I'm trying to align all tab creation behavior with tab-bar-tab-post-open-functions. Even the first tab should be considered "opened" by the system and call people's functions on the hook. That tab, if you close it, does call the close hooks correctly and that's aligned, at least. If the open hook doesn't get called, then those tabs have to be treated in a special way and that creates bugs and burden. Not sure how relevant it is what I do in my custom hook that should get called for the implied opened first frames but doesn't.