### Summary `dist/clients/core/params.ts` in `@hey-api/openapi-ts` ships a runtime template that is copied verbatim into every generated SDK as `params.gen.ts`. When a caller passes an object argument containing an unknown key starting with a slot prefix (`$body_`, `$headers_`, `$path_`, `$query_`), the function strips the prefix and writes the remainder directly to that slot without validation. The key `"$query___proto__"` causes the returned `params.query` object to have its prototype chain s