Type Alias ModuleResult<O, A>

ModuleResult: O extends Fields
    ? OneKey<O> extends true
        ? ValueOf<O[keyof O]>
        : { [K in keyof O]: ValueOf<O[K]> }
    : A extends FieldSpec ? ValueOf<A> : never

What a module returns: its one output's value (output, or outputs naming one), or its several outputs by name (programs.md, "Checking values": one output is the value).