Function decode_frame 

pub fn decode_frame(
    buf: &[u8],
    max_frame_bytes: usize,
) -> Result<Frame, CodecError>

Decode one complete length-prefixed frame from buf against an explicit max_frame_bytes bound. See FrameCodec::decode for the contract.

max_frame_bytes is PAYLOAD-ONLY: the maximum JSON payload length, not counting the 4-byte prefix. Passing a total wire length here is a caller bug — it admits payloads 4 bytes over the intended bound.