Changed per_prefix_scan, per_sample, and is_weights_f32 kernels to accept
size as a const int* pointer (pinned device-mapped) instead of a baked int.
Graph replay now uses the CURRENT buffer size, not the capture-time value.
Host updates the pinned size on every insert_batch and clear.
per_sample also reads rng_step from pinned pointer (GPU-side increment).
Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>
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