audit(0081): cycle close — drift-clean (code); ledger C10 realization note + stale-broker doc sync (refs #148)

Cycle 0081 (cost-model graph, cycle 1) closes drift-clean against C10: the
architect review confirmed ConstantCost + the net-R seam realize the contract
at its floor (C9 cost node; net_r_equity a C8/C18 sink; R-pure; one home for
cost, subsuming the retired scalar round_trip_cost; pure feed-forward C1), and
the no-cost baseline is byte-identical (C18 golden held). Regression gate green
and unchanged: full workspace suite 0-fail, clippy --workspace --all-targets
-D warnings clean. No baseline moved -> no ratify.

Ledger sync (docs/design/INDEX.md): added the C10 cycle-0081 realization note
(ConstantCost node + net_r_equity seam shipped; scalar round_trip_cost retired;
run-path-scoped; later-cycle deferrals named).

Drift swept (cycle-adjacent + cheap one-liners):
- crates/aura-analysis/src/lib.rs net_expectancy_r doc: the removed in-fold
  mechanic (mean(R - round_trip_cost/latched_dist)) -> the cost-stream fold.
- crates/aura-std/src/lib.rs module doc: "realistic broker profiles" (retired
  by #116) -> the legacy SimBroker pip yardstick + cost-model nodes.

Backlogged (pre-existing, broader, predates this cycle): the
docs/project-layout.md backtest worked example is stale on #117 (exposure->bias)
and #116 (realistic broker); a proper rewrite is filed as #151, not folded here.

Architect-accepted: the #[allow(dead_code)] on r_col::ENTRY_PRICE/STOP_PRICE
(their production reader legitimately removed when summarize_r stopped recovering
latched_dist; still the layout contract + exercised by test fixtures).

Spec + plan ephemera removed (git rm docs/specs/0081, docs/plans/0081).

refs #148

docs/design/INDEX.md

@@ -714,6 +714,25 @@ yardstick, not to be expanded. (Terminology note: with Stage 2 gone, the
 only as a historical cycle / identifier name, like the `exposure` → `bias` on-disk
 alias, denoting the shipped feed-forward R chain.)
 
+**Realization (cycle 0081 — cost-model graph, cycle 1, #148).** The first concrete
+cost node + the net-R seam shipped. `ConstantCost` (`aura-std`) is an ordinary
+downstream node (C9) emitting a 3-field cost-in-R record `{cost_in_r, cum_cost_in_r,
+open_cost_in_r}` isomorphic to `PositionManagement`'s R-triple; R-pure
+(`cost_per_trade / |entry − stop|`, notional cancels, no equity held). The scalar
+`round_trip_cost` argument of `summarize_r` is **retired**: `summarize_r` folds a
+co-temporal cost stream (positional 1:1 join — `cost[i]` is `record[i]`'s cycle) into
+`net_expectancy_r`, one home for cost / no double-count, byte-identical to the old
+cost = 0 baseline on an empty stream. The headline sink is **`net_r_equity`** =
+`LinComb(4)[cum_realized_r, unrealized_r, −cum_cost_in_r, −open_cost_in_r]` → Recorder
+(C8/C18), a sibling of `r_equity`, emitted only when a cost is authored. Wired on the
+**run path** via `--cost-per-trade` (`stage1_r_graph`); sweep / walk-forward / mc pass
+`None` (cost on the reduce-mode sweep path and cost in OOS pooling deferred — the
+positional join holds only while one cost node fires in lockstep with PM). Deferred to
+later milestone cycles: the general `CostNode` trait + multi-node cost-graph
+composite-builder, data-grounded factors (realized-vol → slippage, recorded-rate →
+swap), per-cycle-held accrual (carry / funding), and the conviction-weighting
+R-aggregation axis. Decision log: #148.
+
 **Reframe (2026-06-23, #117 — exposure → bias, R as the signal-quality unit).**
 [HISTORY — its R spine survives into the 2026-06-28 contract; its Stage-2 currency /
 realistic-broker / register / flat-1R-vs-compounding portions are SUPERSEDED by that