Function backup_pager_to_path 

pub fn backup_pager_to_path<F: FileBackend>(
    source: &Pager<F>,
    snapshot: &ReaderSnapshot<F>,
    dest: impl AsRef<Path>,
) -> Result<()>

Build a self-contained .obj file at dest carrying the state of source as of snapshot.pinned_lsn().

snapshot MUST have been taken against source and not yet dropped; the pin keeps the source’s WAL frames at-or-below the pinned LSN from being reclaimed while the backup runs.

Algorithm

1. Refuse to overwrite an existing dest (create_new).
2. Copy main-file pages 0..source.page_count() byte-for-byte.
3. Overlay every frame in the snapshot’s frozen WAL view onto the destination at its page-id offset.
4. If the snapshot’s frozen view carries a page-0 header frame, overlay that on top of the main-file copy of page 0.
5. Patch the destination header: zero wal_salt, recompute the header CRC32C.
6. sync_data(SyncMode::Full) on the destination.

On any mid-backup error the destination file is removed best- effort so a half-written backup does not linger.

Errors

• Error::BackupDestinationExists if dest already exists.
• Error::BackupNotSupportedForMemoryPager if source is an in-memory pager.
• Error::Io on any syscall failure during the copy.
• Error::InvalidFormat / Error::Corruption propagated from the source header decode (the source’s header bytes are re-encoded with the WAL-staged values applied).