pub const DECODE_DOMAIN: u64 = 0xD3C0_DE12_A5B6_C7D8;Expand description
2026-09-25: Domain separator mixed with the model fingerprint to form the
SSM decode-ring cold-tier namespace (derive_decode_ns_salted in
metrale-model-engine), which keeps decode keys apart from other key
spaces derived from the same fingerprint.