76 households have negative VAT on 1.58.0 #565

What happens

On certified uk-data 1.58.0 (enhanced_frs_2024_25, sha256 5ba399ea…), 76 households have negative VAT under policyengine-uk main 6d89338.

The likely cause is negative imputed consumption in one or more VAT-bearing categories. That's unverified: it was measured, not traced.

Asks

• Find which consumption variables are negative for these households, and why the imputation or uprating produces negatives.
• Add a data test that imputed consumption is non-negative, so that VAT can't go negative for any household.

Found by the Autumn Budget 2026 CI work (aggregate-impact report, PolicyEngine/policyengine-uk#2335). Any fix lands with the next uk-data batch (d833).