Thanks for the further comments.

RE: hand luggage only - I will think about this and see if it's doable with a large carry-on. I'm taking a lot of gifts out for a birthday party, so I suppose I can get a disposable bag for the outbound and then just leave it. But I'm not sure I can get everything else into a carry-on. I will think about it.

RE: interlining - understood - the only experience I recall about interlining between two alliances with two separate tickets was CX (departing from IAD), connecting in HKG to TG (continuing on to BKK). They did it without a problem, but I know that's not a rule. I lucked out with non-American agents at a US airport who wanted to be helpful. They even tried to print the TG boarding pass for BKK-HKG, but failed. So I am cautiously hopeful. Chucking money at them is a last resort, and your post makes me think I'll get a Balinese friend to come with me up to check in to make sure the chucking is conducted in a culturally sensitive and appropriate manner while I look perplexed, anguished, apologetic and immensely grateful for any help they can provide.

If I end up having to sit on a UA flight for 12+ hours in Y, I am resigned to this. I will survive.