IQN head now runs in parallel with C51 on every step:
- Constructs IqnHead in IntegratedTrainer::new()
- Per-step: samples tau ~ U(0,1), forwards h_t through IQN,
computes expected Q via tau-mean reduction
- Per-replay: forwards sampled_h_t through IQN (verifying
the head runs on replay data)
- Adam optimizers allocated for 4 IQN weight tensors
Not yet wired: IQN loss/backward, target soft update, ensemble
action selection. IQN runs forward-only — its Q values are
computed but not yet consumed for action decisions or gradient.
Local smoke: 100 steps, no crash, l_q=2.30 with both heads active.
Co-Authored-By: Claude Opus 4.7 <noreply@anthropic.com>
450eaab7f1