Brummel
d5c44dd1ea
Cycle 4 of milestone #148 (Cost-model graph in R), decision E. New `cost_graph(Vec<PrimitiveBuilder>) -> Composite` in aura-composites: it fans the 4 PM-geometry inputs to N cost nodes, surfaces each node's extra inputs (discovered via schema introspection past GEOMETRY_WIDTH) as `cost[k].<port>` roles, sums them through CostSum, and exposes the 3-field aggregate. Replaces the CLI's manual slot-indexed cost-wiring + the hardcoded MAX_RUN_COST_NODES=2 cap with one principled composite of arbitrary arity. GEOMETRY_WIDTH re-exported from aura-std (first cross-crate consumer). Runtime port names .leak()'d (the risk_executor precedent), a bounded one-time cost at blueprint construction. Behaviour-preserving at the value level: the composite inlines at bootstrap (C11) to the same flat fan-in, so the two cycle-3 net_expectancy_r goldens (-614.3134020253314 flat, -615.0304388396047 composed), the C18 no-cost golden, and the full suite stay green verbatim. Honours C9 (a composite of cost nodes is ordinary downstream nodes), C16 (wiring lives in aura-composites, not aura-engine), C23 (label drift under cost_graph nesting is permitted; no with-cost graph label/shape golden exists). Four aura-composites unit tests pin the exposed contract: the two planned (n=2 heterogeneous role set; n=1 no-extra shape) plus two the implementer added that strengthen the headline — arbitrary-arity per-node namespacing (n=3, two VolSlippageCost -> distinct cost[1]/cost[2].volatility, the property that retires the 2-node cap) and geometry fan-once (n=2 extra-free -> only the 4 geometry roles). Accepted nit (held, non-gating): the CLI reconstructs the `cost[k].volatility` role name to feed the vol node's extra input — a string coupling to the composite's public role-naming convention. Kept: role-based composite wiring addresses roles by name (as the CLI already does for "closed"/"bias"/"price"); the convention is tested + build-validated; a decoupling accessor would widen this cycle's scope. Verified: cargo test --workspace (0 failures), clippy --workspace --all-targets -D warnings clean, cargo doc -p aura-composites clean. refs #148