Implements ADR-0180 §4.1 item 1: the Delta-CRDT write-accumulation substrate
in core-rs/src/vault.rs.
- ArenaEntry: (versor, provenance) — provenance is part of the content key.
- LocalArena (§2.1): thread-local, share-nothing, lock-free write cache;
snapshot() emits a canonical Delta; non-destructive (flush/GC is the kernel's
concern, safe across the §3.2 eventual-consistency window).
- SemilatticeDelta trait + Delta (§2.2): join is commutative, associative,
idempotent under content-addressed equality (IEEE-754 versor bits +
provenance bytes), never arrival order — per the §2.2 amendment landed today.
- merge_kernel (§2.2): folds deltas into one content-addressed, deduped,
totally ordered set; permutation- and duplicate-invariant — the property
§4.3's hash(Sequential)==hash(Concurrent) rides on.
Pure-CPU only (§1.5.5): no MLX/UMA handshake, no Python binding — those are
downstream (§4.1 item 2; ADR-0181 PR-5). Existing vault recall/reproject paths
untouched; zero eval impact.
10 failable property tests in tests/test_arena.rs (mutation-verified: disabling
the content sort fails 6 of them loudly, per CLAUDE.md §Schema-Defined Proof
Obligations). Also fixes a pre-existing broken doctest in the vault.rs header
(indented math block was parsed as a Rust doctest).
