GET /feeds/similar-markets/outcome-stats

Outcome aggregation — the core B2B semantic search product. Given a market question (text) or instance ID, finds comparable resolved markets and returns their outcome distribution (for example, '62% Up, 38% Down across 50 similar markets'). Domain isolation is automatic, and coin plus market kind are inferred when omitted, preventing incompatible outcomes from financial, aviation, environment or other domains from being mixed. Includes sample sufficiency, similarity threshold, per-coin breakdown and top matches. Supports explicit ?domain, ?coin and ?kind filters.