feat(adr-0181-p5): audio Delta-CRDT arena + merge kernel (sequential==concurrent proof) (#477)
Wires AudioCompilationUnits into the Delta-CRDT substrate (ADR-0180 §2.1/§2.2)
at the Python layer — audio is the first concrete exerciser of ADR-0180.
- sensorium/audio/arena.py:
- AudioArena (§2.1): thread-local, share-nothing, lock-free accumulation;
non-destructive snapshot(); thread_local_audio_arena() accessor.
- AudioDelta (§2.2): canonical, content-addressed merge_key order + dedup;
join is commutative/associative/idempotent.
- merge_audio_deltas (§2.2): the Merge Kernel — folds arena deltas into one
content-addressed, deduped, totally ordered set.
- audio_merge_trace_hash: PCM-free, order-invariant trace hash — the
sequential==concurrent proof anchor (ADR-0181 §4.2 A-3/A-6).
Mirrors the Rust LocalArena/SemilatticeDelta/merge_kernel (core-rs/src/vault.rs,
ADR-0180 §4.1) so the layers stay in parity when the Rust↔Python binding lands
(§1.5.5, deferred — pure-CPU/Python path first).
10 failable proof tests in tests/test_audio_crdt_merge.py covering the
load-bearing hash(Sequential)==hash(Concurrent) gate (real threads), the three
semilattice legs, content-addressed ordering, dedup idempotence, and trace
hygiene. Mutation-verified: disabling the content sort fails 6 of 10 loudly.
Additive only: no core layer touched (ADR-0013). Audio tests 35/35; architectural
invariants 40/40. Zero impact on existing eval lanes (no serving path changed).
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