How worrying is damage to a carbon fiber frame near the bottom bracket? Last week on a ride my chain popped off the inner chainring and  managed to get stuck between the chainring and frame. I (probably foolishly) tried to work it free by yanking on the chain and that just got it wedged in harder. I took it to the shop and the repair guy is telling me that even though the damage looks superficial (there are some gouges near the bottom bracket where the chain rubbed against it), because it's a carbon fiber frame he can't guarantee that there won't be some major failure of the frame sometime down the road.

How concerned should I really be about this? I don't care about the cosmetic damage. How obvious will it be when/if the damage gets worse to the point of being a safety issue? Will there be telltale signs of a widening crack/tear that will give me some warning well ahead of time, or is there a risk of a random catastrophic failure?
I would be concerned. The bottom bracket is the most heavily stressed part of any bike, and carbon has a catastrophic failure mode--that is, you don't get any warning. One minute it seems fine, the next minute, you've got carbon-fiber shrapnel.

As a first measure, I might clean it up as best as I can, take some pictures, and send them to the manufacturer or the manufacturer's area rep to get their feedback.