When crafting something in a large recipe tree, you're bound to have ingredients leaving your inventory as they get processed, especially if you're playing with mods. This causes that item and all of its branches on the tree to reappear in your synthetic favorites. I think there should be a system to let you know which items are there because you still need them and which ones are there just because you don't currently have them in your inventory. I'm not sure how this would be implemented, though. It could put a green background on those items, or make the number in green, but then what if you've only obtained some of that item and not all that you need? Of course one option is to never have them reappear but that could also get confusing.

I've been thinking about how to manage this for a while. There are a lot of concerns but one of the larger ones is how do you not mislead the player. I think simple optimizations would be beneficial in this regard, however. For instance, once you obtain all of a single item, never show that requirement again. This wouldn't track partial progress, but would be nice for situations where you bulk craft step 1, then shove it in a machine to process. I've also been considering monitoring the initial state of the target object. Say, you want to craft 6 ladders, but currently have 3 in your inventory. Should it start by considering you need only 3 more ladders? Or should it instead decide since you have 3 you need to make 9 total? What happens if you put those 3 away and now your synfavs ask you for 9? That'd be misleading. I think I'd want to make them track the minimum amount you've had in your inventory for the duration, and ignore that many. Say, you start with 3 ladders, it'll count up your inventory but ignore 3 ladders. If at any point you put 2 of those away, it'll only ignore 1 ladder from then on, even if you grab the 2 back. What do you think?

I think the way you described it sounds good, for example if I have 3 ladders in my inventory and want 6 more for a total of 9, then this is how I would expect it to work. This would also fix the issue of trying to craft something in less quantities than you already have in your inventory and it just doesn't do anything.

Actually just thought of another potential solution, that being to add an option such as a keybind to simply mark any ingredient as complete without it needing to be in your inventory. This could also help with fluids since those can never be in your inventory anyway.