How is it guaranteed that zle is active during sched call?

[Sebastian Gniazdowski <sgniazdowski@xxxxxxxxx>]

Hello,
I saw codes on the internet that advise doing "zle && zle
reset-prompt" when wanting a Zle change from a sched call, e.g. here (on
the bottom, last 11 item):

http://chneukirchen.org/blog/archive/2013/03/10-fresh-zsh-tricks-you-may-not-know.html

I once too occurred sched calls that indeed were zle == false, and
added such "zle &&" guard too. Now when I test I always get zle
active. When to expect lack of zle, can this be predicted? Will
re-scheduling (with +1 second) help?

Best regards,
Sebastian Gniazdowski