impl(sprint-11/wave-D): D-CSV-7 MailboxSoA + D-CSV-6a WitnessCorpus core (parallel workers)

Wave D Phase B substrate primitives, two parallel Sonnet workers:

D-CSV-7 (W-D1) — MailboxSoA<N> core in cognitive-shader-driver
- NEW `crates/cognitive-shader-driver/src/mailbox_soa.rs` (~431 LOC,
  source + 9 tests).
- `pub struct MailboxSoA<const N: usize>` with `mailbox_id`, per-row
  `energy: [f32; N]`, `plasticity_counter: [u8; N]`,
  `last_emission_cycle: [u32; N]`, `current_cycle: u32`, `w_slot: u8`
  (panics if ≥ 64 per L-6), `threshold: f32`.
- `apply_edges(batons)` — baton receipt with W-slot filter (mismatched
  edges silently dropped); energy accumulated as
  `mantissa/8.0 × confidence`; plasticity_counter saturating-add.
- `emit(source) -> CollapseGateEmission` — single-shot per cycle
  (`last_emission_cycle` guard); above-threshold rows produce batons
  with `with_inference_mantissa(...)` + `with_w_slot(self.w_slot)`;
  emitted rows reset to 0.
- `tick()` advances cycle; `reset_row(row)` clears one row;
  `pending_count()`, `energy_at`, `plasticity_at`, `cycle`, `w_slot`
  inspectors.
- `pub type DefaultMailboxSoA = MailboxSoA<1024>;`
- 9 tests cover: zeros init, w_slot panic >63, accumulation,
  wrong-w-slot reject, out-of-range target reject, emit-above-thresh,
  emit-below-thresh-no-baton, double-emit-same-cycle-idempotent,
  tick-then-re-emit.

D-CSV-6a (W-D2) — WitnessCorpus core in lance-graph arigraph
- NEW `crates/lance-graph/src/graph/arigraph/witness_corpus.rs`
  (~398 LOC, source + 8 tests).
- `pub struct WitnessEntry { spo: u64, timestamp_ns: u64,
  source_url: Option<String>, evidence_blob: Bytes }` with
  `tie_break_hash()` (DefaultHasher of source_url; None → 0) and
  `ord_key() = (timestamp_ns, tie_break_hash)`.
- `pub struct WitnessId(pub u64)` — opaque handle from ord_key.
- `pub struct CamPqIndexPlaceholder` — empty unit; D-CSV-6b replaces
  with real ndarray CAM-PQ codec wiring. Out of scope here.
- `pub struct WitnessCorpus { entries: Arc<Vec<WitnessEntry>>,
  cam_pq_index: CamPqIndexPlaceholder }` — copy-on-write via
  `Arc::make_mut`.
- `insert(entry) -> WitnessId` — binary-search position to maintain
  W5-INV-CHAIN-ORDER (timestamp_ns ASC + hash tie-break).
- `query(spo) -> impl Iterator` — linear scan by SPO match; returns
  in chain order. D-CSV-6b will swap for CAM-PQ-backed lookup.
- `iter()`, `len()`, `is_empty()`, `evict_stale_before(cutoff_ns)`
  (returns count of evicted entries).
- 8 tests cover: empty init, ord_key correctness (None hash 0,
  same source_url → same hash), insert chain-order with reverse
  insertion, tie-break ordering, query SPO filter, unbounded
  100-entry insert (W5-INV-WITNESS-UNBOUNDED), evict_stale_before
  threshold semantics, Arc CoW (clone shares; mutate splits).

Out of scope (D-CSV-6b in follow-up PR)
- Real CAM-PQ index integration (ndarray hot-path wiring)
- `cam_pq_search` method (linear-scan `query()` is the placeholder)
- Benches
- WitnessCorpusStore (the 64-slot W-slot keyed array)

Out of scope (D-CSV-7 follow-ups)
- AttentionMask SoA / AttentionMaskActor (W6 spec §2-§3 — orthogonal)
- Ractor actor wrapping (sprint-12 Σ-tier dispatch in D-CSV-10)
- LRU eviction (sprint-12+)
- Cross-cycle plasticity rollup (Zone 2; outside MailboxSoA scope per
  W6 §4.4)

Cargo.toml: `crates/lance-graph` adds `bytes = "1"` (used by
WitnessEntry.evidence_blob). Cargo.lock files updated.

Validation note
The W-D1 + W-D2 workers may still be polishing; this commit captures
the current file state. If workers write additional refinements after
this commit, those land in a follow-up commit on the same branch.
Both workers report completion notifications fire when their cargo
test step finishes; main thread will validate via CI.

https://claude.ai/code/session_01UwJuKqP828qyX1VkLgGJFS

Author: claude