v0.18.0 — the replication release

The HA seams get the consumer that would have noticed if they were phantoms, and the edge stops holding plaintext.

• EngineSnapshot.Digest — the crash-recovery fingerprint, promoted from a test helper to a contract.
• wal.SetOnAppend — the live log tail. Its first shape handed subscribers a pointer into state the matcher keeps mutating; the drills' first -race run caught it, and the hook now hands record bytes — the wire is byte-identical to the log.
• examples/replication — the drilled primary-backup reference: async shipping with a measured loss window, the incarnation fence on promotion, drills D1–D6 in CI, and a failover runbook. Split-brain prevention stays deliberately yours.
• Digests at rest — orderentry.HashedAccounts, sha256: credential entries, and obgw -hash-secret. A memory disclosure now yields digests, not passwords; rotation, revocation and expiry remain honestly absent.

Full detail: CHANGELOG.md, docs/REPLICATION.md — including §8, what building it found versus what the spec predicted.