Corpus-wide place search (CORPUS_SEARCH_DESIGN.md §4.2). lat/lng bias to a ~50km box with auto-widen.

mode defaults to the shipping product one: hybrid, so a client that sends q/limit/sid only (all of them do) gets the BM25 + ANN fusion. It is ungated — the admin preview's eval toggle picks bm25/semantic, and neither costs more embedding budget than the default already spends.

preview stays admin-only — it marks a serve as excluded from training data, so honouring it from arbitrary callers would let real user searches opt themselves out. Coerced rather than 400'd: it is absent from every shipping client's query string, so a request carrying it is hand-rolled, not a client that needs an error.