Type alias MountMap

MountMap: {
    [T in UpdateType]: Extract<Update, Record<T, object>>
} & {
    [T in MessageSubType]: {
        message: ExtractPartial<Update.MessageUpdate["message"], Record<T, unknown>>;
        update_id: number;
    }
}

Maps [[Composer.on]]'s updateType or messageSubType to a tt.Update subtype.