fix: race condition when importing AsyncLocalStorage

[elliott-with-the-longest-name-on-github]

Closes #17345 -- basically if you get the timings actually perfectly right it appears you get two copies of ALS, one which gets used for the first half of the first render and another that gets used for every subsequent render (including the second half of the first render, which causes the error). I have no idea how to test this other than running the reproduction in the original issue, which this fixes. (@florian-lefebvre, can you verify as well? Thanks!)

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pnpm add https://pkg.pr.new/svelte@17350

[matthewp]

This still looks racey to me. Maybe it's not actually possible to have a race due to how this code is used that I don't have context for, but in isolation if init_render_context where called twice sequentially there would be 2 instances of als created. Maybe that doesn't matter because by the time its used there's only 1. I think what this code is really attempting to do is memoize the result of the full init_render_context() call.

[Rich-Harris]

Yeah, maybe this?

/** @type {AsyncLocalStorage<RenderContext> | null} */
let als = null;

/** @type {Promise<void> | null} */
let als_promise = null;

export function init_render_context() {
	als_promise ??= import('node:async_hooks')
		.then((hooks) => {
			als = new hooks.AsyncLocalStorage();
		})
		.catch(noop);

	return als_promise;
}

[elliott-with-the-longest-name-on-github]

lol, one step ahead of you

[matthewp]

Can confirm this fixes the Astro test that was breaking. Thanks a lot!

[elliott-with-the-longest-name-on-github]

that somehow broke everything, brb