修复：CI 部署环境与 ref 错配、迁移碎片化、图片意图 source_span、章节物化脏版式、会话历史与本地语音不一致

新增：TTS 上传 COS 与分片、章节 reading_segments 物化与快照、markdown 清洗、会话消息 repository、语音 store 重构与相关测试

api/tests/test_story_backfill.py

@@ -0,0 +1,20 @@
+import unittest
+
+from app.features.story.backfill import backfill_image_into_markdown
+
+
+class StoryBackfillTest(unittest.TestCase):
+    def test_appends_image_at_end_with_prompt_brief_alt(self):
+        md = "第一段\n\n第二段"
+        out = backfill_image_into_markdown(md, "aid-1", "院子里的藤椅")
+        self.assertTrue(out.endswith("](asset://aid-1)\n"))
+        self.assertIn("第二段", out)
+        self.assertLess(out.index("第二段"), out.index("!["))
+
+    def test_empty_markdown_is_only_image_ref(self):
+        out = backfill_image_into_markdown("", "x", "提示")
+        self.assertEqual(out, "![提示](asset://x)")
+
+    def test_escapes_bracket_in_alt(self):
+        out = backfill_image_into_markdown("正文", "a", "说明]尾")
+        self.assertIn(r"说明\]", out)