There's something going on with the image cache on Cirrus where the images
are sometimes vanishing from the cache, thus causing builds to fail
because it can't load them. This forces a rebuild of all of the images,
thus refreshing the cached version of all of them.
This exposes Broker's new WebSocket support in Zeek. To enable it,
call `Broker::listen_websocket()`. Zeek will then start listening on
port 9997 for incoming WebSocket connections.
See the Broker documentation for a description of the message format
expected over these WebSocket connections.
