Replaces sharpe_ema (per-batch EMA, train) vs sharpe_annualised (val ×
sqrt(525600)) split. Single GPU kernel computes mean/std/sharpe via
2-pass block-tree-reduce; annualisation at the call site.
Per feedback_no_partial_refactor: consumer migration in metrics.rs /
training_loop.rs deferred to a follow-up commit; kernel + launcher land
in isolation first. Verified via 2 GPU oracle tests
(unified_sharpe_kernel_zero_mean, unified_sharpe_kernel_positive_drift)
passing on local RTX 3050 Ti (sm_86) in 1.78s.
Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>
3667cd1b04