Add new key value pair at top level of paginated collection

Hello, I am trying to work out how to add a new key value pair at the top level of a paginated collection. I have been trying to work this out, as I have an object that has been flashed to the session in a method that redirects back to the method in which I am trying to inject it's values into the paginated collection. I can have worked out how to add it to each item in the collection.data, using the following:

        // map the collection to be returned and add the 'new' key to the array at the top level
        $threads->getCollection()->transform(function ($thread) {
            return array_merge($thread, ['new' => (bool)session('show'),]);
        });

However, this is annoying as it is adding it to each item & will return way more data than I need.

I had the idea that maybe paginating the collection after the query has been performed & somehow injecting the key value pair at this point, but I would not know how to do that either.

I really need to work this out, can you help me?

This is the full method currently:

    public function index()
    {

        $threads = Thread::query()
            ->select('*')
            ->with('creator:id,username,email')
            ->with(['replies' => function ($query) {
                $query->select('replies.id', 'replies.thread_id', 'replies.body', 'replies.created_at', 'replies.updated_at', 'replies.user_id')
                    ->with('owner:id,username,email')
                    ->leftJoin('users', 'users.id', '=', 'replies.user_id');
            }])
            ->latest()
            ->paginate(20)
            ->through(function ($thread) {
                $firstReply = $thread->replies->first();
                return [
                    'title' => $thread->title,
                    'body' => $thread->body,
                    'slug' => $thread->slug,
                    'views' => $thread->views,
                    'solved' => $thread->solved,
                    'created_at' => $thread->created_at->diffForHumans(null),
                    'replies' => $thread->replies->count() ? [
                        'count' => $thread->replies->count(),
                        'first' => [
                            'body' => $firstReply->body,
                            'created_at' => $firstReply->created_at->diffForHumans(null),
                            'updated_at' => $firstReply->updated_at->diffForHumans(null),
                            'owner' => [
                                'username' => $firstReply->owner->username,
                                'email' => $firstReply->owner->email,
                            ]
                        ],
                    ] : null,
                    'creator' => [
                        'username' => $thread->creator->username,
                        'email' => $thread->creator->email,
                    ],

                ];
            });

        // map the collection to be returned and add the 'new' key to the array at the top level
        $threads->getCollection()->transform(function ($thread) {
            return array_merge($thread, ['new' => (bool)session('show'),]);
        });

        return Inertia::render('Discussion/Index', [
            'conversations' => $threads,
        ]);

    }