Function grant_durable 

fn grant_durable(
    conn: &mut Smb2Conn,
    req: &CreateReq,
    fid: [u8; 16],
    rel: &str,
    is_dir: bool,
    lease_state: Option<u32>,
    is_ca: bool,
) -> Option<(&'static [u8], Vec<u8>)>

Record a durable-handle grant on the connection and return the response create-context to echo. Directories and one-shot deletes are ineligible. A durable open also requires a batch oplock or a handle-caching lease, so lease_state (the granted lease bits, if any) gates the grant; persistence is only granted on a continuous-availability share (is_ca).