# UTFANSWF v21 — Row 20 SN Offset/Pivot Probe

**Context:** DIAGNOSTIC_NON_GATING. No physics, thresholds, datasets, parameters, or gate verdicts changed.

## Existing SN nuisance

```json
{
  "SN_M_fit_existing_offset": 2.115928369672133
}
```

## Raw SN nodes

| Slice | z | residual | sigma | pull | chi2 |
|---|---:|---:|---:|---:|---:|
| SN mu z=0.10 | 0.100 | 0.177029 | 0.200000 | 0.885146 | 0.783483 |
| SN mu z=0.35 | 0.350 | -0.589104 | 0.223607 | -2.634554 | 8.445196 |
| SN mu z=0.70 | 0.700 | 0.334483 | 0.244949 | 1.365521 | 1.864647 |

## Global offset removal

Global residual offset removed: `-0.025864`

| Slice | recentered residual | recentered pull | recentered chi2 diag |
|---|---:|---:|---:|
| SN mu z=0.10 | 0.202893 | 1.014466 | 1.029141 |
| SN mu z=0.35 | -0.563240 | -2.518887 | 6.344790 |
| SN mu z=0.70 | 0.360347 | 1.471110 | 2.164166 |

## Endpoint offset removal

Endpoint residual offset removed: `0.255756`

| Slice | endpoint-recentered residual | endpoint-recentered pull | endpoint-recentered chi2 diag |
|---|---:|---:|---:|
| SN mu z=0.10 | -0.078727 | -0.393634 | 0.154948 |
| SN mu z=0.35 | -0.844860 | -3.778330 | 14.275778 |
| SN mu z=0.70 | 0.078727 | 0.321401 | 0.103299 |

## Pivot geometry

| Quantity | Value |
|---|---:|
| raw pivot residual | -0.831739 |
| raw pivot pull | -3.719650 |
| global-recentered pivot residual | -0.831739 |
| global-recentered pivot pull | -3.719650 |

## Interpretation

- This probe removes global SN offset structure and tests whether the z=0.35 pivot survives.
- The z=0.35 pivot survives global recentering; it is not explained by the existing nuisance offset alone.
- The pivot curvature is invariant under a global additive SN offset, as expected.

## Verdict

SN_pivot_survival_under_offset_probe_complete; diagnostic only; no physics, thresholds, datasets, parameters, or gate verdicts changed.
