Function list_entity_names_by_relation 

pub fn list_entity_names_by_relation(
    conn: &Connection,
    namespace: &str,
    relation: &str,
) -> Result<Vec<String>, AppError>

Returns unique entity names involved in relationships of the given type.

Queries both source and target sides of every matching relationship row, deduplicates via DISTINCT, and returns the names in alphabetical order.

Errors

Returns Err(AppError::Database) on any rusqlite failure.