Function constraint_matches 

pub fn constraint_matches(row: &OwnedRow, c: &Constraint) -> bool

True if row satisfies every (col, value) pair. Uses values_equal (null ≠ null — SQL/join semantics), matching the JS constraintMatchesRow (constraint.ts:17). Not compare_values (which treats null == null): a constraint value of null can never match (and joins never produce one — build_join_constraint returns None on null, §3.8).