Quality-review follow-ups to commit 97f1d25f5:
1. CRITICAL: preserve regression sentinel for slots 24, 25, 26, 32.
The post-clamps in apply_iqn_trunk_gradient + launch_cublas_backward_to
ran BEFORE run_nan_checks_post_backward, silently zeroing the buffers
the diagnostic was supposed to observe. Fix: inline check_nan_f32 calls
IMMEDIATELY BEFORE each launch_clamp_finite_f32 — same pattern as the
existing slot 35 check at line 6949. Now the diagnostic fires on NaN
entry; the clamp then sanitizes (preventing propagation but preserving
the flag — flags are sticky/OR'd in dqn_nan_check_f32, never cleared).
2. CRITICAL: correct F0 paper-review line reference + reasoning. The
commit body cited "5.0 norm-clip at line 16747" — that's a memset, not
a clip. Real norm-clip lives at lines 16827-16868. Also tightened the
L2-vs-per-element reasoning: L2 norm <= 5.0 worst-case bounds per-element
|x| <= 5.0 (single-element edge), still several orders of magnitude
below the 1e6 max_abs guard.
3. Inline comment at line 6951 mislabeled the clamp target as 'slot 27
input' — actually clamps the slot 35 buffer (bw_d_h_s2 post-DtoD). Fixed.
4. Articulated pre-clamp rationale: defense-in-depth regression protection
for input buffers (slots 24, 25, 35) against future pathologies that
could create extreme-but-finite inputs. The F1 ep2 NaN was outputs
overflowing finite inputs, but the same fix template covers both
failure modes per feedback_no_partial_refactor.
5. Renamed clamp_finite_f32_kernel -> dqn_clamp_finite_f32_kernel for
consistency with sibling utility kernels (dqn_nan_check_f32,
dqn_zero_kernel, dqn_grad_norm_kernel).
Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>
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