Wire your client against stable fixtures.

Sandbox boundary: only the request shapes below resolve. The candidate-list cursor selects its terminating second fixture page, while a testKind other than mastery_gate returns an empty terminal page to demonstrate server-enforced filtering. Other query parameters, the materialize body, and headers are accepted for client-shape testing but do not select data or trigger writes. Use this surface to prove request construction, parsing, rendering, branching, filtering, and cursor termination—not auth, tenancy, idempotency, freshness, or upstream integration.