`defaultChecked` does not work in form remote functions

[hyunbinseo]

Describe the bug

<script lang="ts">
  import { FormSchema } from './ids';
  import { addId } from './ids.remote';
</script>

<form {...addId.preflight(FormSchema)}>
  <fieldset>
    {#each ['windows', 'mac', 'linux'] as os, index}
      <label>
        <!-- windows is not checked -->
        <input {...addId.fields.operatingSystem.as('radio', os)} defaultChecked={!index} />
        {os}
      </label>
    {/each}
  </fieldset>
  <fieldset>
    {#each ['windows', 'mac', 'linux'] as os, index}
      <label>
        <!-- windows is checked -->
        <input type="radio" name="os" value={os} defaultChecked={!index} />
        {os}
      </label>
    {/each}
  </fieldset>
</form>

Happens on both Firefox and Chrome.

<form method="POST" action="?/remote=14dkmo%2FaddId">
  <fieldset>
    <!-- dev tools shows that it is checked, but the UI does not reflect this -->
    <label><input name="operatingSystem" type="radio" value="windows" checked="" /> windows</label
    ><label><input name="operatingSystem" type="radio" value="mac" /> mac</label
    ><label><input name="operatingSystem" type="radio" value="linux" /> linux</label>
  </fieldset>
  <fieldset>
    <label><input type="radio" name="os" value="windows" checked="" /> windows</label
    ><label><input type="radio" name="os" value="mac" /> mac</label
    ><label><input type="radio" name="os" value="linux" /> linux</label>
  </fieldset>
</form>

Reproduction

https://github.com/hyunbinseo/svelte-kit-template/tree/mre-kit-14707

Logs

System Info

System:
  OS: Windows 11 10.0.26100
  CPU: (8) x64 Intel(R) Core(TM) Ultra 7 258V
  Memory: 3.51 GB / 31.48 GB
Binaries:
  Node: 24.10.0 - C:\Users\hyunb\AppData\Local\fnm_multishells\24580_1760341048510\node.EXE
  Yarn: 1.22.22 - C:\Users\hyunb\AppData\Local\fnm_multishells\24580_1760341048510\yarn.CMD
  npm: 11.6.1 - C:\Users\hyunb\AppData\Local\fnm_multishells\24580_1760341048510\npm.CMD
  pnpm: 10.18.2 - C:\Users\hyunb\AppData\Local\fnm_multishells\24580_1760341048510\pnpm.CMD
  Deno: 2.4.0 - C:\Users\hyunb\.deno\bin\deno.EXE
Browsers:
  Chrome: 141.0.7390.76
  Edge: Chromium (140.0.3485.54)
  Firefox: 143.0.4 - C:\Program Files\Mozilla Firefox\firefox.exe
npmPackages:
  @sveltejs/adapter-auto: ^6.1.1 => 6.1.1 
  @sveltejs/kit: ^2.46.5 => 2.46.5 
  @sveltejs/vite-plugin-svelte: ^6.2.1 => 6.2.1 
  svelte: ^5.39.11 => 5.39.11 
  vite: ^7.1.7 => 7.1.7

Severity

blocking an upgrade

Additional Information

No response

[DipakHalkude]

Is this added as a bug?