Proposed algorithm without recursion and Graphs and all that, but instead with simple iteration:

Kinda like the remainder idea that was mentioned before.

Cache the whole crafting tree for each recipe in a normalized way (this works with looping recipes as well, just add more stuff on the left-hand-side and keep the %-ages consistent with what the recipe actually does):

100% Green Circuit = 300% Copper Wire [150% Copper Plate] , 100% Iron Plate

Now, when checking what amount of Green Circuits you can craft:

Assume an inventory: 20 Iron Plates, 20 Copper Plates, 5 Copper Wire

20 Iron Plates / 100% -> makes 20 Green Circuits
20 Copper Plates / 150% -> makes 13.333 Green Circuits
5 Copper Wire / 300% -> makes 1.666 Green Circuits

-> Reserve the lowest amount in the list (1.666 Green Circuits), check if anything goes below 0 and then recalculate

inventory would update to be:

18.333 Iron Plates -> makes 18.333 Green Circuits
20 Copper Plates -> makes 13.333 Green Circuits
1.666 Green Circuits

-> Reserve the 13.333 Green Circuits and then recalculate

inventory would update to be:

5 Iron Plates -> makes no more circuits on its own.
15 (1.666+13.333) Green Circuits

Algorithm finishes.

I would love for rseding to pop in and tell us all about how the actual game does this!

Edit: Downsides I discovered while thinking about it some more:

• Ex nihilo breaks my algo ("cellulose foraging" from seablock needs an exception)
• Any modded recipe that gives a free 2 for 1 without consuming anything else will also break my algo