`compute_adaptive_tau` (gpu_dqn_trainer.rs:7045) had zero production
callers — its q_div_ema field's doc-comment explicitly flagged it
"NOTE: only consumed by the orphan helper compute_adaptive_tau (zero..)".
Pre-SP3 attempt at adaptive-tau control, superseded by the SP3/SP4 ISV-
driven tau controller (`tau_kernel.cu` + ISV[TAU_INDEX]).
Removed:
- compute_adaptive_tau method (CPU EMA + ratio-scaled tau formula)
- q_divergence_readback method (only caller was compute_adaptive_tau)
- q_div_ema field + initialiser + fold-reset assignment
- q_divergence_pinned + q_divergence_dev_ptr struct fields, alloc, free
- q_divergence_dev_ptr memsets at C51 launch sites (2)
- q_divergence_dev_ptr arg in launch_c51_loss kernel call
- c51_loss_batched kernel parameter `q_divergence` (never written by
kernel body — comment "removed from hot path — zero atomicAdd"
confirmed buffer was inert; deleting parameter keeps kernel ABI clean
per feedback_no_partial_refactor)
- Stale doc-comments referencing q_divergence in c51 reduction kernel
- readback_pinned [12]=q_divergence layout doc (slot was never read)
cargo check clean. SP4 + state_reset_registry lib tests pass (11/11).
16/16 SP4 producer GPU tests pass on RTX 3050 Ti. No behavior change —
dead code only.
Refs: feedback_no_cpu_compute_strict sweep audit (commit 6a6b58aec)
flagged this as orphan; feedback_wire_everything_up mandates deletion.
Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>
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