fix:

1. 修复安卓部分机型顶部安全区遮挡回忆录标题的问题；
2. 降低封面图生成阈值和展示逻辑，独立封面图未生成时，使用正文图；
3. 去掉“嗯。”生硬回答，去掉不合理段首承接词；
4. 新增章节封面所需最少插图数的配置项

api/tests/test_cover_eligibility_effective_markdown.py

@@ -0,0 +1,54 @@
+"""封面闸门：canonical 未落库时须用物化正文计数 asset://。"""
+
+from unittest.mock import MagicMock, patch
+
+from app.features.memoir.cover_eligibility import (
+    chapter_eligible_for_cover_by_inline_body_image_count,
+    chapter_needs_cover_enqueue,
+    count_chapter_inline_body_images,
+    effective_chapter_markdown_for_cover_gates,
+)
+
+
+def test_effective_markdown_falls_back_to_materialize_when_canonical_empty() -> None:
+    ch = MagicMock()
+    ch.canonical_markdown = ""
+    ch.story_links = [MagicMock()]
+    with patch(
+        "app.features.memoir.chapter_markdown_compose.materialize_chapter_markdown_from_loaded_chapter",
+        return_value="正文\n\n![x](asset://a1)",
+    ):
+        assert "asset://" in effective_chapter_markdown_for_cover_gates(ch)
+
+
+def test_count_uses_effective_when_canonical_empty() -> None:
+    ch = MagicMock()
+    ch.canonical_markdown = ""
+    ch.story_links = [MagicMock()]
+    with patch(
+        "app.features.memoir.chapter_markdown_compose.materialize_chapter_markdown_from_loaded_chapter",
+        return_value="![alt](asset://id1)",
+    ):
+        assert count_chapter_inline_body_images(ch) == 1
+
+
+def test_eligible_with_explicit_markdown_override() -> None:
+    ch = MagicMock()
+    ch.canonical_markdown = ""
+    assert chapter_eligible_for_cover_by_inline_body_image_count(
+        ch, markdown="![a](asset://x)"
+    )
+
+
+def test_needs_cover_enqueue_uses_materialized_body() -> None:
+    ch = MagicMock()
+    ch.canonical_markdown = ""
+    ch.cover_asset_id = None
+    ch.story_links = [MagicMock(story=MagicMock())]
+    link = ch.story_links[0]
+    link.story = MagicMock()
+    with patch(
+        "app.features.memoir.chapter_markdown_compose.materialize_chapter_markdown_from_loaded_chapter",
+        return_value="故事\n\n![a](asset://z)",
+    ):
+        assert chapter_needs_cover_enqueue(ch) is True