Constant DISCOVER_PGVECTOR_COLUMNS_QUERY 

const DISCOVER_PGVECTOR_COLUMNS_QUERY: &str = r#"
    SELECT
      a.attname as column_name,
      a.atttypmod as atttypmod,
      format_type(a.atttypid, a.atttypmod) as formatted_type
    FROM pg_attribute a
    JOIN pg_class c ON c.oid = a.attrelid
    JOIN pg_namespace n ON n.oid = c.relnamespace
    JOIN pg_type t ON t.oid = a.atttypid
    WHERE n.nspname = $1
      AND c.relname = $2
      AND t.typname = 'vector'
      AND a.attnum > 0
      AND NOT a.attisdropped
    ORDER BY a.attnum
"#;

Discover pgvector columns with both atttypmod (dimension) and format_type text. vector(n) is stored as atttypmod = n, while dimension-less vector uses -1. We rely on this to keep user-defined type modifiers that are not preserved by sea-schema.