So-oo-oo-oo apparently my dog has pancreatitis, which is why he periodically chucks up white foam.
According to the vet it's because he's eating too much fat (... somehow?), so basically he's on low fat kibble and chicken-and-rice forever.
He's also on a bunch of medications which, as you can imagine, he "loves" taking, so yay for the twice daily wrangling to get his medicated slurry squirted into his mouth...