Updates not persisting

export const sessionsCollection = createCollection(
    queryCollectionOptions({
        queryKey: [QUERY_KEY_OWNED_SESSIONS],
        queryFn: async () => listSessionsServerFn({}),
        schema: ActiveSessionSchema,
        queryClient,
        getKey: (item) => item.id,
        onInsert: async ({ transaction }) => {
            const newItem = transaction.mutations[0].modified;
            const saved = await insertSessionServerFn({ data: newItem });
            return { upsert: [saved] };
        },
        onUpdate: async ({ transaction }) => {
            const mutation = transaction.mutations[0].modified;
            console.log('mutation', mutation);

            const updated = await updateSessionServerFn({ data: mutation });
            return { upsert: [updated], refetch: false };
        },
        onDelete: async ({ transaction }) => {
            const id = transaction.mutations[0].key;
            await deleteSessionServerFn({ data: { sessionId: id } });
            return { remove: [id], refetch: false };
        },
    })
);

... later
const tx = sessionsCollection.update('id_12345' (draft) => {
    return {
        ...draft,
        ...form.getValues(),
    };
});
await tx.isPersisted.promise;