events: Do nothing in apply_event for restart events.

These signal that the Tornado process restarted, which in itself is
not notable for apply_events.

zerver/lib/events.py

@@ -1531,6 +1531,9 @@ def apply_event(
         # possible, but the worst expected outcome is that the client
         # retains the old JS instead of reloading.
         logging.warning("Got a web_reload_client event during apply_events")
+    elif event["type"] == "restart":
+        # The Tornado process restarted.  This has no effect; we ignore it.
+        pass
     else:
         raise AssertionError("Unexpected event type {}".format(event["type"]))
 

zerver/tests/test_events.py

@@ -248,6 +248,7 @@ from zerver.tornado.event_queue import (
     clear_client_event_queues_for_testing,
     create_heartbeat_event,
     mark_clients_to_reload,
+    send_restart_events,
     send_web_reload_client_events,
 )
 from zerver.views.realm_playgrounds import access_playground_by_id
@@ -3478,6 +3479,13 @@ class NormalActionsTest(BaseAction):
         events = self.verify_action(lambda: do_set_zoom_token(self.user_profile, None))
         check_has_zoom_token("events[0]", events[0], value=False)
 
+    def test_restart_event(self) -> None:
+        self.verify_action(
+            lambda: send_restart_events(),
+            num_events=1,
+            state_change_expected=False,
+        )
+
     def test_web_reload_client_event(self) -> None:
         self.verify_action(
             lambda: send_web_reload_client_events(),