How do you best build a society so it is resistant to Chaos (or any other similar existential near-omnipresent...

These are plainly obvious answers, assume you actually want your populace to stay vaguely human.

put the soul in an iron cage.

>fanatic ideologues
>implying that is not very human

Well maybe they Study the corrupting force and actually understand how it works and they do a concious fully informed decision to not become chaosfags

Make the society run by sky net. Have the computer overlord put computers in their heads that monitor ungood think. Don't tell anyone how the implants actually work. If the system detects corruption, the person has to be re-educated or killed. There now you keep your society some what human while having the perks of a souless computer running it.

Can't computers be corrupted by chaos in 40k?

Develop a belief system that subtly mocks the extremes of Chaos at every turn. Make up tales and fables of people surrendering to their desires and destroying themselves as Aesops for children.

Dress up Chaos as something to be laughed at, derided, and ignored.

...Kinda? A simple computer like the one you're using isn't going to sprout tentacles without SERIOUS warp-fuckery but an AI pretty much falls to Chaos by default.

Educate the entire population into the dangers of Chaos. Make them know that giving up to emotion feed Chaos.

Some think that the Iron Men happened when mankind started experimenting with Warp-Based AI, like Machine Spirits.

I don't remember if the virus in Dan Abnett's "Know no Fear" was chaos based or not, but either way it seems chaos isn't afraid of digital warfare.

Eldars had AI for millions of years and there was never an AI rebellion.

Mind, eldar tech is as much psychic power as it is material crafting. Probably less of an AI and more of a synthetic soul.

Well, it also took tens of thousands of years for the Iron Men to happen.

Who cares, Run skynet on the cloud have millions of redundant systems scanning the network and themselves. Anytime irregularities are detected that server is immediately formatted and replaced.

Turn them into lizardmen?

This basically. The antidote to Chaos is Order, and religion is the most compelling kind of Order.

Religion.

In Mechanicum, the Traitor forges hack the planet with scrap code generators. It says that the things producted under infected systems looked abhorrent, like chaos warped. There is also the Obliterator virus who could probably fuse Anons to their computers and fleshlights.
Does it mean an AI can just fall by itself to Chaos as a result of long meditations? Who knows. Can PCs get infected by Chaos taint through foreign agents? Totally.

...

Chaos Androids were a thing, so yes.

What about a sort of ideology/pseudo-religion which promotes the supremacy of humanity, their right to survive, and promotes the beliefs of previous generations and the emulation of various mythological heroes. Even though they know it's false, the heroes were archetypes, anyway, and it wouldn't hold that there is a supreme being or something above humanity to be worshipped in any way. It would be designed as a tool of social order and cohesion. Something you can indoctrinate children with early on. Combine this with making knowledge of chaos public, stressing that it is the ultimate enemy of humanity and showing what happens to anyone who tries to do anything other than exterminate it at every turn. Media, celebrities and everything else would be controlled as much as possible to further support this idea of extreme hatred for Chaos and always bettering oneself.

This would be helped by having everyone living in 100% monitored self-sufficient fortress arcologies. People would live relatively good lives, with technology providing them with basic income and a large variety high quality entertainment being cheap to get. Schools would be mandatory and basically be government run indoctrination camps. The economy would be carefully controlled by high level dumb AIs and specialised transhumans to make sure that it runs smoothly, the military would be idolised and even lowly grunts would be treated as valuable and (if they survive) be very well payed. The society would be highly meritocratic.

Basically just turn your entire civilisation into one giant anti-chaos pro-human perpetual propaganda machine which is actually well designed and works unlike the Imperium.

By ensuring everyone is satisfied with their lives. Chaos cults typically arise from those plotting to overthrow the current order or seeking new pleasures. However Chaos is nothing if not adaptable and humans are terribly fickle, so even then Chaos would likely find a way.

Follow the path of Craftworld Eldar or Dark Eldar. None of them seem to ever fall into Chaos.

>here is also the Obliterator virus who could probably fuse Anons to their computers and fleshlights.

You do realize that there are subcultures that would absolutely sign up if you told them that they were going to get their dicks rubbed whenever they shitpost for all of eternity?

Turn everyone into soulless computers, duh.