Change:
return; } <del> updateCommentThread(commentThread: languages.CommentThread<T>) { </del> <ins> updateCommentThread(commentThread: languages.CommentThread<T>, preserveFocus: boolean) { </ins> const oldCommentsLen = this._commentElements.length; const newCommentsLen = commentThread.comments ? commentThread.comments.length : 0;

Discussion:
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To clarify our use case a bit more: we don't expect background updates to happening frequently (i.e. not live collaboration similar to Google Docs) but we might occasionally still receive a single new round of comments from a reviewer while the change author is currently typing a reply. As far as I know there is no way for our extension to learn if the Reply input is open with pending content, meaning we cannot delay automatic background updates to wait until we won't interrupt the user.
Focus goes back to so it appears to be lost, not stolen.
It's a surprising and inconvenient behavior that updating fields in vscode.CommentThread steals focus.

It'd be great if the APIs are updated not to steal the focus. Our extension (for Gerrit code review integration) has a method to decorate a vscode.CommentThread, which currently always updates all the CommenThread's fields even if there's a field having no change. This construct makes the implementation simple, removing the need of checking the equality for every field. All was good - until we realized the bug of the focus being stolen at an unexpected timing while the user is editing the code. We will workaround the issue by introducing equality check everywhere, but I hope we could remove the workaround in future.