The IQN readiness gauge on `GpuDqnTrainer` is a streaming improvement
fraction `(iqn_loss_initial - iqn_loss_ema) / iqn_loss_initial`
(gpu_dqn_trainer.rs:5805-5818). `iqn_loss_initial` is captured once on
the first `update_iqn_readiness` call where it is still ~0 and never
resets — across folds it stays pinned to the fold-0 epoch-1 IQN loss.
The pinned device-mapped readiness slot is read by `c51_loss_kernel`
as the CVaR α and by IQN gradient-weight gating, so a stale anchor
either pins readiness near 1 (over-confident, full IQN gradient
weight on a still-recovering head) or near 0 (under-weighting a
converged head).
Fix:
- New `pub fn reset_iqn_readiness_state` on `GpuDqnTrainer` zeroes the
three coupled scalars (iqn_loss_initial / iqn_loss_ema /
iqn_readiness) and writes 0.0 through the device-mapped pinned host
slot — no HtoD copy, the mapping propagates the host write directly.
- New `pub(crate) fn reset_iqn_readiness_state` wrapper on
`FusedTrainingCtx` mirrors the existing `reset_eval_v_range_state`
pattern.
- Three new `FoldReset` registry entries (`isv_iqn_loss_initial`,
`isv_iqn_loss_ema`, `isv_iqn_readiness`) dispatch through one match
arm in `reset_named_state` (training_loop.rs).
`update_iqn_readiness` already handles `iqn_loss_initial < 1e-12` as
the bootstrap branch, so the new fold's first batch is recaptured as
the anchor on the first call after reset, by design.
Per `feedback_no_partial_refactor.md` — same fold-boundary
state-migration contract, all three coupled scalars migrate together.
This commit completes the 3-fix sequence (Fix 1 IQN target sync,
Fix 2 aux Adam states, Fix 3 IQN readiness) closing the fold-boundary
contract gap surfaced by the audit. Bug signature being resolved:
F0 ep5 Q=+0.79 (healthy)
F1 ep1 Q=+0.82 (boundary fine; c51_alpha warmup blends IQN low)
F1 ep2 Q=+2.23 (drift starts — IQN online↔target gap widens)
F1 ep3 Q=+4.05
F1 ep4 Q=+10.66 (geometric ~2.3×/epoch)
F1 ep5 NaN at step 5 (fp32 overflow past atom support)
Fix 1 (IQN target sync) is the load-bearing fix for the geometric
drift itself; Fix 2 prevents first-epoch Adam-step overshoot in
seven aux optimizers; Fix 3 closes the gauge-staleness path.
cargo check -p ml --lib clean at 13 warnings (workspace baseline).
cargo test -p ml --lib --no-run clean. All three existing
`state_reset_registry::tests` pass without modification.
Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>
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