Scottish Child Payment and Healthy Start are household benefits but missing from government spending #2338

What happens

scottish_child_payment and healthy_start_vouchers are in HOUSEHOLD_BENEFIT_VARIABLES (policyengine_uk/variables/household/income/household_benefits.py) but not in GOV_SPENDING_VARIABLES (policyengine_uk/variables/gov/gov_spending.py). Households receive them, but government spending doesn't count them.

On certified uk-data 1.58.0, the CI workstream measured these as about £0.52bn (Scottish Child Payment) and £0.05bn (Healthy Start) a year. gov_balance is therefore overstated by about £0.57bn a year.

The reverse holds for pawhp: it's in GOV_SPENDING_VARIABLES but not HOUSEHOLD_BENEFIT_VARIABLES. Open PR #2047 addresses that.

Fix

Add both variables to GOV_SPENDING_VARIABLES. Then add a code-health test that every household benefit funded by government is in government spending, with an explicit, reviewed exception list.

Found by the Autumn Budget 2026 CI work. The fiscal-partition check is in #2335.