feat(research,cli): the CostSpec campaign vocabulary (#234 task 2)
CampaignDoc gains an additive cost: Vec<CostSpec> block — a closed,
externally tagged vocabulary over the three shipped cost nodes
(constant/vol_slippage/carry, field names = the builders' ParamSpec
names), mirroring the risk block: serde default + skip-if-empty (cost-
less documents keep their content ids, pinned), DocFault::BadCost
validation (finite/bounds per component), std::cost construct-
vocabulary block + SlotKind::Costs + open-slot mirror, prose arm, and
all CampaignDoc struct literals across crates carry cost: vec![]
(compile-driven).
Verified: aura-research suite green, campaign validate e2e green, full
workspace suite green, clippy -D warnings clean; in-loop spec review
compliant and quality review approved (real diff fingerprint — the
worktree-anchored review prompt works).
refs #234
Brummel
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