The point I'm making is not about Omega's trustworthiness, but about my beliefs.

If Omega is trustworthy AND I'm confident that Omega is trustworthy, then I will one-box. The reason I will one-box is that it follows from what Omega has said that one-boxing is the right thing to do, and I believe that Omega is trustworthy. It feels completely bizarre to one-box, but that's because it's completely bizarre for me to believe that Omega is trustworthy; if I have already assumed the latter, then one-boxing follows naturally. It follows just as naturally with a transparent box, or with a box full of pit vipers, or with a revolver which I'm assured that, fired at my head, will net me a million dollars. If I'm confident that Omega's claims are true, I one-box (or fire the revolver, or whatever).

If Omega is not trustworthy AND I'm confident that Omega is trustworthy, then I will still one-box. It's just that in that far-more-ordinary scenario, doing so is a mistake.

I cannot imagine a mechanism whereby I become confident that Omega is trustworthy, but if the setup of the thought experiment presumes that I am confident, then what follows is that I one-box.

No precommitment is required. All I have to "precommit" to is to acting on the basis of what I believe to be true at the time. If that includes crazy-seeming beliefs about Omega, then the result will be crazy-seeming decisions. If those crazy-seeming beliefs are true, then the result will be crazy-seeming correct decisions.