DQN hyperopt walk-forward eval collapsed to 1 trade when Q-values were
nearly uniform (greedy argmax always picked the same action). Replace
batch_greedy_actions with batch_softmax_actions using the Gumbel-max
trick (argmax(Q/T + Gumbel(0,1))) — fully GPU-resident, no CPU
softmax/sampling. Temperature 0.1: nearly greedy when Q-values are
separated, diverse when uniform. Logs unique_actions/45 per backtest.
Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>
c10340708f