The liquid_tau_rk4_step kernel modelled f(x) = (1/tau)*(1-x), which has
fixed point x=1.0 for any tau. liquid_mod_buf was initialised to [1.0;4]
and the dynamics could never move it away from that fixed point since every
kernel call reduces to f(1.0)=0 (no perturbation path exists). The
velocity_mod multiplier in c51_grad_kernel was therefore always 1.0 — a
mathematical identity with zero measurable effect on spread_scale.
Additionally, no ISV slot existed for liquid_mod (violates §4.C.6
GPU-drives spec), and the associated LiquidTrainableAdapter supervised
path was never wired into the DQN backward pass.
Decision C (delete): remove liquid_tau_rk4_step kernel (experience_kernels.cu),
liquid_mod param + velocity_mod line (c51_grad_kernel.cu), liquid_mod_buf
allocation, liquid_tau_rk4_kernel field, update_liquid_tau() method and its
call site in update_eval_v_range() (gpu_dqn_trainer.rs). per_branch_q_gap_ema_buf
is retained — it is used independently for trajectory backtracking state
snapshot/restore. Supervised LiquidTrainableAdapter unchanged.
cargo check -p ml: 8 warnings (baseline), 0 errors.
Audit docs updated: dqn-wire-up-audit.md + ml-supervised-to-dqn-concept-audit.md.
Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>
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