The compute_expected_q and quantile_q_select kernels read per_sample_support[i*3+0/1/2]
(3 floats per sample), but the experience collector was passing eval_v_range_ptr which
is only 2 floats (v_min, v_max). Every sample after sample 0 read out of bounds.
Replace the u64 pointer field with a proper CudaSlice<f32> buffer [alloc_episodes, 3]
that is tiled with [v_min, v_max, delta_z] once per epoch via update_per_sample_support().
Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>
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