Its done through a Javascript loading system.
I have no idea how it works.
You should really try to get this working through events, capabilities, and other non-ASM methods first, though. The main problem you have is not ItemStacks not being ticked, but containers not applying update ticks to their inventory and there's no way to enforce that compliance.
But if you want to coremod, feel free to figure out how to do so yourself. Its supported only in the sense that a system is available for those that know how to use it because core modding is a last resort.