sqlite: backup() never settles when rate is 0

[trivikr]

Version

main

Platform

N/A

Subsystem

sqlite

What steps will reproduce the bug?

import { backup, DatabaseSync } from 'node:sqlite';
import { setTimeout } from 'node:timers/promises';

const source = new DatabaseSync(':memory:');
source.exec(`
 CREATE TABLE data (value TEXT);
 INSERT INTO data VALUES ('example');
`);

const outcome = await Promise.race([
 backup(source, 'backup.db', { rate: 0 }),
 setTimeout(1_000, 'backup still pending after 1 second'),
]);

console.log(outcome);
process.exit();

How often does it reproduce? Is there a required condition?

Always

What is the expected behavior? Why is that the expected behavior?

zero should be rejected as an invalid rate, or explicitly treated as a documented single-call mode.

What do you see instead?

backup still pending after 1 second

backup() accepts rate: 0 and its promise remains pending indefinitely while zero-page jobs are repeatedly scheduled.

Additional information

No response

[trivikr]

Fix is posted at #64893