How to compile a single .svelte file from a SvelteKit app as a web component?

I have a SvelteKit 2/Svelte 5 app with out-of-the-box configuration - what you get by running npx sv create my-app. I want to build my app normally with adapter-node, but I also want to build a single .svelte file as a web component that I can reuse in other projects.

Currently my setup is this:

// $lib/widget/MyComponent.svelte<svelte:options    customElement={{        tag: 'my-component',    }}/><script lang="ts">    let counter = $state(0)</script><button onclick={() => (counter += 1)}>    Clicked {counter} times</button>

// svelte.config.jsimport { mdsvex } from 'mdsvex'import adapter from '@sveltejs/adapter-node'import { vitePreprocess } from '@sveltejs/vite-plugin-svelte'const config = {    preprocess: [vitePreprocess(), mdsvex()],    kit: {        adapter: adapter(),    },    extensions: ['.svelte', '.svx'],}export default config

// vite.widget.config.tsimport { svelte } from '@sveltejs/vite-plugin-svelte'export default {    build: {        lib: {            entry: 'src/lib/widget/MyComponent.svelte',            name: 'MyComponent',            fileName: (format) => `my-component.${format}.js`,            formats: ['es'],        },        rollupOptions: {            external: ['svelte'],            output: {                globals: {                    svelte: 'svelte',                },            },        },        sourcemap: 'inline',    },    plugins: [        svelte({            compilerOptions: {                customElement: true,            },        }),    ],}

vite build --config vite.widget.config.ts

<!-- root/my-component.html --><my-component></my-component><script src="./dist/my-component.es.js" type="module"></script>

It works, but I'm not sure if this is the correct way to do it.

I'm getting a warning in my .svelte file that I haven't specified customElement: true, but that's because I have my compiler options in vite.widget.config.ts.

I tried looking at the svelte/compiler docs, but I couldn't understand how I'm supposed to use that module.

Any tips are welcome!