I called COPA in Brazil this afternoon, they said there is a lounge.
Then when I asked what were the policies to enter, she
transferred me to an elite agent, but the call dropped
and couldn't get an answer.
I'll try again tomorrow.

Last time (March) when I went to the RCC at GRU, I just showed my
OnePass card. I don't recall showing my boarding pass.
Will try again in the next 2 weeks.