like I could go more general but nothing feels quite right. The free monoidal category on a unital magma? prolly better but no longer carries the right emotional weight...
nah free monoidal category on a monoid is where it’s at imo. cute demonstration of the macrocosm principle plus it should work out to be something familiar, i worked this out awhile ago and totally forgot the answer
it's the augmented simplex category! this is really important it's what makes lots of stuff work, e.g. anytime you have a (co)monad you can turn it into a [co]simplicial endofunctor...