The optimizer is choosing a generic query plan over a custom plan when the custom plan has bounded…

The optimizer is choosing a generic query plan over a custom plan when the custom plan has bounded…: a task in LegoFlow-SWE (Harbor dataset). PREPARE p AS SELECT FROM ( SELECT id FROM t WHERE a = $1 AND b = $2 ORDER BY b, id LIMIT 250 ) UNION SELECT FROM ( SELECT id FROM t WHERE a = $3 AND b = $4 );