experience_action_select kernel now uses philox_uniform(episode_id,
timestep, call_counter) instead of stateful lcg_random(&rng).
Eliminates branching-dependent RNG state divergence across processes.
Also passed timestep to backtest evaluator's action_select launch.
Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>