Choose the public configuration and UX surface

[iam-brain]

Question

What public surface, if any, should be added for Ultra beyond the catalog-derived reasoning variant?

Decide with the maintainer:

• whether Ultra is purely a catalog variant or also needs a feature flag, delegation policy, concurrency setting, warning preference, or explicit enablement;
• default behavior in existing installations and compatibility with global.reasoningEffort, per-model overrides, per-variant overrides, and customModels;
• model-picker naming, ordering, descriptions, disabled-state explanations, and distinction from Max;
• whether Sol and Terra require separate wording or share one contract;
• schema/type/loader/examples/documentation implications of every proposed field;
• whether any field would expose an internal catalog/runtime default that repository policy says should remain private;
• migration behavior for users who already configured literal reasoningEffort: "ultra";
• how warnings and fallback states are surfaced without noisy repetition.

The resolution should select the smallest coherent public surface and enumerate every documentation/config artifact it affects.