Connections in background tabs may disconnect if throttled by Chrome/Safari

Chrome, the various Chromium variants, and Safari will heavily throttle JavaScript timers within background tabs and windows. This prevents the tunnel from issuing its keep-alive ping and may result in a disconnect. See:

• https://developer.chrome.com/blog/timer-throttling-in-chrome-88/
• https://github.com/SignalR/SignalR/issues/4536

It's possible that there is a way to work around this and continue sending keep-alives in the background, such as by simply changing the originating event of those timers:

https://bugs.chromium.org/p/chromium/issues/detail?id=1186569#c3