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/features/memoir/memoir_images/prompting.py

@@ -2,7 +2,7 @@ import json
 import re
 from typing import Any, Optional
 
-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 .json_payload import extract_json_payload
@@ -61,13 +61,18 @@ class MemoirImagePromptService:
         if self.llm:
             raw_response = None
             try:
-                json_llm = bind_json_object_mode(self.llm, max_tokens=512)
-                response = json_llm.invoke(
+                prompt_text = (
                     "Return JSON only with keys prompt, style, size. "
-                    "Convert the memoir scene into an image-generation prompt.\n"
+                    "Convert the memoir scene into an image-generation prompt. "
+                    "The API uses response_format=json_object.\n"
                     + json.dumps(llm_input, ensure_ascii=False)
                 )
-                raw_response = response.content
+                raw_response = invoke_json_object(
+                    self.llm,
+                    prompt_text,
+                    max_tokens=512,
+                    agent="MemoirImagePromptService.build_prompt",
+                )
                 parsed = json.loads(extract_json_payload(raw_response))
                 return {
                     "prompt": _ensure_style_in_prompt(
@@ -79,7 +84,7 @@ class MemoirImagePromptService:
                 }
             except Exception as exc:
                 logger.warning(
-                    "图片 prompt 生成回退到默认模板: chapter_category=%s, title=%s, error=%s",
+                    "图片 prompt 生成回退到默认模板: chapter_category={}, title={}, error={}",
                     chapter_category,
                     chapter_title,
                     exc,
@@ -122,14 +127,20 @@ class MemoirImagePromptService:
 
         if self.llm:
             try:
-                json_llm = bind_json_object_mode(self.llm, max_tokens=512)
-                response = json_llm.invoke(
+                prompt_text = (
                     "Return JSON only with keys prompt, style, size. "
                     "Create an image-generation prompt for a memoir chapter COVER. "
-                    "Emphasize: hero composition, evocative scene, chapter cover aesthetic.\n"
+                    "Emphasize: hero composition, evocative scene, chapter cover aesthetic. "
+                    "The API uses response_format=json_object.\n"
                     + json.dumps(llm_input, ensure_ascii=False)
                 )
-                parsed = json.loads(extract_json_payload(response.content))
+                raw = invoke_json_object(
+                    self.llm,
+                    prompt_text,
+                    max_tokens=512,
+                    agent="MemoirImagePromptService.build_cover_prompt",
+                )
+                parsed = json.loads(extract_json_payload(raw))
                 return {
                     "prompt": _ensure_style_in_prompt(
                         parsed["prompt"], parsed.get("style", style)
@@ -140,7 +151,7 @@ class MemoirImagePromptService:
                 }
             except Exception as exc:
                 logger.warning(
-                    "封面 prompt 生成回退到默认模板: chapter_category=%s, title=%s, error=%s",
+                    "封面 prompt 生成回退到默认模板: chapter_category={}, title={}, error={}",
                     chapter_category,
                     chapter_title,
                     exc,