OpenAI strict mode rejects optional properties in nested objects #327

OpenAILanguageModel and OpenResponsesLanguageModel send structured output schemas with strict: true. OpenAI's strict mode requires every property of every object to be in required, with a null type for an optional one. toJSONValueForOpenAIStrictMode() and toJSONValueForOpenResponsesStrictMode() only do this for the root object, so an optional property in a nested object is left out of required.

For example, unit isn't in Address's required here:

@Generable
struct Contact {
    var name: String
    var address: Address
}

@Generable
struct Address {
    var street: String
    var unit: String?
}

The same goes for enum cases with optional values, like case note(String?) (#322).

The fix is probably to apply the root's rules to every object in the schema, and make each optional property's type nullable.