Sad. I was part of the team that spun up the original codesharing with Alaska, which evolved out of the interchange flights we had flying FAI-ANC-SEA-ORD-DCA (AA metal) and IAH-DFW-SEA-ANC-FAI (AS metal). Both airlines flew ex-Braniff 727-227's so it was easy to simply swap crews at SEA.
When the 727's were being retired, we had no choice but to work out the codeshare because the MD80 cockpits between AA and AS were so different, and neither union was wild about having another airline fly their airplanes lest it become scope creep...