Function decode_frame 

pub fn decode_frame(
    raw: Option<&[u8]>,
    tracked: bool,
    watermark: Option<&[u8]>,
) -> Result<ReadResult, ProtocolError>

Classify one raw read with the protocol’s precedence: absent value, unsupported frame, tracked marker validity and zero stamp, fence, payload encoding, then a hit.

watermark is consulted only when tracked. A miss carries the parsed fence whenever the marker was valid (including the absent baseline, which carries none); a malformed marker yields an unclassified miss without one. The stamp is returned with full u64 precision; the safe-integer check belongs to normalize_read_result.