Function boolean_split_operands 

pub fn boolean_split_operands(
    first: &BrepSolid,
    second: &BrepSolid,
    options: &BooleanOptions,
) -> Result<(BrepSolid, BrepSolid), KernelRefusal>

The two operands a binary boolean’s arrangement reads: prepared as the boolean prepares them, with every boundary edge split where the imprint’s sections meet it. These are the NNN-first and NNN-second stages BREP_BOOLEAN_DUMP writes, not the operands at the boolean’s entry.

A boolean must read the same on these as on the operands it split them from: the splits are vertices its own imprint puts on those edges anyway. Where it does not, an imprint lane is deciding on what the input happens to have split, and that is a defect.