Bisect cut #1 (train-6zbcn) DEFINITIVELY identified Step 8/11 as the
NaN source. With launches disabled, q_var/q_by_action/v_a_means all
CLEAN. Forward atom-shift kernels confirmed innocent.
Defensive fix (belt-and-suspenders):
1. c51_aux_dw_kernel: clamp NaN/inf total to 0 at dW write site.
2. adam_w_aux_kernel: early-return if any input non-finite.
3. compute_expected_q: guard w_aux[a] read with isfinite (in addition
to state_121).
Together these prevent any NaN propagation through atom-shift
regardless of where the upstream NaN originated.
Step 8/11 launches RESTORED in submit_adam_ops. The underlying NaN
source is still unidentified but defensively neutralised. Smoke
verification next.
Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>
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