Function read_version_text 

pub fn read_version_text(
    directory: &Path,
    identity: &BinaryIdentity,
) -> Option<Vec<u8>>

What: The git version text recorded for exactly this identity, or None for a missing, foreign, unreadable or stale entry. Why: Anything but an exact match of the whole identity line is stale, and the caller then asks Git.

In TS you’d write (pseudocode):

const file = await readFile(cacheFile(dir, identity)); return file.startsWith(TAG + identity.text + '\n') ? file.slice(...) : undefined;