Phase B4b-2 introduced `exp_aux_to_label_per_sample` sized
`[alloc_episodes × alloc_timesteps]` (no cf-mult expansion — the
B4b-1 per-step kernel only writes the on-policy half). The batch
finalisation cloned into the emitted `aux_outcome_labels` with size
`total = base_total × 2` (cf-mult expanded), so
`dtod_clone_i32(src, total, ...)` invoked `src.slice(..total)` on a
half-sized source → `CudaSlice::try_slice` returned `None` → the
internal `unwrap()` panicked at cudarc safe/core.rs:1648.
Repro: workflow train-xzv56 panicked after rollout completed
(timestep=999) on fold 0; rollout itself ran clean, the OOM from
the prior commit is gone.
Fix: replace the single `dtod_clone_i32` with a 3-step build:
1. alloc_zeros::<i32>(total)
2. cuMemsetD32Async(ptr, 0xFFFFFFFFu32, total, stream) — fills
all `total` slots with i32 mask sentinel -1 (byte pattern
0xFFFFFFFF reinterprets as i32(-1))
3. memcpy_dtod the first `base_total` real labels from
exp_aux_to_label_per_sample into the on-policy half
CF half remains at -1. The K=3 sparse-CE loss masks `label == -1`
out of the mean and B_valid count, so CF samples contribute zero
gradient — exactly the semantic we want (CF actions have no
observed trade-close outcome to predict against).
Lib suite: 1016/0 green. Audit doc updated.
Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>
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