Deterministic EcBitrotProtection -> exact on-disk bytes, asserted against a
canonical constant on BOTH sides (this test and ec_bitrot.rs), so a format drift
in either binary fails its own suite rather than silently desyncing a Go-written
.ecsum from a Rust-written one.
Claude-Session: https://claude.ai/code/session_015EE9Sc9EvNp8BCVva4RKdo