Classifies the current main-slot holder when a temp stream reaches its auto-promote window.
Call only after polling YouTube for the main holder's current lifecycle status.
Parameters
mainSlotStream: MainSlotSnapshot
Armed main-slot livestream, if any.
now: Date
Current time; used only to avoid releasing a main stream before its scheduled start.
Classifies the current main-slot holder when a temp stream reaches its auto-promote window. Call only after polling YouTube for the main holder's current lifecycle status.