fix: Emit $ai_trace events for agent spans instead of skipping

Agent spans now create $ai_trace events so that child spans (tools, etc.)
have a valid parent reference. Previously agent spans were skipped, which
caused orphaned $ai_parent_id references in tool spans.

Author: andrewm4894

posthog/ai/otel/exporter.py

@@ -231,10 +231,17 @@ def _span_to_event(self, span: ReadableSpan) -> Optional[Dict[str, Any]]:
                 error_message,
             )
 
-        # Agent run span → skip (PostHog UI auto-creates trace wrapper from generation events)
-        # The $ai_trace_id on generation events is sufficient for grouping
+        # Agent run span → $ai_trace
         if self._is_agent_span(span_name, attrs):
-            return None  # Don't emit separate $ai_trace events
+            return self._create_trace_event(
+                span,
+                attrs,
+                trace_id,
+                span_id,
+                latency,
+                is_error,
+                error_message,
+            )
 
         # Tool execution span → $ai_span
         if self._is_tool_span(span_name, attrs):

posthog/test/ai/otel/test_exporter.py

@@ -234,9 +234,9 @@ def test_generation_event_with_model_parameters(self, mock_client):
 
 
 class TestAgentSpanHandling:
-    """Tests for agent span handling (should be skipped)."""
+    """Tests for agent span handling ($ai_trace events)."""
 
-    def test_agent_span_is_skipped(self, mock_client):
+    def test_agent_span_creates_trace_event(self, mock_client):
         exporter = PostHogSpanExporter(mock_client, distinct_id="user_123")
 
         span = create_mock_span(
@@ -245,16 +245,21 @@ def test_agent_span_is_skipped(self, mock_client):
 
         exporter.export([span])
 
-        mock_client.capture.assert_not_called()
+        mock_client.capture.assert_called_once()
+        call_kwargs = mock_client.capture.call_args[1]
+        assert call_kwargs["event"] == "$ai_trace"
+        assert call_kwargs["properties"]["$ai_span_name"] == "TestAgent"
 
-    def test_invoke_agent_span_is_skipped(self, mock_client):
+    def test_invoke_agent_span_creates_trace_event(self, mock_client):
         exporter = PostHogSpanExporter(mock_client, distinct_id="user_123")
 
         span = create_mock_span(name="invoke_agent", attributes={})
 
         exporter.export([span])
 
-        mock_client.capture.assert_not_called()
+        mock_client.capture.assert_called_once()
+        call_kwargs = mock_client.capture.call_args[1]
+        assert call_kwargs["event"] == "$ai_trace"
 
 
 class TestToolSpanEventCreation: