fix(plugins): write BigQuery analytics rows when invocation agent is None

Workflow-driven invocations with deterministic nodes leave
InvocationContext.agent as None, so reading ReadonlyContext.agent_name raised
AttributeError and BigQueryAgentAnalyticsPlugin silently dropped the event row.
Resolve the agent column defensively (running agent name, else the source
Event.author, else null) so rows are written regardless of agent being None.

Co-authored-by: Haiyuan Cao <haiyuan@google.com>
PiperOrigin-RevId: 930097637

Author: haiyuan-eng-google

src/google/adk/plugins/bigquery_agent_analytics_plugin.py

@@ -2937,6 +2937,33 @@ def _extract_latency(
       latency_json["time_to_first_token_ms"] = event_data.time_to_first_token_ms
     return latency_json or None
 
+  @staticmethod
+  def _resolve_agent_label(
+      callback_context: CallbackContext,
+      source_event: Optional["Event"],
+  ) -> Optional[str]:
+    """Resolves the ``agent`` column without raising when no agent is set.
+
+    ``CallbackContext.agent_name`` dereferences
+    ``InvocationContext.agent.name`` with no None guard, but ``agent`` is
+    legitimately ``None`` for workflow-driven invocations with deterministic
+    nodes. Reading it at row-build time then raised ``AttributeError``, which
+    ``@_safe_callback`` swallowed, silently dropping the row (issue #6063).
+
+    Resolution order:
+
+    * running agent present → ``agent.name``;
+    * no agent but a source Event → ``Event.author`` (the emitting node), a
+      more meaningful workflow label than a sentinel;
+    * callback-only row with neither → ``None`` (SQL NULL).
+    """
+    agent = getattr(callback_context._invocation_context, "agent", None)
+    if agent is not None:
+      return getattr(agent, "name", None)
+    if source_event is not None:
+      return getattr(source_event, "author", None)
+    return None
+
   def _build_adk_envelope(
       self,
       callback_context: CallbackContext,
@@ -3189,7 +3216,9 @@ async def _log_event(
     row = {
         "timestamp": timestamp,
         "event_type": event_type,
-        "agent": callback_context.agent_name,
+        "agent": self._resolve_agent_label(
+            callback_context, event_data.source_event
+        ),
         "user_id": callback_context.user_id,
         "session_id": callback_context.session.id,
         "invocation_id": callback_context.invocation_id,

tests/unittests/plugins/test_bigquery_agent_analytics_plugin.py

@@ -1802,6 +1802,91 @@ async def test_log_event_with_custom_tags(
     attributes = json.loads(log_entry["attributes"])
     assert attributes["custom_tags"] == custom_tags
 
+  def test_resolve_agent_label_prefers_running_agent(self, callback_context):
+    """agent present → agent.name, regardless of any source event."""
+    event = event_lib.Event(author="WorkflowNodeA")
+    label = bigquery_agent_analytics_plugin.BigQueryAgentAnalyticsPlugin._resolve_agent_label(
+        callback_context, event
+    )
+    assert label == "MyTestAgent"
+
+  def test_resolve_agent_label_falls_back_to_event_author(
+      self, callback_context
+  ):
+    """No agent + source Event → Event.author (the emitting node)."""
+    callback_context._invocation_context.agent = None
+    event = event_lib.Event(author="WorkflowNodeA")
+    label = bigquery_agent_analytics_plugin.BigQueryAgentAnalyticsPlugin._resolve_agent_label(
+        callback_context, event
+    )
+    assert label == "WorkflowNodeA"
+
+  def test_resolve_agent_label_null_for_callback_only_row(
+      self, callback_context
+  ):
+    """No agent and no source Event → None (SQL NULL)."""
+    callback_context._invocation_context.agent = None
+    label = bigquery_agent_analytics_plugin.BigQueryAgentAnalyticsPlugin._resolve_agent_label(
+        callback_context, None
+    )
+    assert label is None
+
+  @pytest.mark.asyncio
+  async def test_log_event_survives_none_agent_with_event_author(
+      self,
+      bq_plugin_inst,
+      mock_write_client,
+      callback_context,
+      dummy_arrow_schema,
+  ):
+    """Regression for #6063: None agent falls back to source event author."""
+    # Workflow-driven invocations leave ``InvocationContext.agent`` as None.
+    # Reading ``callback_context.agent_name`` then raised ``AttributeError``,
+    # which ``@_safe_callback`` swallowed, silently dropping the BigQuery row.
+    # The row must now be written with the source Event's author as the label.
+    callback_context._invocation_context.agent = None
+    event = event_lib.Event(author="WorkflowNodeA")
+
+    await bq_plugin_inst._log_event(
+        "TEST_EVENT",
+        callback_context,
+        raw_content="test content",
+        event_data=bigquery_agent_analytics_plugin.EventData(
+            source_event=event
+        ),
+    )
+    await asyncio.sleep(0.01)
+    log_entry = await _get_captured_event_dict_async(
+        mock_write_client, dummy_arrow_schema
+    )
+
+    assert log_entry["event_type"] == "TEST_EVENT"
+    assert log_entry["agent"] == "WorkflowNodeA"
+
+  @pytest.mark.asyncio
+  async def test_log_event_survives_none_agent_without_source_event(
+      self,
+      bq_plugin_inst,
+      mock_write_client,
+      callback_context,
+      dummy_arrow_schema,
+  ):
+    """Regression for #6063: callback-only row with no agent writes null."""
+    callback_context._invocation_context.agent = None
+
+    await bq_plugin_inst._log_event(
+        "TEST_EVENT",
+        callback_context,
+        raw_content="test content",
+    )
+    await asyncio.sleep(0.01)
+    log_entry = await _get_captured_event_dict_async(
+        mock_write_client, dummy_arrow_schema
+    )
+
+    assert log_entry["event_type"] == "TEST_EVENT"
+    assert log_entry["agent"] is None
+
   @pytest.mark.asyncio
   async def test_on_model_error_callback_logs_correctly(
       self,