Data returned from action inside /login is not serializable: Cannot stringify arbitrary non-POJOs

[Bishwas-py]

[FORMS-ACTIONS] Returning something inside fail is giving me the upper error;

return fail(500, {
    message: 'Something went wrong.',
    message_type: 'error',
    alias: 'internal_server_error'
});

but while returning

{
message: 'Something went wrong.',
message_type: 'error',
alias: 'internal_server_error'
}

it works.

It used to work, maybe upgrading on Svelte 5 made something weird here?

Here's what I've been trying to do,

export const via_route_name = (proxy_paths, opt_ = {}) => {
    const action = {
        ['login']: async (event) => {
            // return {
            //                 message: 'Something went wrong.',
            //                 message_type: 'error',
            //                 alias: 'internal_server_error'
            //             }; this works
            return fail(500, {
                message: 'Something went wrong.',
                message_type: 'error',
                alias: 'internal_server_error'
            }); // this doesn't
        }
    }
    return {
        ...action
    }
};

in +page.server.ts

export const actions = via_route_name(['login'], {allow_cookies: true})

via_route_name is a proxy, and it return actions. There are conditions attached to via_route_name function, but I have reduced it to simplify the issue.

[Bishwas-py]

Kit related issue: sveltejs/kit#12287