Issue with Flattened Tagged Unions When Using "Pick"

export const ExternalCalendarEvent = Schema.Union( // Discriminated on a field named source
  CancelledCalendarEvent,
  HotelCalendarEvent,
);
export type ExternalCalendarEvent = typeof ExternalCalendarEvent.Type;

export type ExternalEventSource = Pick<
  ExternalCalendarEvent,
  "source" | "metadata"
>;

type ExternalEventSource = {
    readonly source: "cancelled" | "hotel-event";
    readonly metadata: {
        readonly a: string;
    } | {
        readonly b: string;
    };
}

type ExternalEventSource = {
    readonly source: "hotel-event";
    readonly metadata: {
        readonly a: string;
    }
} | {
    readonly source: "cancelled" 
    readonly metadata: {
        readonly b: string;
    };
}