Yes, you mentioned arco, but oceania was the one who just cast arcane nexus and gift of nature's bounty. But if you want to feel better about it, then go ahead and take credit for not saying I told you so.
Okay, seriously, I'd have let it go at that, but since you choose to use the phrase "I told you so"... is it that important that you "prove me wrong", however tenuously?
I made the observation about Arco being in a position that looked indomitable "barring a a prompt dogpile coupled with some serious late-game shenanigans". A turn or three later, Oceania cast a very nasty combination of globals. Like Arco, I didn't see it coming, so I made a reference to them engaging in precisely the sort of "serious late-game shenanigans" (I even used
the exact same phrase!) that could overcome Arco's rather-large edge. This wasn't meant as some deep prognostication; this was meant to say "I didn't see that coming (because everyone's been pretty passive and not showing much initiative, truth be told), and OMG ouch". No more, no less.
Having said that, per a quick test in Debug Mod you should be fine so long as you're only forging 1-gem items, even if you forge a bunch of them at once.
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Oceania, do you really have no plan but "turtle"? Between GoH, GoNB, and AN, if you have Alteration 9 I'd be expecting chain Armageddons to eliminate any possible blood economies and to shrink un-Gifted gold economies below a sustainable level (as well as whacking a whole lot of stockpiled un-other-Gifted troops - particularly markatas, obviously), so all that would remain would be the gem economies that feed your Nexus.