remote function underscore does nothing

Describe the bug

The docs say that adding an underscore prevents the value from being sent back to the user. This does not happen, values with underscores are still repopulated in the input.

Reproduction

+page.svelte:
`<script>
import { register } from '$lib/register.remote';
</script>

Username

<label>
	Password
	<input {...register.fields._password.as('password')} />
</label>

<button>Sign up!</button>

`

register.remote.ts:
`import * as v from 'valibot'
import {form} from '$app/server'
import { invalid } from '@sveltejs/kit'

export const register = form(v.object({
username: v.string(),
_password: v.string()
}), async ({username, _password }) => {
invalid('invalid credentials')
})`

Logs

System Info

System:
    OS: macOS 15.4.1
    CPU: (8) x64 Intel(R) Core(TM) i5-1038NG7 CPU @ 2.00GHz
    Memory: 1.20 GB / 16.00 GB
    Shell: 5.9 - /bin/zsh
  Binaries:
    Node: 25.2.1 - /usr/local/bin/node
    npm: 11.6.2 - /usr/local/bin/npm
    pnpm: 10.8.0 - /usr/local/bin/pnpm
    bun: 1.2.8 - /Users/matteopiatti/.bun/bin/bun
  Browsers:
    Chrome: 142.0.7444.177
    Firefox: 142.0.1
    Safari: 18.4
  npmPackages:
    @sveltejs/adapter-auto: ^7.0.0 => 7.0.0 
    @sveltejs/kit: ^2.49.2 => 2.49.2 
    @sveltejs/vite-plugin-svelte: ^6.2.1 => 6.2.1 
    svelte: ^5.43.8 => 5.45.8 
    vite: ^7.2.2 => 7.2.7

Severity

annoyance

Additional Information

No response

Start with the provided +page.svelte and register.remote.ts reproduction, then trace SvelteKit's remote-function form handling to see where underscore-prefixed fields are serialized or repopulated. Add a regression test for the _password field and verify that submitting an invalid form does not send its value back to the user.