Options of `<select multiple={true}>` have incorrect `selected` property value

[Bladesheng]

Describe the bug

When you set the multiple attribute on <select> element dynamically (e.g. with some variable, or a function), the children <option> elements will always have selected property value equal to false, even when they have selected attribute.

Reproduction

https://svelte.dev/playground/97cac4d339644901b93d6e289d054bd4?version=5.45.2

As you can see, the first 2 <select> have correctly preselected the first 2 options, but the other selects have only 1 option selected.
The selected attributes are set correctly, but the properties are not.

System Info

Chrome 142.0.7444.175
Svelte 5.45.2

Severity

blocking an upgrade

[Bladesheng]

One workaround for now is to use some action (or attachment) like this, that will check the attribute value and change the property value:

<script lang="ts">
import type {Action} from 'svelte/action';

const fixOptionsSelected: Action<HTMLSelectElement> = (node) => {
	node.querySelectorAll('option').forEach((option) => {
		if (typeof option.getAttribute('selected') === 'string') {
			option.selected = true;
		} else {
			option.selected = false;
		}
	});
}
</script>

<select id="fifth" multiple={isMultiple ? 'multiple' : null} use:fixOptionsSelected>
	<option value="1" selected>one</option>
	<option value="2" selected>two</option>
	<option value="3">three</option>
</select>