Brummel
7f3756a395
Cycle 2 of the "Cost-model graph (in R)" milestone (#148): the milestone's real architectural claim — the cost graph composes. Two cost nodes now sum into one net-R curve while summarize_r and the net_r_equity tap stay structurally unchanged. - VolSlippageCost (aura-std): a second, STATE-DEPENDENT cost node; per-trade charge = slip_vol_mult * volatility / |entry-stop|, in R. The vol is an independent short-horizon realized range (SLIP_VOL_LENGTH=5, distinct from the stop's EWMA-3) — scaling slippage by the stop's own vol would collapse cost-in-R to a constant (indistinguishable from ConstantCost). - CostSum (aura-std): the cost-graph OUTPUT node — sums N cost nodes' 3-field cost-in-R records per-field into one aggregate. summarize_r and net_r_equity read the aggregate (one home for cost; n=1 is the identity, so the cost path is uniform). A future CostNode trait (deferred) will unify the cost-triple the two producer nodes currently restate by-convention. - Run path: --cost-per-trade and --slip-vol-mult combine, their costs summing into the net-R curve; a hoisted vol proxy (RollingMax-RollingMin) keeps the single feed. Run-path-scoped; sweep/walkforward/mc pass None. Co-temporality contract (the load-bearing design decision; corrected from the signed spec after the implement-loop correctly BLOCKED Task 3 on it). summarize_r positional-joins cost[i] <-> record[i], so the cost stream must be co-temporal 1:1 with the PM record. A cost node is therefore gated ONLY by the PM geometry (closed/open/entry/stop); a not-yet-warm state input (the vol proxy warms later than PM) contributes 0 cost that cycle rather than withholding and desyncing the stream. This makes co-temporality structural + warmup-independent, preserves the C18 golden, and generalizes to any future cost factor. The rejected alternative (a key-join in summarize_r) would have moved the golden and pushed cost-graph logic into the post-run fold. Recorded on #148. Tests: VolSlippageCost + CostSum unit sets (incl. the co-temporal-zero-during- warmup case); the CLI composition run (both flags -> net_both < net_flat, net_r_equity persisted); node-level EXACT additive composition (net_both == net_flat + net_vol - gross over the real nodes), the aggregate net_r_equity == post-run net total, and CostSum(1) identity. Full workspace suite green; clippy -D warnings clean; the no-cost C18 golden byte-identical (the regression floor). Deferred (later cycles of this milestone): the general CostNode trait + cost-graph composite-builder (now justified by two concrete nodes), the conviction-weighting R-aggregation axis, and cost on the reduce-mode sweep path. Spec + plan amended to the corrected contract; both are cycle ephemera (git rm at cycle close). refs #148