把“章节正文 + 图片”从 chapters 单表/JSON 结构，重构为“章节 chapter + 段落 section + 图片 memoir_images 独立表”的新数据模型，同时联动修改接口、PDF 导出、异步任务、迁移脚本、测试，以及修复 Android 端聊天列表显示问题。 (#9)

* refactor: 表结构重构，新增段落section和图片image新表

* fix: fix android app import error

* refactor: 重构文件名

* fix: 优化提示词

* fix: 消息气泡显示位置异常问题

---------

Co-authored-by: yangshilin <2157598560@qq.com>

api/services/pdf_service.py

@@ -13,6 +13,7 @@ from reportlab.lib.units import inch
 from reportlab.platypus import SimpleDocTemplate, Paragraph, Spacer, PageBreak, Image as ReportLabImage
 from reportlab.pdfbase import pdfmetrics
 from reportlab.pdfbase.cidfonts import UnicodeCIDFont
+from services.memoir_images.serializers import memoir_image_to_dict
 from services.memoir_images.parser import PLACEHOLDER_RE
 from services.memoir_images.schema import IMAGE_STATUS_COMPLETED, normalize_image_assets
 from services.memoir_images.storage import (
@@ -48,6 +49,28 @@ def split_content_blocks(content: str, images: list[dict]) -> list[dict]:
     return blocks
 
 
+def sections_to_blocks(sections: list, prepare_fn=None) -> list[dict]:
+    """
+    从 chapter_sections 生成 PDF 用的 blocks：按 order_index 顺序，每段正文 + 可选一张图。
+    prepare_fn(images) 用于解析签名 URL，默认 _prepare_pdf_image_assets。
+    """
+    if prepare_fn is None:
+        prepare_fn = _prepare_pdf_image_assets
+    blocks: list[dict] = []
+    for section in sorted(sections, key=lambda s: getattr(s, "order_index", 0)):
+        content = (getattr(section, "content", None) or "").strip()
+        if content:
+            blocks.append({"type": "text", "value": content})
+        img = None
+        if getattr(section, "image_record", None):
+            img = memoir_image_to_dict(section.image_record)
+        if img:
+            prepared = prepare_fn([img])
+            if prepared and prepared[0].get("url"):
+                blocks.append({"type": "image", "url": prepared[0]["url"]})
+    return blocks
+
+
 def _prepare_pdf_image_assets(images: list[dict]) -> list[dict]:
     storage = TencentCosStorageService.from_env()
     prepared_assets: list[dict] = []
@@ -148,8 +171,12 @@ class PDFService:
             story.append(Paragraph(chapter.title, heading_style))
             story.append(Spacer(1, 0.2 * inch))
 
-            images = _prepare_pdf_image_assets(getattr(chapter, "images", None) or [])
-            blocks = split_content_blocks(chapter.content, images)
+            sections = getattr(chapter, "sections", None) or []
+            if sections:
+                blocks = sections_to_blocks(sections)
+            else:
+                images = _prepare_pdf_image_assets(getattr(chapter, "images", None) or [])
+                blocks = split_content_blocks(getattr(chapter, "content", "") or "", images)
 
             for block in blocks:
                 if block["type"] == "text":