Hey, ran into an issue with stone furnaces and the coke recipe. Since raw coal is both the fuel and the ingredient for coke, if ore supply dips and coal is still coming in on the belt, inserters will start processing coal into coke instead of waiting for ore to come back. The furnace silently switches jobs and you end up with a stalled smelting array and a pile of unintended coke.
Two possible fixes that come to mind:
1. Use crushed coal as the coke recipe input rather than raw coal — that way the ingredient and the fuel are distinct items and inserters can't confuse them
2. Allow furnaces to have a recipe locked in (like assemblers can), so the player can tell a furnace it's an iron smelter and it won't switch to coke even if coal shows up
