* test_connection_banner: Improve assertions
* Actually assert on the presence or absense of the connection banner
* Update XPATH selector to find the connection toast
* Add event handling while backend down to verify queue functionality
* Bring backend down while an event is running to ensure queue does not get
blocked (#3404)
* state.js: set event_processing = false when websocket connects
In case an event was pending when the websocket went down, allow further events
to be processed when it comes back up.
Fix#3404
* test_connection_banner: wait for token indicating backend is connected
* test_connection_banner: increase delay time
make the time window longer in which the backend can go down and get stuck in
event_processing=true for better test reliability
* Ensure the redis connection is reset in new backend thread
Redis has an event loop affinity and needs to be attached to the event loop
that the thread is running.
* Reset event_processing on disconnect
* if the socket never comes back up, it still allows client-side events to be
processed
* on_mount events may start running before the socket is up, so resetting the
flag on connect may break event determinism (test_event_chain.py)
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