It isnt needed (we can switch it). Currently libstanc.a is being used here https://github.com/stan-dev/cmdstan/blob/develop/make/stanc#L107
As a two cents, I understand
.Renviron is part of the R installs on Mac OS X, so I don’t like removing it as the standard thing to do. The easiest thing to do might be to not build stanc2 in cmdstanr and sidestep the issue. That’s my motivation for asking about stanc2 here.