Function observe_version 

pub fn observe_version(
    dir: &Path,
    agent_key: &str,
    provider: &str,
    version: &str,
) -> Option<String>

Record that agent_key’s CLI just started on version, and return the version it last ran if that was a different one of the same provider. A first run, or a switch to another provider, records and returns None. A record that can’t be read or written is logged and treated as empty: at worst a notice is missed, never a launch.