The issue

When running this project in dev mode, you should see that both values are properly updated.

sveltekit: npm run dev -- --open viteonly: npm run dev -- --open

When running this project in build mode, you should see that only the second value is properly updated.

sveltekit: npm run build && npm run preview viteonly: npm run build && npm run serve

Why

It looks like the spread operator is expanding the state variable once but does not keep the original state getter reference.

This might only happen in the build because of a compile-time optimization on the spread operator, but at this point, I can't figure out the exact details.