Function record_version 

pub fn record_version(
    fs: &impl Fs,
    paths: &StorePaths,
    clock: &impl Clock,
    doc_id: &str,
    content: &[u8],
    meta: VersionMeta<'_>,
) -> Result<VersionOutcome, SessionError>

Record content as a new durable version. meta.label names it (a named version is retained forever by the retention pass). meta.op_kind is an optional category label. UNNAMED (auto) versions deduplicate against the LATEST version: if content is byte-identical to it, the call returns Unchanged and appends nothing. A NAMED version (meta.label.is_some()) is an explicit checkpoint and is ALWAYS recorded, even when its content matches the latest version.