fix(a2a): send append=True for the final chunk of a streamed artifact

src/google/adk/a2a/converters/from_adk_event.py

@@ -184,7 +184,10 @@ def convert_event_to_a2a_events(
 
       artifact_id = agents_artifacts.get(agent_name)
       if artifact_id:
-        append = partial
+        # A prior chunk already created this artifact (append=False), so
+        # every subsequent chunk -- including the final, non-partial one --
+        # must append rather than replace it.
+        append = True
         if not partial:
           del agents_artifacts[agent_name]
       else:

tests/unittests/a2a/converters/test_from_adk.py

@@ -76,6 +76,44 @@ def test_convert_event_to_a2a_events_artifact_update(self):
     assert result[0].artifact.parts == [mock_a2a_part]
     assert "agent-1" in agents_artifacts  # Artifact ID should be stored
 
+  def test_convert_event_to_a2a_events_final_chunk_appends(self):
+    """The final (non-partial) chunk of a stream must still append, not
+
+    replace, the artifact created by the first chunk.
+    """
+    self.mock_event.content = genai_types.Content(
+        parts=[genai_types.Part(text="hello")], role="model"
+    )
+    self.mock_event.author = "agent-1"
+    self.mock_event.partial = True
+
+    agents_artifacts = {}
+    mock_convert_part = Mock(return_value=[_compat.make_text_part("hello")])
+
+    first = convert_event_to_a2a_events(
+        self.mock_event,
+        agents_artifacts,
+        task_id="task-123",
+        context_id="context-456",
+        part_converter=mock_convert_part,
+    )
+    assert first[0].append is False
+    artifact_id = first[0].artifact.artifact_id
+    assert agents_artifacts["agent-1"] == artifact_id
+
+    self.mock_event.partial = False
+    final = convert_event_to_a2a_events(
+        self.mock_event,
+        agents_artifacts,
+        task_id="task-123",
+        context_id="context-456",
+        part_converter=mock_convert_part,
+    )
+
+    assert final[0].append is True
+    assert final[0].artifact.artifact_id == artifact_id
+    assert "agent-1" not in agents_artifacts
+
   def test_convert_event_to_a2a_events_error(self):
     """Test conversion of event with error to TaskStatusUpdateEvent."""
     self.mock_event.error_code = "ERR001"