Two week update. A student from DS's Algebra II class claims that the teacher is announcing to his former class that he has gone from being the smartest kid in Alg II to the smartest kid in Precalc. DS and I both hope and pray that the student (whom I think is the known hyperbolic type) is exaggerating. Nonetheless, the math teacher has urged DS to apply for USAMTS. DS is skeptical, and very worried that he is hearing about this only 3 days before the fisrt deadline, but he is also irresistibly drawn to puzzling through the problems, so we will see if he decides to make a stab at it.
At the same time, he is actively seeking out answers and support at school when he has issues with his homework (I couldn't refresh myself on synthetic division fast enough to help guide him through an exercise that was getting an unexpected answer, so he opted to ask for help at school -- and came back having clarified and solidified the concept!) THIS above all is the outcome I'd have hoped from this shift.
I'm feeling more zen again. We'll cross future math and other subject acceleration bridges when we come to them. For now, I love seeing this kid mature. Surprises at every step.