Single source of truth for the multi-horizon BCE per the new
feedback_single_source_of_truth_no_duplicates pearl. Eliminates the
`bce_loss_multi_horizon_sigma.cu` / `loss_sigma.rs` duplication
introduced earlier today and folds the Kendall σ-weighting into the
canonical kernel.
Deletions:
cuda/bce_loss_multi_horizon_sigma.cu (folded into legacy)
src/trainer/loss_sigma.rs (helper merged)
tests/bce_sigma_numgrad.rs (subsumed)
Rewrites:
cuda/bce_loss_multi_horizon.cu — replaced with σ-aware
implementation; kernel function name kept as
`bce_multi_horizon_forward_backward` so cubin symbol stays stable.
NVIDIA-grade warp-shuffle reduce (4 warps, 1 cross-warp barrier);
new args `log_sigma_h` (per-horizon Kendall σ logarithm) and
`d_log_sigma_h` (its gradient).
src/trainer/loss.rs — standalone helper updated to new 11-arg
kernel signature. Exposes optional `log_sigma_h` in `BceInput`
(None → zeros / passthrough Kendall init) and returns
`mean_bce_per_h` + `d_log_sigma_h` in `BceOutput`.
tests/bce_grad_finite_diff.rs — adds `log_sigma_h: None` to the
test inputs; all 4 numgrad tests PASS unchanged.
build.rs — drops `bce_loss_multi_horizon_sigma` entry from
KERNELS. The single canonical `bce_loss_multi_horizon` cubin
now contains the σ-aware kernel.
Wiring:
PerceptionTrainer gains a single `pub mha: MultiHorizonAttention`
field. Owns `log_sigma_h_d` + `grad_log_sigma_h_d` (and the rest
of the multi-horizon attention path, anchored on Stage 2 to fully
replace the legacy `attention_pool` path).
step_batched + evaluate_batched BCE callsites now thread
`mha.log_sigma_h_d` and `mha.grad_log_sigma_h_d` through the
11-arg kernel signature.
This commit keeps the legacy `attention_pool` callsite in place; the
Stage 2 commit will replace it with `mha.pool` + `mha.inv_pool` +
`mha.moe` and delete the `attn_*` fields entirely.
Verified locally: ml-alpha builds clean with the cuda feature,
bce_grad_finite_diff (4/4) PASS on RTX 3050.
Co-Authored-By: Claude Opus 4.7 <noreply@anthropic.com>
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