feat(api): embed memoir chapter images in PDF export and strip placeholders

Made-with: Cursor

api/tests/test_pdf_service_images.py

@@ -0,0 +1,46 @@
+import unittest
+from unittest.mock import AsyncMock, patch, MagicMock
+
+from api.services.pdf_service import PDFService
+
+
+class PDFServiceImagesTest(unittest.IsolatedAsyncioTestCase):
+    @patch("api.services.pdf_service.httpx.AsyncClient")
+    async def test_generate_pdf_embeds_completed_images_and_removes_placeholders(self, async_client_cls):
+        png_bytes = (
+            b"\x89PNG\r\n\x1a\n\x00\x00\x00\rIHDR\x00\x00\x00\x01\x00\x00\x00\x01"
+            b"\x08\x02\x00\x00\x00\x90wS\xde\x00\x00\x00\x0cIDATx\x9cc```\x00\x00"
+            b"\x00\x04\x00\x01\xf6\x178U\x00\x00\x00\x00IEND\xaeB`\x82"
+        )
+        mock_response = MagicMock()
+        mock_response.content = png_bytes
+        mock_response.raise_for_status = MagicMock()
+
+        mock_client = AsyncMock()
+        mock_client.get.return_value = mock_response
+        async_client_cls.return_value.__aenter__ = AsyncMock(return_value=mock_client)
+        async_client_cls.return_value.__aexit__ = AsyncMock(return_value=False)
+
+        service = PDFService()
+        book = type("BookStub", (), {"title": "我的回忆录"})()
+        chapter = type(
+            "ChapterStub",
+            (),
+            {
+                "title": "童年的夏天",
+                "content": "那条路我一直记得。\n\n{{{{IMAGE:南方小镇的青石板路}}}}\n\n奶奶常坐在那里。",
+                "images": [
+                    {
+                        "index": 0,
+                        "placeholder": "{{{{IMAGE:南方小镇的青石板路}}}}",
+                        "url": "https://cos.example.com/0.png",
+                        "status": "completed",
+                    }
+                ],
+            },
+        )()
+
+        pdf_bytes = await service.generate_pdf(book, [chapter])
+
+        self.assertGreater(len(pdf_bytes), 100)
+        self.assertNotIn(b"IMAGE:", pdf_bytes)