Graph recapture ruled out as NaN cause (NaN persists without graph
invalidation). Now testing: does NaN disappear when IQN is disabled?
If yes → IQN backward/Adam produces NaN on H100.
If no → NaN is in the main C51/MSE pipeline.
Also reverts graph invalidation hack from previous diagnostic commit.
Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>