I don't know how this plays out specifically in psychosis, but ascribing intentionality in general, and specifically ascribing adversariality, seems like an especially important dimension / phenomenon. (Cf. https://en.wikipedia.org/wiki/Ideas_and_delusions_of_reference )

Ascribing adversariality in particular might be especially prone to setting off a self-sustaining reaction.

Consider first that when you ascribe adversariality, things can get weird fast. Examples:

• If Bob thinks Alice is secretly hostile towards Bob, trust breaks down. Propositional statements from Alice are interpreted as false, lies, or subtler manipulations with hidden intended effects.
• This generally winds Bob up. Every little thing Alice says or does, if you take as given the (probably irrational) assumption of adversariality, would rationally give Bob good reason to spin up a bunch of computation looking for possible plans Alice is doing. This is first of all just really taxing for Bob, and distracting from more normal considerations. And second of all it's a local bias, pointing Bob to think about negative outcomes; normally that's fine, all attention-direction is a local bias, but since the situation (e.g. talking to Alice) is ongoing, Bob may not have time and resources to compute everything out so that he also thinks of, well maybe Alice's behavior is just normal, or how can I test this sanely, or alternative hypotheses other than hostility from Alice, etc.
• This cuts off flow of information from Alice to Bob.
• This cuts off positive sum interactions between Alice and Bob; Bob second guesses every proposed truce, viewing it as a potential false peace.
• Bob might start reversing the pushes that Alice is making, which could be rational on the supposition that Alice is being adversarial. But if Alice's push wasn't adversarial and you reverse it, then it might be self-harming. E.g. "She's only telling me to try to get some sleep because she knows I'm on the verge of figuring out XYZ, I better definitely not sleep right now and keep working towards XYZ".
• Are they all good or all out to get me? If Bob thinks Alice is adversarial, and Alice is not adversarial, and Carmi and Danit are also not adversarial, then they look like Alice and so Bob might think they are adversarial.
• And suppose, just suppose, that one person does do something kinda adversarial. Like suggest that maybe you really need to take some sort of stronger calming drug, or even see a doctor. Well, maybe that's just one little adversariality--or maybe this is a crack in the veneer, the conspiracy showing through. Maybe everyone has been trying really hard to merely appear non-adversarial; in that case, the single crack is actually a huge piece of evidence. (Cf. https://sideways-view.com/2016/11/14/integrity-for-consequentialists/ ; https://en.wikipedia.org/wiki/Splitting_(psychology))
• The derivative, or the local forces, become exaggerated in importance. If Bob perceives a small adversarial push from Alice, he feels under attack in general. He computes out: There is this push, and there will be the next and the next and the next; in aggregate this leads somewhere I really don't want; so I must push back hard, now. So Bob is acting crazy, seemingly having large or grandiose responses to small things. (Cf. https://en.wikipedia.org/wiki/Splitting_(psychology) )
• Methods of recourse are broken; Bob has no expectation of being able to JOOTS and be caught by the social fabric / by justice / by conversation and cooperative reflection. (I don't remember where, maybe in some text about double binds, but there was something about: Someone is in psychosis, and when interviewed, they immediately give strange, nonsensical, or indirect answers to an interviewer; but not because they couldn't give coherent answers--rather, because they were extremely distrustful of the interviewer and didn't want to tip off the interviewer that they might be looking to divulge some terrible secret. Or something in that genre, I'm not remembering it.)

Now, consider second that as things are getting weird, there's more grist for the mill. There's more weird stuff happening, e.g. Bob is pushing people around him into contexts that they lack experience in, so they become flustered, angry, avoidant, blissfully unattuned, etc. With this weird stuff happening, there's more for Bob to read into as being adversarial.

Third, consider that the ascription of adversariality doesn't have to be Cartesian. "Aliens / demons / etc. are transmitting / forcing thoughts into my head". Bob starts questioning / doubting stuff inside him as being adversarial, starts fighting with himself or cutting off parts of his mind.