ClickHouseQuerySchemaAdapter

What a dataset's table proves about its declaration (design §4.2, §5.2). The declaration is the contract and the table only confirms it: every declared field must be a root column of a supported type whose family matches the declared types, a non-null declaration needs a non-Nullable column, and the scope and identity columns must not be Nullable. FINAL needs an engine that merges rows. Any mismatch fails the compile, so the Catalog keeps the previous schema and reports it; a column the declaration does not name is never exposed.