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/scripts/migrate_chapters_to_sections.py

@@ -0,0 +1,98 @@
+"""
+将 chapters 的 content + images 迁移到 chapter_sections，并删除 chapters.content / chapters.images。
+
+前置：已执行 api/migrations/add_chapter_sections.sql（创建 chapter_sections 表、chapters.cover_image 列）。
+
+用法（在 api 目录下）:
+    python -m scripts.migrate_chapters_to_sections
+"""
+import json
+import logging
+import os
+import sys
+import uuid
+
+sys.path.insert(0, os.path.dirname(os.path.dirname(os.path.abspath(__file__))))
+
+from sqlalchemy import text
+from database.database import engine
+from services.memoir_images.parser import split_narrative_to_sections
+
+logging.basicConfig(level=logging.INFO, format="%(message)s")
+logger = logging.getLogger(__name__)
+
+
+def run():
+    with engine.connect() as conn:
+        # 检查是否还存在 content 列（若已删则跳过）
+        r = conn.execute(text("""
+            SELECT column_name FROM information_schema.columns
+            WHERE table_schema = 'public' AND table_name = 'chapters' AND column_name = 'content'
+        """))
+        if r.fetchone() is None:
+            logger.info("chapters.content 已不存在，跳过迁移")
+            return
+
+        # 读取所有有 content 的章节（原始列）
+        rows = conn.execute(text("""
+            SELECT id, content, images FROM chapters WHERE content IS NOT NULL AND trim(content) != ''
+        """)).fetchall()
+
+        for row in rows:
+            ch_id, content, images_raw = row[0], row[1], row[2]
+            images = json.loads(images_raw) if isinstance(images_raw, str) else (images_raw or [])
+            if not isinstance(images, list):
+                images = []
+
+            sections = split_narrative_to_sections(content or "")
+            if not sections:
+                # 无占位符：整段为一条 section，无图
+                section_id = str(uuid.uuid4()).replace("-", "")[:32]
+                conn.execute(text("""
+                    INSERT INTO chapter_sections (id, chapter_id, order_index, content, image, updated_at)
+                    VALUES (:id, :ch_id, 0, :content, NULL, NOW())
+                """), {"id": section_id, "ch_id": ch_id, "content": (content or "").strip()})
+                conn.commit()
+                logger.info("章节 %s: 1 条 section（无图）", ch_id)
+                continue
+
+            first_cover = None
+            img_index = 0
+            for order_idx, seg in enumerate(sections):
+                section_id = str(uuid.uuid4()).replace("-", "")[:32]
+                seg_content = seg.get("content") or ""
+                ph = seg.get("placeholder_info")
+                image_json = None
+                if ph is not None and img_index < len(images):
+                    image_json = json.dumps(images[img_index]) if isinstance(images[img_index], dict) else None
+                    if first_cover is None and image_json:
+                        first_cover = image_json
+                    img_index += 1
+
+                conn.execute(text("""
+                    INSERT INTO chapter_sections (id, chapter_id, order_index, content, image, updated_at)
+                    VALUES (:id, :ch_id, :ord, :content, :img::jsonb, NOW())
+                """), {
+                    "id": section_id,
+                    "ch_id": ch_id,
+                    "ord": order_idx,
+                    "content": seg_content,
+                    "img": image_json,
+                })
+            if first_cover:
+                conn.execute(
+                    text("UPDATE chapters SET cover_image = :img::jsonb WHERE id = :id"),
+                    {"img": first_cover, "id": ch_id},
+                )
+            conn.commit()
+            logger.info("章节 %s: %d 条 sections", ch_id, len(sections))
+
+        # 删除 chapters.content 和 chapters.images
+        conn.execute(text("ALTER TABLE chapters DROP COLUMN IF EXISTS content"))
+        conn.execute(text("ALTER TABLE chapters DROP COLUMN IF EXISTS images"))
+        conn.commit()
+        logger.info("已删除 chapters.content 与 chapters.images")
+
+
+if __name__ == "__main__":
+    run()