User directive 2026-05-17: borrow TFT GRN over the planned 2-layer MLP heads.
GRN structure: 2-layer GELU MLP body (eta_2 → eta_1) + GLU gate + main +
skip-projection from trunk → final sigmoid. Gives per-horizon "linear vs
deeper-transform" gating, matches the regime-conditional alpha pattern
(pearl_snapshot_alpha_is_regime_conditional). 5x parameter count vs the
2-layer MLP but the gated residual is exactly what TFT empirically wins on.
Phase 2C (TGN Δt Fourier features): 8 sin/cos features of Δt at log-spaced
periods [60s, 6s, 600ms, 60ms] appended to snap_features. Critical with
decision-stride>1 where Δt varies across positions. Bumps FEATURE_DIM 32→40.
Phase 2D (TFT VSN): per-feature softmax-normalised gates at the trunk entry,
replacing raw concat of snap_features. Learns to down-weight noisy
features per regime (canonical: trade-flow in low-volume, OFI in
spread-Q4). 2 new param tensors, 1 new cuda kernel (fwd+bwd).
Existing 2-layer MLP kernels from Tasks 1.3/1.4 stay in the cubin as
ablation baseline; wired path becomes GRN.
Phase 1.7 plan now spells out the full GRN forward + backward chain rule
(skip + sigmoid(gate) * main → outer sigmoid), kernel signatures,
parameter Xavier init, AdamW × 10 setup, and an extended numerical-grad
check covering all 10 new param tensors.
Co-Authored-By: Claude Opus 4.7 <noreply@anthropic.com>
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