fix(agents): record artifact_delta from before/after agent callbacks

src/google/adk/agents/base_agent.py

@@ -567,7 +567,8 @@ async def _handle_agent_callbacks(
       end_invocation_on_content: Whether returned content ends the invocation.
 
     Returns:
-      Optional[Event]: an event if a callback provides content or changed state.
+      Optional[Event]: an event if a callback provides content or changed state
+        or artifacts.
     """
     callback_context = CallbackContext(ctx)
 
@@ -599,7 +600,10 @@ async def _handle_agent_callbacks(
         ctx.end_invocation = True
       return ret_event
 
-    if callback_context.state.has_delta():
+    if (
+        callback_context.state.has_delta()
+        or callback_context._event_actions.artifact_delta
+    ):
       return Event(
           invocation_id=ctx.invocation_id,
           author=self.name,

tests/unittests/agents/test_base_agent.py

@@ -32,6 +32,7 @@
 from google.adk.agents.invocation_context import InvocationContext
 from google.adk.agents.llm_agent import LlmAgent
 from google.adk.apps.app import ResumabilityConfig
+from google.adk.artifacts.in_memory_artifact_service import InMemoryArtifactService
 from google.adk.events.event import Event
 from google.adk.plugins.base_plugin import BasePlugin
 from google.adk.plugins.plugin_manager import PluginManager
@@ -720,6 +721,73 @@ async def test_run_async_with_async_after_agent_callback_append_reply(
   )
 
 
+async def _before_agent_callback_save_artifact(
+    callback_context: CallbackContext,
+) -> None:
+  await callback_context.save_artifact(
+      'before_agent.txt', types.Part.from_text(text='saved before agent')
+  )
+
+
+async def _after_agent_callback_save_artifact(
+    callback_context: CallbackContext,
+) -> None:
+  await callback_context.save_artifact(
+      'after_agent.txt', types.Part.from_text(text='saved after agent')
+  )
+
+
+@pytest.mark.asyncio
+async def test_run_async_before_agent_callback_records_artifact_delta(
+    request: pytest.FixtureRequest,
+):
+  # Arrange
+  agent = _TestingAgent(
+      name=f'{request.function.__name__}_test_agent',
+      before_agent_callback=_before_agent_callback_save_artifact,
+  )
+  parent_ctx = await _create_parent_invocation_context(
+      request.function.__name__, agent
+  )
+  parent_ctx.artifact_service = InMemoryArtifactService()
+
+  # Act
+  events = [e async for e in agent.run_async(parent_ctx)]
+
+  # Assert
+  # The first event records the artifact saved by before_agent_callback, the
+  # second event is the regular agent response.
+  assert len(events) == 2
+  assert events[0].author == agent.name
+  assert events[0].actions.artifact_delta == {'before_agent.txt': 0}
+  assert events[1].content.parts[0].text == 'Hello, world!'
+
+
+@pytest.mark.asyncio
+async def test_run_async_after_agent_callback_records_artifact_delta(
+    request: pytest.FixtureRequest,
+):
+  # Arrange
+  agent = _TestingAgent(
+      name=f'{request.function.__name__}_test_agent',
+      after_agent_callback=_after_agent_callback_save_artifact,
+  )
+  parent_ctx = await _create_parent_invocation_context(
+      request.function.__name__, agent
+  )
+  parent_ctx.artifact_service = InMemoryArtifactService()
+
+  # Act
+  events = [e async for e in agent.run_async(parent_ctx)]
+
+  # Assert
+  # The first event is the regular agent response, the second event records
+  # the artifact saved by after_agent_callback.
+  assert len(events) == 2
+  assert events[1].author == agent.name
+  assert events[1].actions.artifact_delta == {'after_agent.txt': 0}
+
+
 @pytest.mark.asyncio
 @pytest.mark.parametrize('method_name', ['run_async', 'run_live'])
 @pytest.mark.parametrize('exit_type', ['cancelled', 'generator_exit'])