Task-by-task plan for spec 0082: the VolSlippageCost node (Task 1) and the
CostSum aggregator (Task 2) in aura-std; the run-path wiring as one compile-gate
task (Task 3) — stage1_r_graph cost-param widening + vol-proxy hoist + the
CostSum-aggregated cost block + the --slip-vol-mult thread-through across all
call sites, with a CLI composition test and the no-cost golden floor; and the
node-level exact-sum composition tests (Task 4). RED-first per task. The
&'static str CostSum port names are interned (COST_SUM_PORTS, mirroring
COL_PORTS); summarize_r is unchanged (it folds the CostSum aggregate).
refs #148
Brummel
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