Function try_decode_session_frame 

pub fn try_decode_session_frame(
    buf: &[u8],
) -> Result<Option<DecodedSessionFrame>, SessionCodecError>

Incrementally decode one SESSION-lane SessionFrame from the front of buf.

Returns Ok(None) when buf does not yet hold a complete frame — the caller reads more bytes and retries. On Ok(Some(decoded)) the caller consumes decoded.consumed bytes. This mirrors try_decode_framed and adds the SESSION-lane payload decode on top.

Errors

• SessionCodecError::Framing for a malformed outer frame (bad framing version, oversize, or undecodable envelope).
• SessionCodecError::WrongProtocol when the envelope is well-formed but is not on the SESSION lane — a caller multiplexing lanes must route by payload_protocol before calling this.
• SessionCodecError::Decode when the envelope payload is not a valid SessionFrame.