Function use_optimistic 

pub fn use_optimistic<A, R, D>(
    mutation: Mutation<A, R>,
    subscription: Signal<SubscriptionState<D>>,
    apply: impl Fn(&D, &A) -> D + 'static,
) -> OptimisticMutation<A, R, D>
where
    A: Serialize + Clone + 'static,
    R: DeserializeOwned + 'static,
    D: Clone + PartialEq + 'static,

Create an optimistic mutation that layers local patches over a live subscription. Returns an OptimisticMutation whose .data() reflects the optimistic state and whose .fire() applies the transform, sends the mutation, and auto-reverts on error or TTL expiry.

let reorder = use_optimistic(
    use_reorder_task(),
    use_list_tasks_live_signal(),
    |tasks, args: &ReorderTaskInput| {
        tasks.iter().map(|t| {
            if t.id == args.id { Task { status: args.status, position: args.position, ..t.clone() } }
            else { t.clone() }
        }).collect()
    },
);
// Read from reorder.data() instead of the raw subscription
// Call reorder.fire(args) for optimistic + server mutation