Function promote 

pub fn promote(
    capability: &mut Capability,
    witness: &FullAdmissibilityWitness,
) -> Result<()>

Promote an allowed transition: one kernel transaction that decrements the call budget, debits the risk budget with exactly the certified increment, and records the spend (PSP-9 system 12).

Spending is monotone: later barrier decrease does not refund budget. A read-only check that never consumes budgets is not sufficient.