Migrates the magnitude-branch's direction-Q conditioning input to the
SP17 mean-zero contract. mag_concat_qdir builds a per-(sample, action)
softmax over V[z] + A_dir[a, z] across THREE inner passes (max,
sum_exp, E[Q]); all three now read `dir_logits_b[..] - a_mean_per_atom[z]`.
Without this migration the magnitude trunk-input would see raw E[Q_dir]
while c51_loss/c51_grad backward consumes centered A — mixed contract
ruled out by `feedback_no_partial_refactor`.
The Plan-4 q_rms adaptive scale (ISV[96]) is preserved unchanged;
centering changes the per-action E[Q_dir] values that feed it but the
scale formula itself is structurally orthogonal. Backward into the
direction logits flows through c51_grad (already mean-zero) so no bw
change is needed in this kernel.
GPU oracle test: B=1, SH2=2, NA=3, B0=4 with the same synthetic where
mean_a = [0.75, 0, 0.75] is non-zero. Asserts:
(a) h_s2[0..SH2] copied verbatim into concat prefix
(b) tail slots = centered_E[Q_dir] × (1.0 / q_rms) to ε=1e-5
(c) tail[0] < 0 / tail[3] > 0 sign asymmetry (regression detector)
Verification (RTX 3050 Ti):
cargo check --workspace → clean
cargo test sp17_dueling_oracle_tests --features cuda
-- --ignored → 4/4 PASS
⚠ INTERIM STATE: Thompson direction-select + aux-CQL barrier/ib still
read raw advantage. Commits C-D close them; Commit E annotates the two
already-centered c51_loss/c51_grad pre-SP17 sites.
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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