Wow. Sorry to hear.

I think jiejie and 889 has covered the whose to blame bits but I wonder if Expedia issued the tickets as all AA stock (ie was your CA segment also issued under AA stock or did Expedia sell you two tickets?)

Anyway I will be reluctant to go trans-alliance on the same booking unless there's a very very big incentive to do it.

Your descriptions of how you were handled by AA and the PEK immigration authorities do not alter my generally negative predisposition towards them, as a non-guanxi counterparty.