I would like to ask a couple of questions to clarify the situation in case other forum members are in a similar situation in the future.
Is there a difference between a SWU vs miles+copay upgrade? It seems OP was on the upgrade list with a SWU, so the GA could have upgraded him automatically and had the BP waiting for him when he arrived at the gate. However if OP was using miles+copay, does the GA need to swipe a credit card for the copay porition?
Also if OP was at the AC at CDG, could he have been in touch with the AAngels and inquired about the upgrade? Can the AAngels upgrade the passenger and process the SWU and/or collect the copay if using miles+copay? At what T-departure time, does the AC staff no longer have access to the upgrade list? And does this vary between US hubs and airports outside the US (e.g. CDG)?
Typically they say international flights start boarding 45 minutes prior to departure time. So I usually try to leave the AC or another lounge with enough time to get to the gate by that time. Another member here stated he/she arrives at the gate 75-90 minutes before the departure time. Is this recommended at an airport outside the US and/or if you are waiting for an upgrade and do not want to miss being called? If you are at the AC, doesn't the AC scan your BP and know that you are waiting at the AC and not at the gate?
I am sorry to hear the OP went through a very frustrating experience. However I wonder if the rest of us can learn from this instance and be better prepared if we also are in a similar situation in the future.