Server loader with cache headers can't cache first load

Describe the bug

If I have cache headers set in my server load function

export async function load(params) {
	console.log('LOADING');

	// const val = params.url.searchParams.get('val');
	const val = params.url.search;

	const result = {
		searchProps: 'Value ' + val + ' ' + ' CACHE TEST VALUE === ' + i++
	};

	params.setHeaders({
		'cache-control': 'max-age=60'
		//Vary: 'Cookie'
	});

	return result;
}

the headers work, and the page is cached, but if I start on this page, browse elsewhere, and then hit the back button, the loader re-runs.

The reason appears to be that the initial load of my site renders the entire page (which does have the correct headers), but subsequent navigations fetch a __data.js with the right url attached, so browsing back to it fetches that, which isn't (yet) cached.

Reproduction

The minimal repro is here: https://github.com/arackaf/booklist/tree/special/bug-repro/svelte-kit

the directory above that has a huge project around it, but that directory I've linked to contains a minimal SvelteKit app that reproduces this (ostensible) bug.

It's currently deployed here: https://booklist-svelte-kit.vercel.app/

As you navigate, you'll see fresh calls to fetch __data.json, even when you click back to the starting page, which, again, is not (yet) cached.

Logs

No response

System Info

System:
    OS: macOS 12.6
    CPU: (16) x64 Intel(R) Core(TM) i9-9980HK CPU @ 2.40GHz
    Memory: 149.78 MB / 16.00 GB
    Shell: 5.8.1 - /bin/zsh
  Binaries:
    Node: 16.14.2 - /usr/local/Cellar/nvm/0.38.0/versions/node/v16.14.2/bin/node
    Yarn: 1.22.17 - /usr/local/Cellar/nvm/0.38.0/versions/node/v16.11.1/bin/yarn
    npm: 8.18.0 - ~/Documents/node_modules/.bin/npm
  Browsers:
    Chrome: 107.0.5304.110
    Firefox: 107.0
  npmPackages:
    @sveltejs/adapter-auto: next => 1.0.0-next.89 
    @sveltejs/kit: next => 1.0.0-next.557 
    svelte: ^3.44.0 => 3.53.1 
    vite: ^3.1.0 => 3.2.4

Severity

serious, but I can work around it

Additional Information

No response

Start with the linked minimal SvelteKit reproduction and compare the initial page request with the subsequent __data.js request during back navigation. Trace how cache-control headers from the server load function apply to each request; done means returning to the starting page uses the cached response without rerunning the loader.