def merge_nodes_and_transfer_edges(
    driver: GraphDatabase,
    surviving_id: str,
    deprecated_id: str,
) -> int:
    """
    Transfer all edges from deprecated node to surviving node,
    then mark deprecated node as merged.
    Returns the number of edges transferred.
    """
    with driver.session() as session:
        # Transfer outgoing edges
        result = session.run("""
            MATCH (deprecated:Entity {id: $deprecated_id})-[r]->(target)
            WHERE NOT target.id = $surviving_id
            MATCH (surviving:Entity {id: $surviving_id})
            CALL apoc.refactor.from(r, surviving)
            YIELD input, output
            RETURN count(*) AS transferred
        """, deprecated_id=deprecated_id, surviving_id=surviving_id)
        outgoing = result.single()["transferred"]

        # Transfer incoming edges
        result = session.run("""
            MATCH (source)-[r]->(deprecated:Entity {id: $deprecated_id})
            WHERE NOT source.id = $surviving_id
            MATCH (surviving:Entity {id: $surviving_id})
            CALL apoc.refactor.to(r, surviving)
            YIELD input, output
            RETURN count(*) AS transferred
        """, deprecated_id=deprecated_id, surviving_id=surviving_id)
        incoming = result.single()["transferred"]

        # Mark deprecated node
        session.run("""
            MATCH (e:Entity {id: $deprecated_id})
            SET e.merged_into = $surviving_id,
                e.merged_at   = datetime()
        """, deprecated_id=deprecated_id, surviving_id=surviving_id)

    return outgoing + incoming