Smoke smoke-test-dr2bn (commit 19b008e1c) failed all 7 SP1 pass criteria.
F1 first-fire signature at step 240: flagged=[6=grad_buf, 12=save_h_s2,
26=iqn_trunk_m, 32=bn_d_concat_buf] — IDENTICAL to pre-fix smoke-xvzgk
but at step 240 vs 890. The surgical fix at 19b008e1c made F1 NaN
EARLIER, not prevented it.
Diagnosis: the ε floor `(1e6 * isv).max(1e3)` clips legitimate F1
startup gradients to ±1e3 when fold-boundary ISV reset puts ISV[96]
or ISV[21] near 0. Clipped gradients destabilize Adam EMAs → cuBLAS
GEMM accumulator overflow → slot 26 + 32 NaN.
F0 regression unchanged across Phase C (35.24 vs pre-fix 34.55).
Confirms the F0 regression is a Phase B instrumentation side effect,
not Phase C. Separate investigation thread within SP1.
Next iteration: Task 6 fix-up #2 changes ε floor to `(1e6 * isv.max(1.0))`
guaranteeing max_abs ≥ 1e6 regardless of ISV state. Removes cold-start
clamp pathology while preserving F0 paper-review intent.
0c99e08002