Function accept_sound_against_scoped 

pub fn accept_sound_against_scoped(
    inputs: &[&BrepSolid],
    solid: BrepSolid,
    entry: &str,
    candidates: &FxHashSet<u64>,
) -> Result<BrepSolid, KernelRefusal>

accept_sound_against reading only the faces in candidates: the faces the operation built or changed, their neighbours, and every face whose box reaches the other operand. A face outside that set is an operand’s own, untouched, and lies clear of everything the operation added, so a crossing on it was the operand’s and passes through exactly as the full scan passes it (the inputs are scanned, flagged, and the result returned). An empty set is a result with nothing to scan. A flagged subset hands the whole result to the full acceptance, so every repair and refusal reads as before. (BooleanOptions::untouched_passthrough)