Found by V7-gem audit: predictive_coding_loss kernel existed (forward only,
per-sample MSE on consecutive trunk activations), and compute_predictive_coding_loss
Rust wrapper existed, but no backward and no caller. Pure scaffolding.
Self-supervised temporal smoothness on the enriched trunk h_s2 IS in the
"better form" by the V7 methodology — it operates at the gradient level on
the network representation, not as a reward shaping term. Worth wiring up.
Three changes:
1) New CUDA kernel `predictive_coding_backward` (experience_kernels.cu)
Loss: L = sum_{i=0..N-2} (lambda/SH2) * sum_j (h[i,j] - h[i+1,j])^2
Grad: dL/dh[i,j] = (2*lambda/SH2) * sum-of-affected-loss-terms
Each h[i,j] appears in TWO loss terms (interior i): "current" of term i
and "next" of term i-1. Boundaries (i=0, i=N-1) have one. Closed-form
gradient written directly with no atomicAdd — one thread per (sample,
feature) cell, each writes to a unique slot, plain += accumulates into
bw_d_h_s2. Bit-deterministic.
2) Rust glue (gpu_dqn_trainer.rs)
- Load `predictive_coding_backward` kernel via existing exp_module_for_mag
- New field on DQNTrainer (predictive_coding_backward_kernel)
- Extend `compute_predictive_coding_loss` to also launch backward as
step 3 (after forward + reduce). Now the function name accurately
describes what it does — both compute and accumulate gradient.
3) Integration (fused_training.rs::submit_aux_ops)
Inserted the call right after `launch_recursive_confidence_backward`,
before regime_scale_td_errors. Both spots accumulate into bw_d_h_s2 via
plain +=, so ordering is irrelevant for correctness — what matters is
that this runs INSIDE the aux_child CUDA-graph capture window AND
BEFORE the trunk W_s2 → W_s1 backward GEMMs read bw_d_h_s2.
Why not also G6 (branch_independence) and G10 (temporal_consistency)?
Per V7-gem methodology — check for redundancy first:
- G10 wants Lipschitz on Q for similar states. Spectral normalization
(already wired on all 12 weight tensors) achieves *global* Lipschitz.
G10 adds *local-pair* Lipschitz on top. Possibly redundant — needs
a measurement before wiring blindly.
- G6 wants the 4 advantage branches to stay diverse. NoisyNets already
adds different parameter noise per layer → naturally diverse heads.
Ensemble KL gradient pushes ensemble heads apart (different mechanism
but similar intent). Possibly redundant for the 4-branch case.
G12 is unambiguously useful — trunk smoothness is a genuine gem with no
existing equivalent in the codebase. G6/G10 land separately if measurement
shows they add real value beyond spectral_norm + NoisyNets + ensemble KL.
Files touched:
crates/ml/src/cuda_pipeline/experience_kernels.cu (+45)
crates/ml/src/cuda_pipeline/gpu_dqn_trainer.rs (+33 / -3)
crates/ml/src/trainers/dqn/fused_training.rs (+9)
Verified: cargo check passes. Smoke test running to verify training is
stable with G12 active (lambda_pred=0.1 — small enough that any regression
is from a real bug, not dominance over the C51/IQN gradient).
Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>
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