.features.story.time_hints import (
+    infer_story_time_start,
+    life_sort_key_parts,
+    parse_time_start_year,
+    parse_year_from_title,
+)
+
+
+def test_parse_year_from_title() -> None:
+    assert parse_year_from_title("1999年 · 小学往事") == 1999
+    assert parse_year_from_title("2005 · 标题") == 2005
+    assert parse_year_from_title("无年份标题") is None
+
+
+def test_parse_time_start_year() -> None:
+    assert parse_time_start_year("1999") == 1999
+    assert parse_time_start_year("1999-03") == 1999
+    assert parse_time_start_year(None) is None
+
+
+def test_infer_story_time_start_prefers_existing() -> None:
+    assert (
+        infer_story_time_start(
+            title="2010 · x",
+            canonical_markdown="",
+            existing_time_start="2001",
+        )
+        == "2001"
+    )
+
+
+def test_infer_story_time_start_from_title() -> None:
+    assert (
+        infer_story_time_start(
+            title="2008年 · 某件事",
+            canonical_markdown="正文没有年份",
+            existing_time_start=None,
+        )
+        == "2008"
+    )
+
+
+def test_infer_story_time_start_from_body() -> None:
+    assert (
+        infer_story_time_start(
+            title="无年标题",
+            canonical_markdown="那是2012年的夏天。",
+            existing_time_start=None,
+        )
+        == "2012"
+    )
+
+
+def test_clip_existing_story_body_for_merge_truncates() -> None:
+    short = "a" * 100
+    assert clip_existing_story_body_for_merge(short) == short
+    long = "b" * (NARRATIVE_MERGE_EXISTING_MAX_CHARS + 50)
+    clipped = clip_existing_story_body_for_merge(long)
+    assert "省略" in clipped
+    # 头+尾+提示语可能略长于原串若干字节，但应远小于未截断的线性增长
+    assert len(clipped) <= len(long) + 400
+
+
+def test_life_sort_key_parts_order() -> None:
+    t0 = datetime(2020, 1, 1, tzinfo=timezone.utc)
+    t1 = datetime(2021, 1, 1, tzinfo=timezone.utc)
+    a = life_sort_key_parts(
+        time_start="1999",
+        title=None,
+        created_at=t1,
+        story_id="b",
+    )
+    b = life_sort_key_parts(
+        time_start="2005",
+        title=None,
+        created_at=t0,
+        story_id="a",
+    )
+    assert a < b