When playing with Carbonut Agriculture, you can soft-lock yourself on Vulcanus if you didn't have Coal Synthesis unlocked before going there. This is especially problematic if you use Any Planet Start or Planet Picker to start there.

Carbonut Coal Synthesis adds a simple trigger technology locked behind Carbonut Agriculture, Calcite Processing, and Sulfur Processing that grants the usual Coal Synthesis recipe; this way it's not an immediate unlock, and also won't trigger on other planets.