library("SpaNorm")
nbMuFloor()[1] 9.357623e-14
The polish engine floors every fitted mean at this value, and a caller that rebuilds the mean from polished coefficients (for inference, say) should floor at the same value, so both stages work on one mean function. It is a numerical guard against exp() underflowing to exactly zero, not a statistical clamp: exp(-30) is far below any mean the model can meaningfully estimate.
nbMuFloor()
exp(-30).