docs(sp17): annotate c51_loss/c51_grad SP17 compliance (Commit E)
Audit-only commit per user design call DD9. The plan's Task 1.4
incorrectly claimed c51_loss_batched + c51_grad_kernel needed migration;
both kernels have been mean-zero centered since commit 56373f094.
Audit findings:
c51_loss_kernel.cu::c51_loss_batched (line 760-806):
- Forward dueling reduction at lines 765-779 already computes
`a_mean = (1/n_d) Σ shmem_adv[a, j]` and applies
`centered = shmem_adv[a_d, j] - a_mean` — IS the SP17 mean-zero
projection. Annotated `/* SP17 mean-zero */`.
- Counterfactual magnitude path at lines 788-805: same pattern.
- Spectral decoupling at lines 812-827: same pattern.
- Bellman target argmax at lines 848-855: shmem_proj[j] IS a_mean_per_atom.
- Per-d=1 magnitude std normalization (line 770-778) is ORTHOGONAL to
SP17 mean-zero — a separate variance-control concern for the magnitude
branch's tighter Q distribution. Annotated
`/* SP17: per-d=1 mag std normalization (orthogonal) */`.
c51_grad_kernel.cu::c51_grad_kernel (line 287-291):
- `dueling_grad = (a == a_d) ? (1.0f - inv_A) : (-inv_A)` at line 288 IS
the SP17 mean-zero Jacobian: J[a, a_d] = δ(a, a_d) − 1/n_d. The chain
rule for centered logit `A_taken − mean_a A` w.r.t. A[a'] produces
exactly this Kronecker-delta-minus-uniform pattern.
- Per-d=1 magnitude std grad multiplier (line 290) — same orthogonal
concern as c51_loss.
Zero code-path change. Both kernels behave bit-identically to pre-E.
Wire-up status (FINAL — every consumer SP17-compliant):
compute_expected_q (Task 1.2) MIGRATED
quantile_q_select (Commit A) MIGRATED
mag_concat_qdir (Commit B) MIGRATED
Thompson direction-select (Commit C) MIGRATED + V wired in
barrier_gradient_direction (Commit D) MIGRATED
ib_gradient_direction (Commit D) MIGRATED
c51_loss_batched (this commit) ALREADY-COMPLIANT, ANNOTATED
c51_grad_kernel (this commit) ALREADY-COMPLIANT, ANNOTATED
After this commit, EVERY advantage-logit read in cuda_pipeline goes
through the SP17 mean-zero contract. No un-centered raw-advantage reads
remain in production kernels.
Verification (RTX 3050 Ti):
cargo check --workspace → clean
cargo test sp17_dueling_oracle_tests --features cuda -- --ignored → 6/6 PASS
grep adv_a[ kernels (excluding centered/comments) → empty
grep dir_logits_b[ kernels (excluding centered/comments) → empty
Plan: docs/superpowers/plans/2026-05-08-sp17-dueling-q-network.md
Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>
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