Fix race condition in python <= 3.12

Author: pstephengoogle

src/a2a/server/events/event_consumer.py

@@ -101,7 +101,6 @@ async def consume_all(self) -> AsyncGenerator[Event]:
                 logger.debug(
                     f'Dequeued event of type: {type(event)} in consume_all.'
                 )
-                yield event
                 self.queue.task_done()
                 logger.debug(
                     'Marked task as done in event queue in consume_all'
@@ -123,10 +122,16 @@ async def consume_all(self) -> AsyncGenerator[Event]:
                     )
                 )
 
+                # Make sure the yield is after the close events, otherwise
+                # the caller may end up in a blocked state where this
+                # generator isn't called again to close things out and the
+                # other part is waiting for an event or a closed queue.
                 if is_final_event:
                     logger.debug('Stopping event consumption in consume_all.')
                     await self.queue.close()
+                    yield event
                     break
+                yield event
             except TimeoutError:
                 # continue polling until there is a final event
                 continue