I mean, the cold milk will stay plenty cold (maybe it helps that I use a cup)

if you set it up (put it in a cup) then have the rest of your breakfast first and then have it last, that’s usually enough time for the coffee to dissolve. (Or if you prepare before taking your morning shower)

It dissolves alright. Some stirring, some waiting

I do this every day… It’s nice. More milk in my coffee.