Removes 3 panic gates inserted by 2c.3a:
- BatchedBackward::backward_full
- gpu_dqn_trainer::apply_iqn_trunk_gradient
- gpu_dqn_trainer::apply_ensemble_diversity_backward
GRN backward chain (per block, mirrors encoder_forward_only):
d_y → backward_raw_phase1 (LN_dx + LN_dgdb + GLU_bwd)
→ cuBLAS Linear_b dW + dX
→ backward_raw_phase2 (ELU_bwd)
→ cuBLAS Linear_a dW + dX
→ for h_s1: Linear_residual dW (no_bias_lda) + dX accumulation
→ for h_s2: saxpy_inplace identity residual into d_h_s1
New helper: BatchedForward::encoder_backward_chain orchestrates both
GRN blocks. Used by main backward (writes to grad_buf), CQL backward
(writes to cql_grad_scratch), and the two auxiliary paths (write to
iqn_trunk_m then SAXPY into grad_buf).
apply_ensemble_diversity_backward additionally fixes value-head
indices: w_v1 4→13, w_v2 6→15 (legacy indices were post-2c.3a stale).
iqn_trunk_m grown from legacy 4-tensor size to 13-GRN-tensor padded
size (matches grad_buf layout for the trunk portion so the SAXPY
mix-in lands at the correct per-tensor offsets).
batched_backward::launch_dw_only_no_bias_lda added for Linear_residual
backward with padded states stride (Linear_residual has no bias, so
the bias-grad kernel cannot run with NULL db).
ReLU masks on h_s1 / h_s2 are gone — the GRN trunk ends in LayerNorm
which has no truncation derivative. Value-head FC retains its ReLU
mask (value head still uses ReLU activation).
launch_cublas_backward_to changed from &self to &mut self because the
GRN backward needs to scribble per-block partial-reduction scratch
inside grn_h_s{1,2}_online; the borrow split lets the trainer hand
&mut BatchedForward + &BatchedBackward to encoder_backward_chain.
Smoke validation (multi_fold_convergence, 3 folds × 5 epochs, 599.73s):
fold 0: best Sharpe 7.52 at epoch 2, val_Sharpe 0.51
fold 1: best Sharpe 60.94 at epoch 4, val_Sharpe 0.64
fold 2: best Sharpe 10.40 at epoch 2, val_Sharpe 0.82
All 3 dqn_fold{N}_best.safetensors checkpoints written. PF=5.29
on fold 2 epoch 5 with +988% return — gradients flow cleanly through
the GRN composition without NaN/Inf.
Audit doc updated (Invariant 7). // ok: suppressions added to 5
defensive null-guard sites in read_isv_signal_at /
read_atom_utilization / compute_q_spectral_gap (pre-existing,
documented in fn doc comments).
Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>
f94d857ebc