feat(04-02): add content downloading and module export for DownloadProcessor

TDD GREEN phase:
- DownloadProcessor downloads article/answer/zhuanlan content
- Video content is skipped (handled by ASR in Phase 3)
- Content files saved with correct naming convention
- DownloadProcessor exported from kb_pipeline.processors
- All 17 tests pass

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

kb_pipeline/processors/__init__.py

@@ -3,11 +3,13 @@
 This module contains processors for various content transformation tasks:
 - BaseProcessor: Abstract base class for all processors
 - ParseProcessor: URL parsing for various platforms
+- DownloadProcessor: Metadata and content downloading
 - ASRProcessor: Audio-to-text conversion (subtitle download + Whisper.cpp)
 """
 
 from .base import BaseProcessor
 from .parse import ParseProcessor
+from .download import DownloadProcessor
 from .asr import ASRProcessor
 
-__all__ = ["BaseProcessor", "ParseProcessor", "ASRProcessor"]
+__all__ = ["BaseProcessor", "ParseProcessor", "DownloadProcessor", "ASRProcessor"]

tests/test_processors/test_download.py

@@ -321,3 +321,163 @@ class TestDownloadProcessorMetadata:
         call_args = mock_state.mark_step_failed.call_args
         assert call_args[0][0] == "download"  # step_name
         mock_state_manager.save.assert_called_once_with(mock_state)
+
+
+class TestDownloadProcessorContent:
+    """Tests for DownloadProcessor content downloading."""
+
+    @pytest.fixture
+    def mock_bilibili_article_adapter(self):
+        """Create a mock BilibiliAdapter for articles."""
+        adapter = MagicMock()
+        adapter.fetch_metadata = AsyncMock(return_value={
+            "title": "Test Article Title",
+            "author": "Test Author",
+            "cvid": "CV123",
+            "url": "https://www.bilibili.com/read/cv123",
+        })
+        adapter.fetch_content = AsyncMock(return_value="---\ntitle: Test Article\n---\nArticle content here")
+        adapter.get_output_filename = MagicMock(side_effect=lambda cid, ctype, suffix: f"bilibili_{cid}_{suffix}")
+        return adapter
+
+    @pytest.fixture
+    def mock_bilibili_video_adapter(self):
+        """Create a mock BilibiliAdapter for videos."""
+        adapter = MagicMock()
+        adapter.fetch_metadata = AsyncMock(return_value={
+            "metadata": {
+                "title": "Test Video Title",
+                "mid": 12345,
+                "bvid": "BV1xx",
+                "duration": 300,
+            },
+            "stats": {"view": 1000},
+        })
+        adapter.get_output_filename = MagicMock(side_effect=lambda cid, ctype, suffix: f"bilibili_{cid}_{suffix}")
+        return adapter
+
+    @pytest.fixture
+    def mock_state_manager(self):
+        """Create a mock WorkflowStateManager."""
+        manager = MagicMock()
+        manager.load = MagicMock(return_value=None)
+        manager.save = MagicMock()
+        return manager
+
+    @pytest.mark.asyncio
+    async def test_content_downloads_article_content(
+        self, mock_bilibili_article_adapter, mock_state_manager, tmp_path
+    ):
+        """Test 1: DownloadProcessor downloads Bilibili article content"""
+        from kb_pipeline.processors.download import DownloadProcessor
+        from kb_pipeline.schemas import DownloadInput
+
+        input_data = DownloadInput(
+            content_id="CV123",
+            platform="bilibili",
+            content_dir=str(tmp_path),
+            content_type="article"
+        )
+
+        with patch("kb_pipeline.processors.base.get_settings") as mock_settings:
+            mock_settings.return_value = MagicMock()
+            with patch.object(
+                DownloadProcessor, '_get_adapter', return_value=mock_bilibili_article_adapter
+            ):
+                processor = DownloadProcessor(state_manager=mock_state_manager)
+                result = await processor.process(input_data)
+
+        assert result.success is True
+        assert result.content_file != ""  # Content should be downloaded
+        assert "bilibili_CV123_content.md" in result.content_file
+
+        # Verify content file was created
+        content_path = Path(result.content_file)
+        assert content_path.exists()
+
+        # Verify fetch_content was called
+        mock_bilibili_article_adapter.fetch_content.assert_called_once_with("CV123", "article")
+
+    @pytest.mark.asyncio
+    async def test_content_skips_video_download(
+        self, mock_bilibili_video_adapter, mock_state_manager, tmp_path
+    ):
+        """Test 2: DownloadProcessor skips video download (handled by ASR)"""
+        from kb_pipeline.processors.download import DownloadProcessor
+        from kb_pipeline.schemas import DownloadInput
+
+        input_data = DownloadInput(
+            content_id="BV1xx",
+            platform="bilibili",
+            content_dir=str(tmp_path),
+            content_type="video"
+        )
+
+        with patch("kb_pipeline.processors.base.get_settings") as mock_settings:
+            mock_settings.return_value = MagicMock()
+            with patch.object(
+                DownloadProcessor, '_get_adapter', return_value=mock_bilibili_video_adapter
+            ):
+                processor = DownloadProcessor(state_manager=mock_state_manager)
+                result = await processor.process(input_data)
+
+        assert result.success is True
+        assert result.content_file == ""  # Video content not downloaded (handled by ASR)
+        assert result.duration == 300  # Duration should be extracted
+
+        # Verify fetch_content was NOT called for video
+        mock_bilibili_video_adapter.fetch_content.assert_not_called()
+
+    @pytest.mark.asyncio
+    async def test_content_creates_correct_output_file_paths(
+        self, mock_bilibili_article_adapter, mock_state_manager, tmp_path
+    ):
+        """Test 3: DownloadProcessor creates correct output file paths"""
+        from kb_pipeline.processors.download import DownloadProcessor
+        from kb_pipeline.schemas import DownloadInput
+
+        input_data = DownloadInput(
+            content_id="CV123",
+            platform="bilibili",
+            content_dir=str(tmp_path),
+            content_type="article"
+        )
+
+        with patch("kb_pipeline.processors.base.get_settings") as mock_settings:
+            mock_settings.return_value = MagicMock()
+            with patch.object(
+                DownloadProcessor, '_get_adapter', return_value=mock_bilibili_article_adapter
+            ):
+                processor = DownloadProcessor(state_manager=mock_state_manager)
+                result = await processor.process(input_data)
+
+        assert result.success is True
+
+        # Check file paths follow naming convention
+        assert "bilibili_CV123_metadata.json" in result.metadata_file
+        assert "bilibili_CV123_content.md" in result.content_file
+
+        # Check files exist
+        assert Path(result.metadata_file).exists()
+        assert Path(result.content_file).exists()
+
+
+class TestDownloadProcessorModuleExport:
+    """Tests for DownloadProcessor module export."""
+
+    def test_download_processor_importable_from_processors(self):
+        """Test 4: DownloadProcessor can be imported from kb_pipeline.processors"""
+        from kb_pipeline.processors import DownloadProcessor
+
+        assert DownloadProcessor is not None
+        assert hasattr(DownloadProcessor, 'STEP_NAME')
+        assert DownloadProcessor.STEP_NAME == "download"
+
+    def test_all_processors_exported(self):
+        """All processors should be exported from kb_pipeline.processors"""
+        from kb_pipeline.processors import BaseProcessor, ParseProcessor, DownloadProcessor, ASRProcessor
+
+        assert BaseProcessor is not None
+        assert ParseProcessor is not None
+        assert DownloadProcessor is not None
+        assert ASRProcessor is not None