`toStore` and reactive variables (legacy)

[aMediocreDad]

Describe the bug

Stores created with toStore show inconsistent behaviour when passed as a prop togther with and without the state it was initialized with.

<!-- Parent -->
<!-- If use the input we will observe no reactivity in the child component. -->
<script>
  import { toStore } from "svelte/store"

  import Child from './Component.svelte'
	
  let state = $state({ nested: "Nested Text" })
</script>
<p>Change me: <input bind:value={state.nested} /></p>

<Child store={toStore(() => state)} {state}></Child>

<!-- Child -->
<!-- However if we uncomment the commented out code in the child component we will now
  observe that the {text} variable and the chained reference in the template are reactive
--> 
<svelte:options runes={false} />

<script>
  export let store;
  //export let state;

  $: derived = $store.nested || "nested"
  //$: text = state.nested || "state"
</script>

<p>I am a template chained reference: {$store.nested}</p>
<p>I am a derived variable: {derived}</p>
<!-- <p>I am propped state derived: {text}</p> -->

Expected behaviour is reactivity in both cases where toStore is used. If not possible, consistency is at least expected.

Reproduction

REPL Here: https://svelte.dev/playground/5c4215385e8c49d98e0b45ce2a63f7a8?version=latest

Logs

N/A

System Info

N/A

Severity

blocking all usage of svelte

[aMediocreDad]

The reason why I set the severity at the level I did is that this is blocking a progressive migration to Svelte 5. The usecase here is for a store that gets passed down to grandchildren as context in a +page.svelte component. The +page.svelte has migrated to Svelte 5, however all the grandchildren that are still Svelte 4 expects a store with nested properties. The issue was first discovered when migrating like this:

...
const store = writable(...data)
setContext('key', store)

// to

...
const state = $state(...data)
setContext('key', toStore(() => state))