Brummel
9fb3d8b8ee
Cycle 4 of milestone #148 (Cost-model graph in R), decision E — the cost-graph composite-builder, recorded across cycles 2-3 as the natural next. Adds a `cost_graph(Vec<PrimitiveBuilder>) -> Composite` builder in aura-composites that fans the 4 PM-geometry inputs to N cost nodes, surfaces each node's extra inputs as `cost[k].<port>` roles (schema introspection past GEOMETRY_WIDTH), sums them via 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. Re-exports GEOMETRY_WIDTH from aura-std (first cross-crate consumer). Behaviour-preserving at the value level: the composite inlines at bootstrap (C11) to the same flat computation, so the two cycle-3 net_expectancy_r goldens, the C18 no-cost golden, and the full suite stay green verbatim. Routed spec-driven (specify direct-entry): settled in #148's scope + the mature aura-composites idiom + the CostNode contract. All four forks (composite API shape, extra-input namespacing, GEOMETRY_WIDTH visibility, CLI consumption) are derived decisions logged on #148; none hangs on pure user preference. Auto-signed under /boss on the Step-5 grounding-check PASS (every load-bearing current-behaviour assumption tied to a named green test or current source; no with-cost graph label/shape pin contradicts the C23-permitted label drift). refs #148