canonicalDigest

A 64-bit digest of value's canonical CBOR encoding — FNV-1a.

Two replicas that have converged share a digest; two that have diverged almost certainly do not. Intended for the cases where comparing the states directly is impossible:

• cross-process and real-socket tests, where shipping one Long back for assertion beats shipping a whole state;

• a divergence alarm between live peers, in a harness or test rig.

Test- and harness-side only: :kuilt-conformance api-exposes kotlin-test, so it does not belong on a production classpath.

In-process, assertEquals(a, b) is strictly better — exact, no collision risk, and a far better failure message. The convergence harness deliberately compares raw bytes rather than digests for that reason; this exists only for the boundary-crossing cases.

Correctness rests on the encoding being canonical — a digest over a non-canonical encoding reports permanent false divergence. Within one target that is enforced by the byte assertion in LatticeLawHarness (every merge order must encode identically) and, per CRDT type, by CanonicalSerializationTest in :kuilt-crdt's commonTest (issue #1957).

The cross-target dimension is pinned as well, by CanonicalGoldenVectorTest in the same source set. It holds checked-in CBOR byte strings for ten zoo types, covering every Canonical*Serializer site plus DotMapSerializer, and commonTest compiles and runs on JVM, Android, iOS, macOS and wasmJs, so every target is held to the same constants — which is what the cross-process use above needs. For those ten, a digest mismatch between peers on different targets reads as real divergence rather than as an artefact of the encoding. Types outside them — MVRegister, ResettableCounter, Rga, Fugue, JsonCrdt — have no cross-target byte pin; see that file's KDoc.

The caveat there is latency, not coverage: ci-required's build jobs run on Linux, so per-PR only the JVM/Android and wasmJs executions happen — the Apple Kotlin/Native ones live in apple-nightly.yml, which is not a required check. JVM-vs-wasm agreement is gated on every PR, JVM-vs-Apple agreement nightly.

Not cryptographic — do not use it to authenticate state. It is a 64-bit non-keyed hash: fine against accidental divergence, no defence against a peer that forges a matching digest.