there is no "WebHandler for a session".
There is a webHandler for each incoming request. So over time, a session will have zillions of web handlers.
And when the user is "doing nothing" (ie pretty much all the time) there is no webHandler at all for the session.
>> I want to do this not in response to user interaction but from a separate process in the webserver application,
The web is built on a request/response system. The browser makes a connection, posts a request, gets a response, and closes the connection. So you can't "push" stuff at the browser because there's no connection to push it down. To have a connnection to the browser "open and listening for push stuff" we get into the subject of WebScokets.https://www.capesoft.com/docs/NetTalk12/NetTalkWebBasic.htm#WebSockets
Basically a web socket is a "back door" connection between the browser and server which you can use to push data to the server, but only if the browser is on a page with a WebSocket connection.