Update src/a2a/utils/artifact.py

Co-authored-by: gemini-code-assist[bot] <176961590+gemini-code-assist[bot]@users.noreply.github.com>

Author: kevinlu310

src/a2a/utils/artifact.py

@@ -123,10 +123,10 @@ def __init__(
         name: str = 'response',
         artifact_id: str | None = None,
     ) -> None:
-        self.context_id = context_id
-        self.task_id = task_id
-        self.name = name
-        self.artifact_id = artifact_id or str(uuid.uuid4())
+        self._context_id = context_id
+        self._task_id = task_id
+        self._name = name
+        self._artifact_id = artifact_id or str(uuid.uuid4())
 
     def append(self, text: str) -> TaskArtifactUpdateEvent:
         """Emit a chunk to be appended to the streaming artifact.