- Fix NaN detection: replace non-existent isnan() with ne(&self) (NaN≠NaN)
- C51 gradient strip: copy().detach() replaces to_vec2→from_vec GPU→CPU→GPU roundtrip
- GPU batch fast path: skip CPU fold + 5× from_vec when GpuBatch available
- Action validation: GPU clamp() replaces CPU loop in GPU batch path
- PER TD errors: keep as GPU Tensor when GpuPrioritized replay active
- PER indices: use GpuBatch.indices directly instead of CPU Vec→Tensor
- IS weights: cache GPU tensor from GpuBatch, reuse in both loss paths
- Logging: Q-values 10→500 steps, diagnostics 100→1000 steps
2758 tests pass, 0 clippy warnings.
Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>
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