audit: cycle 0007 tidy — add C10 Realization (cycle 0007) note

Architect drift review (f000373..HEAD) found one item: the C10 reframe was
amended in framing but carried no "Realization (cycle 0007)" note recording what
actually shipped — the spec's own ship gate required it (C8/C22 carry their
realization notes; C10 did not). Added: the signal-quality half realized as
Exposure { scale } + SimBroker { pip_size } on the unchanged, domain-free engine,
with the position-management half explicitly confirmed deferred.

Everything else holds: the reframe is propagated consistently across CLAUDE.md
invariant #7, the seven touched glossary entries + the new exposure-stream entry,
and project-layout.md (no stale "position table is the strategy output"
survivor); the engine stays domain-free (the only RefCell hit in aura-engine/src
is a #[cfg(test)] doc comment); C1 determinism and C2 causality are each pinned by
a behaviour test asserting observable output, not internals.

No regression scripts configured (commands.regression empty) — that gate is a
no-op; architect is the gate. Cycle 0007 is drift-clean.

refs #4 #5

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

docs/design/INDEX.md

@@ -311,6 +311,22 @@ broker nodes then test real-world viability. Modelling brokers as nodes (not a
 bespoke subsystem) keeps them within the one Node/graph abstraction (C9). This
 supersedes the earlier "the strategy's output is the position-event table"
 framing (cycle 0007 reframe).
+**Realization (cycle 0007).** The signal-quality half of this contract is now
+realized at the substrate, as two `aura-std` nodes composed on the unchanged
+engine (the engine stays domain-free — it routes only `f64` records, never
+"exposure" or "equity"). The **exposure stream** is realized as `Exposure { scale
+}`: the decision/sizing node, `clamp(signal / scale, -1, +1)`, one `f64` per fired
+cycle (`None` until warmed up). The **sim-optimal broker** is realized as
+`SimBroker { pip_size }`: a two-input node (exposure, price) that accumulates
+`prev_exposure · (price − prev_price) / pip_size` and emits cumulative pip equity
+— the exposure held *into* a cycle (decided at t-1) earns that cycle's return, so
+the integration is causal (C2), and `pip_size` is held reference metadata
+(C7/C15), never streamed. An end-to-end harness (SMA-cross → `Exposure` →
+`SimBroker` → recording sink) produces a recorded pip-equity curve, bit-identical
+across runs (C1). The **position-management half** — deriving the position-event
+table (buy/sell/close, `position_id`, partial closes) from the exposure history,
+and the realistic broker nodes that consume it — is deliberately **not** built
+this cycle; it remains the decoupled, derived, deferred layer described above.
 
 ### C11 — Generalized sources; record-then-replay determinism boundary
 **Guarantee.** A source is anything that produces timestamped scalar streams —