The agents the user may run: DecisionDiscoveryRunnableAgents over the engine's catalog.
OptionalDeclaredThe decision model's option cap (DecisionPromptOptionCap), when one is declared.
OptionalHostThe host's allow-list (HostAllowedAgentIDs), when the run carries one.
The agent running discovery, such as Sage. It is never an option.
OptionalSearchNarrows a catalog over the limit. Undefined when the provider cannot run the search.
What BuildDecisionDiscoveryOptionSet builds the Choice's options from.