State not rerendering in reusable reactivity logic

[faizwong]

Describe the bug

This bug seems to happen starting version 5.34.4

Consider a very simple example

<!-- App.svelte -->

<script>
	import createCounter from "./createCounter.svelte.ts"

	const counter = createCounter()
</script>

<button onclick={counter.increment}>Count: {counter.count}</button>

// createCounter.svelte.ts

const createCounter = () => {
	let count = $state(0)

	const increment = () => {
		count += 1;
	}

	return {
		get count() {
			return count
		},
		increment
	}
}

export default createCounter

Prior to version 5.34.4, this will work as expected. 5.34.4 onwards, the count state never rerenders upon increment.

Reproduction

Compare these two behaviors in two different versions. One is working (5.34.3) and one is not (5.34.4)

https://svelte.dev/playground/be9f1fb951b44427a98dd736af9a7b1d?version=5.34.3

https://svelte.dev/playground/be9f1fb951b44427a98dd736af9a7b1d?version=5.34.4

Logs

System Info

System:
    OS: macOS 14.6
    CPU: (8) arm64 Apple M3
    Memory: 307.73 MB / 16.00 GB
    Shell: 5.9 - /bin/zsh
  Binaries:
    Node: 22.16.0 - ~/.nvm/versions/node/v22.16.0/bin/node
    npm: 10.9.2 - ~/.nvm/versions/node/v22.16.0/bin/npm
  Browsers:
    Brave Browser: 137.1.79.126
    Chrome: 137.0.7151.120
    Safari: 17.6
  npmPackages:
    svelte: ^5.0.0 => 5.34.7

Severity

blocking an upgrade

[faizwong]

Might be a duplicate of #16199