Demonstrates the practical use case of the protocol — not as a post-hoc
audit but as an in-training abort condition. Walks through the existing
per-epoch trace and shows when the protocol would have triggered an early
stop on DFA training and what the saved compute would be.

Result: DFA on 4-block d=256 ResMLP fires diagnostic (b) at epoch 4 with
test acc 0.3076. The final acc at epoch 100 is *also* 0.3076 (identical).
Stopping at epoch 4 saves 96% of compute with zero headline acc loss.