Combinable closed-catalog query. Scope required. Row-capped. Cursor-paginated.

Provide a closed q, named slots, or a structured catalog filter; supplied controls combine with AND and are validated through the builder whitelist. A field not held by the scoped county returns an honest empty. Exactly one of scope.fips, scope.state, or scope.held is required; scope.held=[all] searches loaded non-Vermont counties. Omit-select rows include the 91 canonical_fields in schema order; unheld values are null. A named select keeps the requested keys and is not forced to 91. Metering: charges search (1) on accept and record_reveal per returned row. scope_coverage describes requested geography versus schema-bindable counties, independently of positive/zero rows and pagination. State scope uses the pinned current Census spine plus loaded historical counties, explicitly marked legacy. Wholly unloaded scope returns 400 county-not-held, not field-not-held or no matches.