pub fn validate_presence_byte(byte: u8) -> Result<(), Error>Expand description
Validate a presence_byte from a WalletPolicyId canonical-record
preimage (spec v0.13 §5.3). Bit 0 = fp_present, bit 1 =
xpub_present, bits 2..7 reserved (must be 0). Returns
Error::InvalidPresenceByte with the offending reserved-bit
field if any of bits 2..7 is set.
v0.13’s encoder masks reserved bits when building the preimage, so
this helper is unreachable on v0.13 wire today. It enforces the
spec §5.3 “decoders MUST reject” clause for any future
canonical-record consumer (e.g., a verification-mode tool that
reconstructs the preimage to cross-check a WalletPolicyId).