v4: hydration doesn't restore a static value that changes on the browser

[gtm-nayan]

Describe the bug

I'm guessing this is related to #7426.

Two SvelteKit tests started failing with version 4 as reported by ecosystem-ci, both of them were using the BROWSER variable from esm-env to display different content on the browser than on the server.

The compiler perceives the condition variable to be static and the generated code doesn't attempt to restore the html to the actual value at that moment.

Reproduction

https://github.com/sveltejs/svelte/tree/v4-hydration-bug

git clone https://github.com/sveltejs/svelte/tree/v4-hydration-bug
cd svelte/packages/playground
pnpm i
pnpm dev

Go to localhost:10001

Logs

None

System Info

n/a

Severity

blocking an upgrade

[benmccann]

fixed in #8744