env “TMPDIR" can't change the tmp store diretory

[runlilong]

my codes

package main

import (
	"database/sql"
	"log"
	"os"

	_ "github.com/mattn/go-sqlite3"
)

func main() {
	os.Setenv("TMPDIR", "/mnt/test")
	db, err := sql.Open("sqlite3", "db.bak")
	if err != nil {
		log.Fatal(err)
	}
	defer db.Close()

	_, err = db.Exec("VACUUM")
	if err != nil {
		log.Fatal("Failed to vacuum database:", err)
	} else {
		log.Println("Database vacuumed successfully")
	}
}

❯ du -d1 -h db.bak
84M     db.bak

❯ df -h
/dev/loop0              1003K  931K  1.0K 100% /mnt/test

the result of it

azTempDirs[0] = NULL
azTempDirs[1] = /mnt/test
2024/02/21 20:40:06 Database vacuumed successfully

while sqlite3 report the error

❯ export TMPDIR=/mnt/test
❯ sqlite3 db.bak -cmd "VACUUM" .quit

Error: database or disk is full

which says sqlite3 cli used the specified TMPDIR but the code didn't.