Constant RELATIONSHIP_COLUMNS 

const RELATIONSHIP_COLUMNS: [&str; 18];

The projected columns of semantic_relationships, in order. Every derived branch and the declared-edge branch must project exactly these so the top-level UNION ALL type-aligns; build_relationships_plan re-selects them over the union to enforce the contract. (The physical declared table additionally stores valid_from/valid_until, which feed the validity filter and the projected window columns.)