Function lock_session 

pub fn lock_session(
    id: &str,
    continued: bool,
    kind: &str,
) -> Result<Option<SessionLock>, RuntimeError>

The session lock for a boot() host that drives Runtime itself (rpc, synaps server). Continuing a session that another process (a TUI, the daemon, another rpc) holds is REFUSED: two writers would fork its history and the older one’s saves would overwrite the newer’s. So is continuing a session already compacted into a successor (its history is closed). A fresh session, or a lock that cannot be taken for another reason (e.g. a read-only sessions dir), proceeds best-effort, as the session actor does. The lock is held for the returned value’s lifetime; a holder that continued a session runs crash recovery (recover_turn_draft).