Function read_frame 

pub async fn read_frame<R, T>(reader: &mut R) -> Result<Option<T>, CodecError>
where
    R: AsyncRead + Unpin,
    T: DeserializeOwned,

Reads one length-prefixed task protocol message.

A clean end of stream before the next frame returns Ok(None).

Errors

Returns an error when the transport fails mid-frame, the declared frame is oversized, or the payload cannot be decoded.