Get all sibling outcomes for the event containing a market

Returns every outcome in the event that market_id belongs to (for multi-outcome / grouped markets), served from a cache of pre-computed event/market lookups. Any identifier (market_id, token_id, condition_id, symbol, slug) is mapped to its event_id; if that misses, falls back to the per-market entry's embedded event_id, then to deriving a Kalshi-style event ticker by stripping the last -SEGMENT off market_id (e.g. KXPGATOUR-THGI26-SSTR → KXPGATOUR-THGI26). If no event can be resolved at all and provider=polymarket, falls back to a live Polymarket lookup — guarding against a known upstream quirk that can silently return an unrelated default result instead of an empty list. Non-Polymarket providers get no such fallback — an unresolvable event returns the empty shape. all_ids (comma-separated, ≤200 ids, each ≤128 chars) additionally resolves event_groups — a map from every supplied id (and every sibling id discovered while resolving events) to its event_id, used by the frontend to dedupe sibling contracts across dropdowns. Price scale note: unlike most of this API, outcome prices here are returned as a 0–1 decimal probability, not the platform's usual 0–100 cents scale.