fix(parser): 修复 Docling 图片异常占位回填

保留上传失败的图片占位说明，并补充混合图片类型回填顺序的回归测试，避免占位符错位或异常路径掩盖原始错误。

Taskr: 2026-05-12-fix-docling-image-replacement-regression

backend/package/yuxi/plugins/parser/unified.py

@@ -131,6 +131,7 @@ def _convert_with_docling(file_path: Path, params: dict | None = None) -> str:
         for pic in doc.pictures:
             uri = str(pic.image.uri) if hasattr(pic, "image") and hasattr(pic.image, "uri") else ""
             if uri.startswith("data:"):
+                filename = "image"
                 try:
                     image_data, mime_type = _parse_data_uri(uri)
                     filename = f"image_{int(time.time() * 1000000)}.{mime_type.split('/')[-1]}"
@@ -138,7 +139,7 @@ def _convert_with_docling(file_path: Path, params: dict | None = None) -> str:
                     replacements.append(f"![{filename}]({url})")
                 except Exception as e:  # noqa: BLE001
                     logger.error(f"上传图片失败 {filename}: {e}")
-                    replacements.append("")
+                    replacements.append(f"[图片: {filename}]")
             else:
                 replacements.append("")
 

backend/test/unit/plugins/test_parser_facade.py

@@ -76,9 +76,10 @@ def test_convert_with_docling_reinserts_image_links_in_document_order(
     fake_doc = SimpleNamespace(
         pictures=[
             SimpleNamespace(image=SimpleNamespace(uri=f"data:image/png;base64,{first_image}")),
+            SimpleNamespace(image=SimpleNamespace(uri="https://example.test/remote.png")),
             SimpleNamespace(image=SimpleNamespace(uri=f"data:image/png;base64,{second_image}")),
         ],
-        export_to_markdown=lambda: "before\n<!-- image -->\nbetween\n<!-- image -->\nafter",
+        export_to_markdown=lambda: "before\n<!-- image -->\nremote\n<!-- image -->\nbetween\n<!-- image -->\nafter",
     )
     fake_result = SimpleNamespace(status=SimpleNamespace(name="SUCCESS"), document=fake_doc)
     uploaded_images: list[bytes] = []
@@ -103,12 +104,44 @@ def test_convert_with_docling_reinserts_image_links_in_document_order(
     assert markdown == (
         "before\n"
         "![image_1000000.png](https://example.test/1.png)\n"
+        "remote\n"
+        "\n"
         "between\n"
         "![image_2000000.png](https://example.test/2.png)\n"
         "after"
     )
 
 
+def test_convert_with_docling_keeps_image_placeholder_when_upload_fails(
+    tmp_path: Path,
+    monkeypatch: pytest.MonkeyPatch,
+):
+    file_path = tmp_path / "parser_test.docx"
+    file_path.write_bytes(b"fake docx")
+    image = base64.b64encode(b"image data").decode()
+    fake_doc = SimpleNamespace(
+        pictures=[SimpleNamespace(image=SimpleNamespace(uri=f"data:image/png;base64,{image}"))],
+        export_to_markdown=lambda: "before\n<!-- image -->\nafter",
+    )
+    fake_result = SimpleNamespace(status=SimpleNamespace(name="SUCCESS"), document=fake_doc)
+
+    class FakeConverter:
+        def convert(self, path: Path):
+            assert path == file_path
+            return fake_result
+
+    def _raise_upload_error(*args, **kwargs):
+        raise RuntimeError("upload failed")
+
+    monkeypatch.setattr(parser_unified, "_get_docling_converter", lambda: FakeConverter())
+    monkeypatch.setattr(parser_unified, "_upload_image_to_minio", _raise_upload_error)
+    monkeypatch.setattr(parser_unified.time, "time", lambda: 1.0)
+
+    markdown = parser_unified._convert_with_docling(file_path)
+
+    assert markdown == "before\n[图片: image_1000000.png]\nafter"
+
+
 def test_parser_parse_png_file_returns_markdown_text_with_mocked_ocr(
     tmp_path: Path,
     monkeypatch: pytest.MonkeyPatch,