# UTFANSWF v21 — Row 20 Coupled Bridge Test

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

## Original residual vector

| Node | Pull sigma |
|---|---:|
| CMB_ell_A | 4.411555 |
| BAO_H | 1.716363 |
| BAO_D_M | -1.268904 |
| SN_pivot | -3.719650 |
| SH0ES | -5.423077 |

## Coupled bridge result

| Quantity | Value |
|---|---:|
| original RSS | 8.201426 |
| original chi2 | 67.263396 |
| best bridge strength | 1.266000 |
| best RSS | 5.779190 |
| best chi2 | 33.399038 |
| RSS improvement | 2.422236 |
| status | coupled_bridge_feasible_strong |

## Best transformed residual vector

| Node | Pull sigma after bridge |
|---|---:|
| CMB_ell_A | 3.145555 |
| BAO_H | 0.450363 |
| BAO_D_M | -0.002904 |
| SN_pivot | -2.453650 |
| SH0ES | -4.157077 |

## Interpretation

- This test asks whether a single coupled bridge amplitude can reduce early/radial and late/transverse residuals together without flipping the layered sign structure.
- Best no-flip bridge strength is 1.266 sigma-equivalent.
- Original RSS 8.201 reduces to 5.779, improvement 2.422.
- A coupled-layer bridge remains mathematically feasible under sign-preserving constraints.
- This is a feasibility diagnostic only. It does not modify physics, thresholds, datasets, parameters, or gate verdicts.

## Verdict

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