重构回忆录为 story-first / markdown-first 架构并整合图片意图与前端 UI 修复

本次 squash merge 将 codex-story-first-image-intent 的整体改动合入 development，核心内容包括：

1. 后端数据与迁移：新增 stories、story_versions、story_image_intents、chapter_cover_intents、assets 等模型与 Alembic 迁移，建立 story-first、markdown-first、asset-first 的主数据链路。

2. 生成与任务链：引入 StoryBuilderOrchestrator、ChapterComposerOrchestrator、story_image_tasks、chapter_cover_tasks，图片生成从正文占位符改为结构化 intent -> asset -> markdown 回填。

3. 并发与一致性：为 story/chapter intent 增加 claim_token、claimed_at、attempt_count，采用数据库原子 claim 为主、Redis 锁为辅，避免重复生成、锁误删和 processing 卡死。

4. Memoir 读写路径：章节 canonical_markdown 成为正文真源，列表/详情接口补齐 markdown、cover_asset、word_count 等字段，PDF 与 asset 解析链路同步升级。

5. Memory / Retrieval：扩展 transcript ingest、chunking、evidence 检索与 story 聚合基础设施，为后续 story-first RAG 与多 agent 编排提供底座。

6. App 端体验：章节页继续走 MarkdownRenderer 阅读链，同时吸收 fix3-19 的跨平台 UI glitch 修复；更新对话页、首页、文案资源与章节列表映射逻辑。

7. 测试与文档：补充 asset resolver、story image task、章节封面派发、markdown 映射等回归测试，并加入图片占位符退役设计文档。

api/app/features/memoir/service.py

@@ -1,6 +1,5 @@
 """Memoir service — 回忆录编排（章节生成、状态流转）；通过 MemoryService 获取 evidence。"""
 
-import uuid
 from datetime import datetime, timezone
 from typing import List, Optional
 
@@ -16,14 +15,18 @@ from app.agents.memoir.prompts import (
     STAGE_TO_ORDER,
 )
 from app.features.memoir import repo
+from app.features.memoir.asset_resolver import (
+    collect_asset_ids_for_chapter,
+    collect_asset_ids_for_chapters,
+    strip_legacy_image_placeholders,
+)
+from app.features.memoir.asset_urls import signed_urls_for_asset_ids
 from app.features.memoir.helpers import (
     chapter_to_dict,
+    chapter_to_list_dict,
     is_image_permanently_unavailable,
 )
-from app.features.memoir.models import Book, Chapter, ChapterSection, MemoirImage
-from app.features.memoir.memoir_images.parser import build_initial_image_assets
-from app.features.memoir.memoir_images.serializers import image_dict_to_row_kwargs
-from app.features.memoir.memoir_images.prompting import MemoirImagePromptService
+from app.features.memoir.models import Book, Chapter, ChapterSection
 from app.features.memoir.memoir_images.settings import MemoirImageSettings
 from app.features.memory.service import MemoryService
 
@@ -121,12 +124,19 @@ class MemoirService:
         stmt = (
             select(Chapter)
             .where(Chapter.user_id == user_id, Chapter.is_active == True)
-            .options(joinedload(Chapter.sections))
+            .options(
+                joinedload(Chapter.sections).joinedload(ChapterSection.image_record),
+                joinedload(Chapter.images),
+            )
             .order_by(Chapter.order_index)
         )
         result = await self._db.execute(stmt)
         chapters = list(result.unique().scalars().all())
-        pdf_bytes = await pdf_service.generate_pdf(book, chapters)
+        asset_ids = collect_asset_ids_for_chapters(chapters)
+        asset_map = await signed_urls_for_asset_ids(self._db, asset_ids)
+        pdf_bytes = await pdf_service.generate_pdf(
+            book, chapters, asset_url_map=asset_map
+        )
         return {
             "pdf_base64": pdf_bytes.decode("latin1"),
             "filename": f"{book.title}.pdf",
@@ -138,6 +148,10 @@ class MemoirService:
         chapters = await repo.get_chapters_with_sections(
             user_id, self._db, is_new_only=is_new
         )
+        asset_ids: set[str] = set()
+        for ch in chapters:
+            asset_ids |= collect_asset_ids_for_chapter(ch)
+        asset_map = await signed_urls_for_asset_ids(self._db, asset_ids)
         chapter_by_category: dict[str, Chapter] = {}
         for ch in chapters:
             if ch.category and ch.category not in chapter_by_category:
@@ -147,7 +161,7 @@ class MemoirService:
             ch = chapter_by_category.pop(category, None)
             if ch:
                 await self._cleanup_unavailable_images(ch)
-                all_chapters.append(chapter_to_dict(ch))
+                all_chapters.append(chapter_to_list_dict(ch, asset_url_map=asset_map))
             else:
                 if is_new is True:
                     continue
@@ -155,13 +169,17 @@ class MemoirService:
                     {
                         "id": f"placeholder_{category}",
                         "title": CHAPTER_CATEGORIES[category],
-                        "content": "",
+                        "category": category,
                         "order_index": STAGE_TO_ORDER.get(category, 999),
                         "status": "empty",
-                        "category": category,
-                        "images": [],
+                        "summary": "",
+                        "canonical_markdown": "",
+                        "content": "",
+                        "cover_asset": None,
                         "cover_image": None,
+                        "images": [],
                         "sections": [],
+                        "word_count": 0,
                         "updated_at": None,
                         "is_new": False,
                         "source_segments": [],
@@ -169,7 +187,7 @@ class MemoirService:
                 )
         for ch in chapter_by_category.values():
             await self._cleanup_unavailable_images(ch)
-            all_chapters.append(chapter_to_dict(ch))
+            all_chapters.append(chapter_to_list_dict(ch, asset_url_map=asset_map))
         return all_chapters
 
     async def get_chapter(self, chapter_id: str, user_id: str) -> dict:
@@ -181,7 +199,10 @@ class MemoirService:
         if not chapter.is_active:
             raise HTTPException(status_code=404, detail="Chapter not found")
         await self._cleanup_unavailable_images(chapter)
-        return chapter_to_dict(chapter)
+        asset_map = await signed_urls_for_asset_ids(
+            self._db, collect_asset_ids_for_chapter(chapter)
+        )
+        return chapter_to_dict(chapter, asset_url_map=asset_map)
 
     async def disable_chapter(self, chapter_id: str, user_id: str) -> dict:
         chapter = await self._db.get(Chapter, chapter_id)
@@ -220,10 +241,14 @@ class MemoirService:
 
     async def check_and_trigger_cover_generation(self, user_id: str) -> dict:
         """
-        检查可生成封面的章节（section 配图 > 3 且无已完成封面），
-        若有则触发生成任务。已有封面的章节不再检查。
+        有正文、尚无 cover_asset、且 legacy 封面 MemoirImage 未 completed 时，
+        派发 generate_chapter_cover（由 intent/asset 闭环完成）。
         """
-        from app.tasks.memoir_tasks import generate_chapter_images
+        from app.tasks.chapter_cover_tasks import generate_chapter_cover
+
+        img_settings = MemoirImageSettings.from_env()
+        if not img_settings.enabled:
+            return {"triggered": []}
 
         chapters = await repo.get_chapters_with_sections(
             user_id, self._db, active_only=True, is_new_only=None
@@ -232,59 +257,33 @@ class MemoirService:
         for ch in chapters:
             if not ch.category or ch.status == "empty":
                 continue
-            sections = getattr(ch, "sections", None) or []
-            section_image_count = sum(
-                1 for s in sections if getattr(s, "image_id", None)
+            if getattr(ch, "cover_asset_id", None):
+                continue
+            md = (ch.canonical_markdown or "").strip()
+            section_blob = "\n\n".join(
+                (s.content or "").strip()
+                for s in getattr(ch, "sections", None) or []
+                if (s.content or "").strip()
             )
+            body = md or strip_legacy_image_placeholders(section_blob).strip()
+            if not body:
+                continue
             images = getattr(ch, "images", None) or []
             cover_rec = next(
                 (m for m in images if getattr(m, "section_id", None) is None),
                 None,
             )
-            if section_image_count <= 3:
-                continue
             if (
                 cover_rec
                 and (getattr(cover_rec, "status") or "").strip() == "completed"
             ):
                 continue
-            if cover_rec is None:
-                img_settings = MemoirImageSettings.from_env()
-                if img_settings.enabled:
-                    now_iso = datetime.now(timezone.utc).isoformat()
-                    cover_ph = {
-                        "placeholder": "{{{{{{{{IMAGE:章节封面}}}}}}}}",
-                        "description": "章节封面",
-                        "index": 0,
-                    }
-                    style = MemoirImagePromptService.CATEGORY_STYLE_MAP.get(
-                        ch.category or "", img_settings.default_style
-                    )
-                    cover_asset = build_initial_image_assets(
-                        [cover_ph],
-                        img_settings.provider,
-                        style,
-                        img_settings.default_size,
-                        now_iso,
-                    )[0]
-                    kwargs = image_dict_to_row_kwargs(cover_asset)
-                    cover_mi = MemoirImage(
-                        id=str(uuid.uuid4()).replace("-", "")[:32],
-                        chapter_id=ch.id,
-                        section_id=None,
-                        order_index=0,
-                        **kwargs,
-                    )
-                    self._db.add(cover_mi)
-                    await self._db.commit()
-                    await self._db.refresh(ch)
-                    logger.info("创建封面占位: chapter=%s", ch.id)
             try:
-                generate_chapter_images.delay(ch.id)
+                generate_chapter_cover.delay(ch.id)
                 triggered.append(ch.id)
-                logger.info("触发生成封面: chapter=%s", ch.id)
+                logger.info("触发生成章节封面(asset): chapter=%s", ch.id)
             except Exception as exc:
-                logger.warning("封面生成任务派发失败: chapter=%s, error=%s", ch.id, exc)
+                logger.warning("封面任务派发失败: chapter=%s, error=%s", ch.id, exc)
         return {"triggered": triggered}
 
     async def mark_memoir_read(self, user_id: str) -> dict: