Why can't I use any code organization tool for setting cookies?

[gcb]

Summary

I can' only avoid the "Cookies can only be modified in a Server Action or Route Handler" error if the call to .set() lives directly on the body of a server action.

I cannot use any kind of code organization, even a mere method is enough to throw the error. is this by design? (why?) Or do i have something wrong on my environment?

// client_component.tsx
'use client'
import { serverAction } from '@/components/serverAction';
...
const [state, submitAction, isPending] = useActionState(serverAction, null);


// serverAction.ts
'use server'
import { saveCookie } from '@lib/cookieutils';

function localSaveCookies(){
	const cookieStore = await cookies();
	await cookieStore.set('u', session, { // fails
}

export async function serverAction(prevState: string | null, post: FormData) {
	const cookieStore = await cookies();
	await cookieStore.set('u', session, { // WORKS

         localSaveCookies(); // fail
         saveCookies(); // fail
}

Additional information

next@15.2.5

Example

No response