SECOND race condition from block_dim (1,1,1)→(32,1,1) change:
c51_loss_reduce had 32 threads all computing sum and writing to
total_loss[0] simultaneously. On sm_90 (H100) → corrupted loss →
NaN in C51 gradient → graph_mega replay hangs.
This kernel runs INSIDE graph_mega (submit_forward_ops_main),
called twice (MSE reduce + C51 reduce). Both corrupted.
Also fixed stochastic_depth_rng in previous commit (same issue,
runs in pre-replay).
Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>
ca7dfa9f08