OptionalDefaultDefault maximum results if not specified in SearchParams (default: 20)
OptionalDefaultDefault multiplier applied to per-provider topK to compensate for residual
late permission filtering. A scope's ScopeConfig.permissionOverfetchFactor or a call's
SearchParams.PermissionOverfetchFactor takes precedence. Clamped to 1–20 (logged once, at
configuration); a non-finite value falls back to 2. Default: 2.
Configuration options for the SearchEngine.