feat(api): 拆分章节物化与 Story 后处理，并加固 Redis 锁与腾讯 ASR

回忆录 Story 流水线（同步）
- 同步路径仅写入 Story 与章节关联，改为 mark_chapter_dirty_sync，不再内联 compose
- 物化由 Celery recompose_chapter 异步完成；compose 不变量与异常时保留 dirty 的语义在 repo 中补充说明
- Evidence：大批次时降低 top_k；路由候选 story 携带 char_count/version_count；append 超长/版本过多时强制新开 story
- 叙事 prompt：relevant_chunks 去重，减少重复证据噪声
- 叙事回退与忠实度 gate：返回 fallback 类型并记录结构化日志（含耗时、JSON 有效性等）

Post-commit 与任务编排
- 新增 post_commit.enqueue_story_post_commit_effects：统一派发 generate_story_image（Redis 去重）、延迟 recompose_chapter、可选 memory compaction
- memoir_tasks / story_service / story_image_tasks 改为调用 post-commit 入口；主图回填后按关联章节重算并调度物化与 compacs（锁委托、Redis 单例、ASR to_thread）
- 更新 test_narrative_pipeline 以适配 _apply_narrative_fallbacks 返回值

api/app/tasks/story_image_tasks.py

@@ -31,27 +31,38 @@ STORY_IMAGE_LOCK_TTL_SECONDS = 1800
 STORY_IMAGE_CLAIM_TTL_SECONDS = 1800
 
 
-def _enqueue_chapter_recompose_for_story(story_id: str) -> None:
-    """story 正文因主图回填变更后，标记关联章节 dirty 并异步物化。"""
+def _enqueue_chapter_effects_after_image_backfill(story_id: str) -> None:
+    """主图回填后标记关联章节 dirty，并经统一 post-commit 入口派发章节物化与 compaction。"""
     try:
         with get_sync_db() as session:
             from app.features.memoir import repo as memoir_repo
 
+            story = session.get(Story, story_id)
+            if not story:
+                return
+            uid = str(story.user_id)
             memoir_repo.mark_chapters_dirty_for_story_sync(session, story_id)
+            chapter_ids = memoir_repo.get_chapter_ids_linked_to_story_sync(
+                session, story_id
+            )
             session.commit()
+            user_id = uid
     except Exception as exc:
         logger.warning(
             "mark_chapters_dirty_for_story_sync failed story={}: {}", story_id, exc
         )
         return
-    try:
-        from app.tasks.chapter_compose_tasks import recompose_chapters_for_story
+    from app.features.story.post_commit import enqueue_story_post_commit_effects
 
-        recompose_chapters_for_story.delay(story_id)
-    except Exception as exc:
-        logger.warning(
-            "recompose_chapters_for_story.delay failed story={}: {}", story_id, exc
-        )
+    enqueue_story_post_commit_effects(
+        user_id=user_id,
+        story_ids=set(),
+        chapter_ids=set(chapter_ids),
+        trigger_source="story_image_backfill",
+        need_image=False,
+        need_recompose=True,
+        need_compaction=True,
+    )
 
 
 def _build_story_image_cos_key(
@@ -320,7 +331,7 @@ def generate_story_image(self, story_id: str):
 
             db.commit()
 
-        _enqueue_chapter_recompose_for_story(story_id)
+        _enqueue_chapter_effects_after_image_backfill(story_id)
 
         logger.info(
             "generate_story_image: story={}, asset={}",