• Foundries require Turbo Splitters
• Turbo Splitters require Electrolyte
• Electrolyte requires Molten Copper
• Molten Copper can only be made in a foundry.

I think maybe this isn't getting caught because Molten copper isn't part of the "ingredients" that lead to the foundry, but rather part of the "made in" requirements.

This is on seed 0, so I'm surprised it hasn't been caught before. Maybe I'm missing something? Is there any other way to get Molten copper or a foundry? Or maybe my specific settings for Algorithm/Delinearization lead me to a setup that hasn't been explored before and I need to cheat myself a foundry to escape?

What exact settings/mods are you using? The world changes completely even with small tweaks in those things, so I would need to know in order to debug. You can share a screenshot of the settings, or a zip file with an empty save that I can sync to.

Sure thing, here's a screenshot:
https://images.steamusercontent.com/ugc/14377168777684149713/8E76FF67F3E3BB49E2AFAA284EB0499FA6CE22A0/?imw=5000&imh=5000&ima=fit&impolicy=Letterbox&imcolor=%23000000&letterbox=false

The bug has been reproduced, but I'm not sure what causes it. Logic already accounts for everything, including where things are made, so it must be a more subtle issue. You can cheat in a foundry right now or I can tell you what to put into the overrides box to make things reachable if you want to keep modded achievements for some reason.

Just to be sure I ran the reachability algorithm on your seed and it reported that foundries were indeed a softlock for the reasons you stated. This also confirms that there is an issue in one of the algorithms (probably an interaction between the new unified ones and the old ones since that's the newest part of the randomizer).

If it helps with peace of mind, upon forcing foundries in, the reachability algorithm found no issue getting to promethium science (I didn't check every single item but hopefully that means no impossibilities elsewhere either).

I appreciate the diligence! I'll add myself a foundry to escape the softlock since you've confirmed its not just me missing something. Hope this helps uncover whatever the problem is. This is a super cool mod- thanks for making it!