American tries to shine such off by stating "American assumes no liability for articles carried in the passenger cabin."

Of course, that's rubbish and can be easily taken to small claims court if necessary. But I think I'd try to cover myself by requesting a statement on arrival, or taking the computer to baggage claim and attempting to document a claim at that time.

If not, I would take the computer to a computer repair station and request an estimate for repairs and get a statement of valuation for a similar computer (similar in terms of features, but also disclosing how old it might be) and prepare a claim with details of the flight number, date, time, name of FA and possibly others who could verify what happened.

It was undoubtedly a mistake - but an AA employee was responsible for this and AA should 'fess up and make it right - and as a requester, make it had for them to say "no". The complaints thread has some snailmail addresses if you choose to formalize this outside of the usual customer service channel - though you may ope to use that first.

Others may weigh in with some better ideas. I have never had anything like this happen on an airline (though one person attending a mandatory training / intervention I gave dropped half of a Coca Cola into my keyboard - I requested his name and department, telling him I would need to document this for my insurance company to reimburse me, and continued with the training; I found a replacement keyboard on eBay for $15, but I am sure the saboteur sweated for a while...)