Task 3.3: Update ProgressService to use key as identifier

- Added optional 'key' and 'folder' fields to ProgressUpdate dataclass
- key: Primary series identifier (provider key, e.g., 'attack-on-titan')
- folder: Optional series folder name for display (e.g., 'Attack on Titan (2013)')
- Updated start_progress() and update_progress() methods to accept key/folder parameters
- Enhanced to_dict() serialization to include key/folder when present
- Updated all docstrings to clarify identifier usage
- Added 5 new comprehensive unit tests for key/folder functionality
- All 25 ProgressService tests passing
- Updated infrastructure.md with series identifier documentation
- Maintains backward compatibility - fields are optional
- Completed Phase 3, Task 3.3 of identifier standardization initiative

tests/unit/test_progress_service.py

@@ -508,3 +508,94 @@ class TestProgressService:
         assert progress.metadata["initial"] == "value"
         assert progress.metadata["additional"] == "data"
         assert progress.metadata["speed"] == 1.5
+
+    @pytest.mark.asyncio
+    async def test_progress_with_key_and_folder(self, service):
+        """Test progress tracking with series key and folder."""
+        # Start progress with key and folder
+        update = await service.start_progress(
+            progress_id="download-series-1",
+            progress_type=ProgressType.DOWNLOAD,
+            title="Downloading Attack on Titan",
+            key="attack-on-titan",
+            folder="Attack on Titan (2013)",
+            total=100,
+        )
+
+        assert update.key == "attack-on-titan"
+        assert update.folder == "Attack on Titan (2013)"
+
+        # Verify to_dict includes key and folder
+        dict_repr = update.to_dict()
+        assert dict_repr["key"] == "attack-on-titan"
+        assert dict_repr["folder"] == "Attack on Titan (2013)"
+
+        # Update progress and verify key/folder are preserved
+        updated = await service.update_progress(
+            progress_id="download-series-1",
+            current=50,
+        )
+
+        assert updated.key == "attack-on-titan"
+        assert updated.folder == "Attack on Titan (2013)"
+
+    @pytest.mark.asyncio
+    async def test_progress_update_key_and_folder(self, service):
+        """Test updating key and folder in existing progress."""
+        # Start without key/folder
+        await service.start_progress(
+            progress_id="test-1",
+            progress_type=ProgressType.SCAN,
+            title="Test Scan",
+        )
+
+        # Update with key and folder
+        updated = await service.update_progress(
+            progress_id="test-1",
+            key="one-piece",
+            folder="One Piece (1999)",
+            current=10,
+        )
+
+        assert updated.key == "one-piece"
+        assert updated.folder == "One Piece (1999)"
+
+        # Verify to_dict includes the fields
+        dict_repr = updated.to_dict()
+        assert dict_repr["key"] == "one-piece"
+        assert dict_repr["folder"] == "One Piece (1999)"
+
+    def test_progress_update_to_dict_without_key_folder(self):
+        """Test to_dict doesn't include key/folder if not set."""
+        update = ProgressUpdate(
+            id="test-1",
+            type=ProgressType.SYSTEM,
+            status=ProgressStatus.STARTED,
+            title="System Task",
+        )
+
+        result = update.to_dict()
+
+        # key and folder should not be in dict if not set
+        assert "key" not in result
+        assert "folder" not in result
+
+    def test_progress_update_creation_with_key_folder(self):
+        """Test creating progress update with key and folder."""
+        update = ProgressUpdate(
+            id="test-1",
+            type=ProgressType.DOWNLOAD,
+            status=ProgressStatus.STARTED,
+            title="Test Download",
+            key="naruto",
+            folder="Naruto (2002)",
+            total=100,
+        )
+
+        assert update.key == "naruto"
+        assert update.folder == "Naruto (2002)"
+
+        # Verify to_dict includes them
+        result = update.to_dict()
+        assert result["key"] == "naruto"
+        assert result["folder"] == "Naruto (2002)"