feat(api): 叙事 prompt、职业上下文、读路径章节、WS 解耦与错误脱敏

- 回忆录：事实边界补充允许清单；传记文体示例与 JSON 叙事要求对齐
- default 职业提示 occupation_context；cadre/military 退休语境
- GET 章节读路径零写入，prepare_chapter_read_view + markdown_for_response
- 文本归一抽到 core/text_normalize；移除弃用 reply 策略与 recompose_chapters_for_story
- ConversationService：WS 连接/用户段落/结束对话；对外错误固定文案
- 测试：HTTP 脱敏契约、章节读视图、occupation 与 background_voice

api/app/features/memoir/helpers.py

@@ -95,6 +95,8 @@ def chapter_cover_to_dict(
     if not chapter_eligible_for_cover_by_inline_body_image_count(ch):
         return None
     m = primary_chapter_memoir_image(ch)
+    if m and is_image_permanently_unavailable(m):
+        m = None
     if m:
         return memoir_image_to_dict(m)
     asset_url_map = asset_url_map or {}
@@ -120,8 +122,10 @@ def chapter_cover_to_dict(
     return None
 
 
-def _chapter_markdown(ch: Chapter) -> str:
-    """正文真源：canonical_markdown。"""
+def _chapter_markdown(ch: Chapter, *, override: str | None = None) -> str:
+    """正文：优先读路径临时物化串，否则 canonical_markdown。"""
+    if override is not None and str(override).strip():
+        return str(override).strip()
     md = getattr(ch, "canonical_markdown", None)
     if md and str(md).strip():
         return str(md).strip()
@@ -129,12 +133,15 @@ def _chapter_markdown(ch: Chapter) -> str:
 
 
 def chapter_to_list_dict(
-    ch: Chapter, asset_url_map: dict[str, str] | None = None
+    ch: Chapter,
+    asset_url_map: dict[str, str] | None = None,
+    *,
+    markdown_for_response: str | None = None,
 ) -> dict:
     """列表视图：与详情字段对齐的最小子集。"""
     cover = chapter_cover_to_dict(ch, asset_url_map=asset_url_map)
     cover_normalized = first_normalized_image_for_api(cover)
-    canonical_raw = _chapter_markdown(ch)
+    canonical_raw = _chapter_markdown(ch, override=markdown_for_response)
     wcount = len(canonical_raw.strip()) if canonical_raw else 0
     return {
         "id": ch.id,
@@ -153,7 +160,12 @@ def chapter_to_list_dict(
     }
 
 
-def chapter_to_dict(ch: Chapter, asset_url_map: dict[str, str] | None = None) -> dict:
+def chapter_to_dict(
+    ch: Chapter,
+    asset_url_map: dict[str, str] | None = None,
+    *,
+    markdown_for_response: str | None = None,
+) -> dict:
     """详情视图：stories-first 契约。asset_url_map 用于解析 asset:// 与 cover_asset_id。"""
     asset_url_map = asset_url_map or {}
     resolve = lambda aid: asset_url_map.get(aid)  # noqa: E731
@@ -161,7 +173,7 @@ def chapter_to_dict(ch: Chapter, asset_url_map: dict[str, str] | None = None) ->
     cover = chapter_cover_to_dict(ch, asset_url_map=asset_url_map)
     cover_normalized = first_normalized_image_for_api(cover)
     # 正文真源：优先 canonical_markdown
-    canonical_md = _chapter_markdown(ch)
+    canonical_md = _chapter_markdown(ch, override=markdown_for_response)
     canonical_md = resolve_asset_refs_in_markdown(canonical_md, resolve)
     reading_segments = resolve_reading_segments_for_chapter_detail(
         ch, asset_url_map=asset_url_map