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/app/agents/memoir/narrative_agent.py

@@ -1,18 +1,21 @@
 """
 NarrativeAgent：生成创意标题和叙事改写。
-对应现有逻辑：get_creative_title_prompt、get_narrative_prompt
+对应现有逻辑：get_creative_title_json_prompt、get_narrative_json_prompt
 """
 
 from __future__ import annotations
 
+import json
 from typing import Any, Dict, Optional
 
 from app.agents.memoir.prompts import (
-    get_creative_title_prompt,
+    get_creative_title_json_prompt,
     get_narrative_json_prompt,
+    get_narrative_merge_json_prompt,
 )
-from app.core.langchain_llm import bind_json_object_mode
+from app.core.langchain_llm import invoke_json_object
 from app.core.logging import get_logger
+from app.features.memoir.memoir_images.json_payload import extract_json_payload
 
 logger = get_logger(__name__)
 
@@ -33,17 +36,26 @@ class NarrativeAgent:
         if not llm:
             return f"{stage} 回忆"
         try:
-            prompt = get_creative_title_prompt(
+            prompt = get_creative_title_json_prompt(
                 stage=stage,
                 emotion=emotion,
                 slots=slots,
                 user_profile=user_profile,
                 birth_year=birth_year,
             )
-            response = llm.invoke(prompt)
-            return (response.content or "").strip().strip('"')
+            raw = invoke_json_object(
+                llm,
+                prompt,
+                max_tokens=256,
+                agent="NarrativeAgent.generate_title",
+            )
+            data = json.loads(extract_json_payload(raw))
+            title = (data.get("title") or "").strip() if isinstance(data, dict) else ""
+            if title:
+                return title.strip('"')
+            return f"{stage} 回忆"
         except Exception as e:
-            logger.warning("NarrativeAgent 生成标题失败: %s", e)
+            logger.warning("NarrativeAgent 生成标题失败: {}", e)
             return f"{stage} 回忆"
 
     def generate_narrative(
@@ -56,25 +68,46 @@ class NarrativeAgent:
         birth_year: Optional[int] = None,
         llm: Any = None,
     ) -> str:
-        """将新对话改写为叙述。若无 LLM 则直接拼接"""
+        """将新对话改写为叙述。若无 LLM 则直接拼接。
+
+        若 `existing_content` 非空（append 路径），使用整篇合并提示，输出覆盖全篇的有序段落。
+        """
         if not llm:
             if existing_content:
                 return f"{existing_content}\n\n{new_content}"
             return new_content
         try:
-            prompt = get_narrative_json_prompt(
-                stage=stage,
-                slots=slots,
-                new_content=new_content,
-                existing_content=existing_content,
-                user_profile=user_profile,
-                birth_year=birth_year,
-            )
-            json_llm = bind_json_object_mode(llm, max_tokens=4096)
-            response = json_llm.invoke(prompt)
-            return (response.content or "").strip()
+            merge_mode = bool((existing_content or "").strip())
+            if merge_mode:
+                prompt = get_narrative_merge_json_prompt(
+                    stage=stage,
+                    slots=slots,
+                    new_content=new_content,
+                    existing_content=existing_content,
+                    user_profile=user_profile,
+                    birth_year=birth_year,
+                )
+                max_tokens = 8192
+                agent_name = "NarrativeAgent.generate_narrative_merge"
+            else:
+                prompt = get_narrative_json_prompt(
+                    stage=stage,
+                    slots=slots,
+                    new_content=new_content,
+                    existing_content=existing_content,
+                    user_profile=user_profile,
+                    birth_year=birth_year,
+                )
+                max_tokens = 4096
+                agent_name = "NarrativeAgent.generate_narrative"
+            return invoke_json_object(
+                llm,
+                prompt,
+                max_tokens=max_tokens,
+                agent=agent_name,
+            ).strip()
         except Exception as e:
-            logger.warning("NarrativeAgent 生成叙事失败: %s", e)
+            logger.warning("NarrativeAgent 生成叙事失败: {}", e)
             if existing_content:
                 return f"{existing_content}\n\n{new_content}"
             return new_content