cbn_diagnostics drives the extra legacy plc/cflux/cpool and soil-prop files. it used to be read from carb_coefs.cbn (now removed). it now maps to the hru_cb flag letter: "l" (layer) turns diagnostics on; "y" gives the light files only (hru_cbn_lyr, hru_seq_lyr, hru_n_p_pool_stat). write carbon in soil by layer write beginning of simulation soil properties headers to hru_begsim_soil_prop write end of simulation soil properties headers to hru_endsim_soil_prop write carbon in soil, plant, and residue write carbon variables headers to hru_carbvars write org_allo variable headers to hru_org_allo_vars write org_ratio variable headers to hru_org_ratio_vars write org_trans variable headers to hru_org_trans_vars basin carbon summary - only when the legacy soil carbon path is on