Fix : app unresponsive on startup (#4668)

openhands/server/session/session.py

@@ -139,7 +139,7 @@ class Session:
             await self.send(event_to_dict(event))
         # NOTE: ipython observations are not sent here currently
         elif event.source == EventSource.ENVIRONMENT and isinstance(
-            event, CmdOutputObservation
+            event, (CmdOutputObservation, AgentStateChangedObservation)
         ):
             # feedback from the environment to agent actions is understood as agent events by the UI
             event_dict = event_to_dict(event)