Root cause #1: Adam epsilon=1e-8 rounds to 0 in BF16 → sqrt(v_hat)+0 = sqrt(v_hat) → div-by-zero when v_hat≈0. Fix: adam_epsilon configurable, default 1e-3.
Root cause #2 (partial): compute_q_values produces NaN even with sync. NOT a race — the graph_adam's Adam kernel writes NaN to params in async mode but works in CUDA_LAUNCH_BLOCKING=1 mode. The Adam kernel has no shared mem / atomics / warps — it's per-element. The ONLY shared read is grad_norm_sq[0]. Investigation continues.
Added: adam_epsilon to DQNConfig, DQNHyperparameters, GpuDqnTrainConfig, dqn-smoketest.toml, training_profile.
Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>
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