Phase B commit 1 (cfc_step block-per-batch refactor) updated the
TRAINING-path cfg_cfc to grid=(B,1,1) but missed the same change in
evaluate_batched. The eval path silently kept the legacy grid=(1,1,1)
launch config, which against the refactored kernel meant only block 0
ran — batches 1..B-1 got GARBAGE h_new (whatever was in scratch
memory), which propagated through CfC + GRN to produce garbage probs,
which BCE-eval'd to chance-level AUC.
Caught by t6z89-vs-txftz cluster A/B at L40S:
baseline (t6z89, pre-Phase-B): mean_auc=0.7428 / h6000=0.7211 @ E0
broken (txftz, Phase B): mean_auc=0.4973 / h6000=0.5136 @ E0
train_loss matched within noise (0.6232 vs 0.6258) — the smoking gun
for "training works, eval is broken".
Why the perception_overfit smokes didn't catch it: those tests check
that loss converges on a synthetic up-ramp signal, exercising only the
training path. Eval is exercised by `evaluate_works_after_*` smokes
but those use n_batch=1, where grid=(1,1,1) and grid=(B,1,1)=(1,1,1)
are bit-identical — the bug only manifests at B>1.
Fix: eval cfg_cfc → grid=(b_sz, 1, 1), matching training. Plus an
explanatory comment so future eyes don't repeat the mistake.
Phase B perf gains are unchanged (training path was correct). Only
eval's wall time may grow slightly because of the now-correct
per-batch parallelism doing the work it should have done.
Follow-up: re-submit cluster A/B vs t6z89 to confirm AUC trajectory
recovers to ±0.005 of baseline.
Co-Authored-By: Claude Opus 4.7 <noreply@anthropic.com>
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