Function decode 

pub fn decode(
    input: &[u8],
    receiver: ReceiverDirection,
) -> Result<ParticipantFrame, CodecError>

Decodes one exact complete participant frame for receiver.

Counts are proven against the already bounded remaining frame before any list allocation. Extra bytes inside or outside the declared complete frame are rejected as non-canonical by this exact-frame API.

Errors

Returns CodecError::NotParticipantFrame before participant framing when the generic outer type differs, the contract’s canonical structural class, or CodecError::UnsupportedVersion before discriminant/body decoding.