My opponent's resignation caught me way off guard. I had only barely begun to switch my thinking from strategic to tactical — is this really a winning position for black?

Also, white (ranked hundreds of points above me) commented that perhaps 13.p11 would have been better. I guess I see it, especially if 13.o11 14.p13 leads to immediate resignation, but I think the situation is a bit over my head. Any comments would be gratefully accepted.

Well I certainly would have tried something. Maybe |15.i15 one branch is 16.h11 17.g11 18.f10 19.n15 20.m16 21.l16 22.k17 23.j17 24.i18 25.f18 26.g19 27.d19 28.f17 29.e16 30.e15 31.d14, or 16.g12 17.f12 18.e11 19.n15 20.m16 21.l16 22.k17 23.j17 24.i18 25.e18

I agree |13.p11 would have been much simpler for white. Then 14.p13 15.r12 and black is cut off. At the end of the game you are connected to the right. For example |15.r12 16.s12 17.t11 18.r14 19.u13 20.t15 or |15.s11 16.r12

Thank you so much David! It's really helpful to see these lines of giving up one side to cut your opponent off from the other. Very simple the way you string together two ladders to narrow the playing field. Going to have to look for opportunities to incorporate this strategy!