Wire route_exposure_to_factored() into both select_actions_batch_gpu
and select_actions_batch GPU paths, eliminating per-item CPU routing.
Previously, exposure indices (0-4) were downloaded from GPU and routed
to factored indices (0-44) one-by-one on CPU via route_action(). Now
the exposure→factored mapping runs entirely on GPU via the routing
kernel, with a single batch readback of the final factored indices.
Branching DQN path unchanged (already produces factored indices 0-44).
Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>
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