After a month of email back and forth, I have now received this from CO:
I forwarded your email to our Training department for clarification on valid tickets
for mileage credit on Alaska Airlines. They have confirmed that our agreement with Alaska Airlines does not include mileage credit for tickets issued in "A" class. If Alaska Airlines Mileage Plan allows credit of these
types of tickets, it is at their discretion. Their mileage plan is separate from the OnePass program and may have different terms and conditions.
Incredible. As far as I can work out, CO won't even speak to AS about it. They just keep quoting from pieces of paper. Any suggestions, anyone? What the hell do you do when the airline you're flying on says the miles will be credited, but the one whose programme you're using refuses?