FISH Shell - Cannot `cd -` when extending builtin cd

I have a custom cd function that looks like:

function cd -d "cd with auto conda activation"    # set -gx OLDPWD (pwd) <-- uncommenting this does not resolve issue    builtin cd $param $argv    if test -f (pwd)/.condaconfig        set -gx CONDACONFIGDIR (pwd)        conda activate (cat .condaconfig)    else if [ -n "$CONDACONFIGDIR" ]        if [ -n (string match -q -- "*$CONDACONFIGDIR*" (pwd)) ]            set -gx CONDACONFIGDIR ""            conda deactivate        end    endend

but with this active, I cannot use cd - to change to the previous directory.Have I implemented builtin wrong? I feel like I'm missing something here.

I have an equivalent custom function in bash which works fine and continues setting/using OLDPWD - fish seems to use something else to keep track of previous directory, but it's not an environment variable (ie. doesn't show up in the output of env)