Is there some way to run the tapeout checks locally? Specifically, the Klayout MET density check? I'm doing trial/error in fixing this now, and upload/precheck/tapeout on efabless takes ~4 hours.

as far as I know, not yet. Do you get the density check fixed with the suggestion from @Dinesh A?

Working on it... I did notice

set ::env(CELL_PAD_EXCLUDE) {sky130_fd_sc_hd__tap* sky130_fd_sc_hd__decap* sky130_fd_sc_hd__fill*}

in the final config.tcl as well, does the new sky130_ef decap cell need to be added to that list?