Atomically replaces one private state file and syncs both its bytes and directory entry. A failure before the rename
(a value JSON cannot hold, a full disk, a rename refused) removes the temporary file it made and throws that error,
so no copy of the state is left beside the file.
Atomically replaces one private state file and syncs both its bytes and directory entry. A failure before the rename (a value JSON cannot hold, a full disk, a rename refused) removes the temporary file it made and throws that error, so no copy of the state is left beside the file.