Yeah. SQLite's backup API is the right way to do this:

https://sqlite.org/backup.html

And, if you can't use the backup API for some reason, try VACUUM INTO:

https://www.sqlite.org/lang_vacuum.html#vacuum_with_an_into_...

Would creating a ZFS snapshot, then either copying from that snapshot or sending it to another machine with zfs send, also be reliable? IIUC, ZFS snapshots are point-in-time consistent.

Beat me to mentioning this. Rsync is not a safe database backup tool. Period. It can be used to move around backups created by whatever specific database tool generated them, but just blindly using rsync is a recipe for unrecoverable corruption