Option to control virtual background programmatically

We are building an interview platform on the Calls SDK v5. We already have in-call Virtual Background working via the session statics (setVirtualBackgroundBlurLevel, setVirtualBackgroundImage, clearVirtualBackground, showVirtualBackgroundDialog) with hideVirtualBackgroundButton: false. That works well inside an active session.

We now need VB (blur + preset image) available on our custom pre-join / waiting-room screen, before joinSession is called, with a live preview in the camera tile. Your own hosted demo at calls.cometchat.io also has no VB on its pre-join lobby (screenshot attached), so we want to confirm whether this is possible at all.

Questions:

1. Pre-join VB preview — Is there any supported public API to apply/preview Virtual Background on a local MediaStreamTrack obtained from our own getUserMedia, before an active session exists? The VB engine appears to be bound to the local track only inside an active joinSession. We see previewTrack / previewVirtualBackground slices in the store but found no public setter. Is a green-room / pre-join VB API planned or available?

2. Carry selection into the call — If pre-join VB is not supported, is there a supported way to pass a pre-selected background (blur level or image) into joinSession so it applies immediately on join without the user re-opening the in-call dialog? Note CallSettingsBuilder.setVirtualBackground() is marked @deprecated / has no effect.

3. Dialog-highlight sync — Calling setVirtualBackgroundBlurLevel(n) applies the live blur but does not update the backgrounds[].selected / selectedBackgroundId state that drives the dialog highlight. Result: blur is active but the dialog shows "None", and pressing Done then clears the blur. The sync action (selectBackground(id)) is not exported. Is there a public API to programmatically select a background so the dialog highlight stays in sync?