Delete every CPU fallback block across 14 files (-286 lines):
- dqn.rs: CPU replay buffer, tensor construction, PER fallback, gradient paths
- hyperopt/adapters/ppo.rs: CPU curiosity modules, trajectory generation
- hyperopt/adapters/dqn.rs: CPU backtest fallback, sync no-op
- trainers/ppo.rs: CPU training error stub
- l2_cache.rs: CPU stub functions (gate callers behind cuda too)
- replay_buffer_type.rs: CPU is_gpu_prioritized fallback
- validation/harness.rs: CPU regime breakdown fallback
- build.rs: cpu_only_build cfg (never referenced)
- evaluate_baseline.rs: CPU gpu_handled fallback
- testing/integration/gpu: CPU test stubs
Zero #[cfg(not(feature = "cuda"))] remains in the codebase.
Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>
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