Function validate_bus_set 

pub fn validate_bus_set<'a, I>(endpoints: I) -> Result<()>
where
    I: IntoIterator<Item = (&'a str, &'a PermutationCheckSpec)>,

Every multi-endpoint Permutation bus_id must have at least one endpoint owning a real RowIndexLeBytes/RowIndexByte clock; otherwise label-only stitching admits char-2 parity collapse.