(Svelte 4) subscribed store in markup won't use module instance

[theetrain]

Describe the bug

In a component with <script context="module">, some markup, and without <script>; having a writable store be set by an exported function won't cause reactive updates in the markup.

Adding an empty <script></script> will include writable store in compiled output.

Reproduction

Toast component: https://svelte.dev/repl/6c0757bed5044018ba5560733e7b56bf?version=4.2.19

1. Click on button labelled "Click me"
2. Observe empty Toast message

Workaround:

1. Add <script></script> to the markup
2. Observe new prop in compiled output (there are more changes in compiled output as well):

/* Toast.svelte generated by Svelte v4.2.19 */
import {
  SvelteComponent,
  append,
  append_styles,
  attr,
  component_subscribe,
  detach,
  element,
  init,
  insert,
  noop,
  safe_not_equal,
+ set_data,
+ text as text_1,
  toggle_class
} from "svelte/internal";

3. Click button to present a working Toast message

Note this works totally fine in Svelte 5, in both Runes and non-Runes modes. Demo.

Logs

No response

System Info

Svelte 4.2.19

Severity

annoyance

[Conduitry]

Closing, as this works in v5.