Function dispatch_ready_tool_cancellable 

pub async fn dispatch_ready_tool_cancellable(
    dispatcher: &Arc<TransactionToolDispatcher>,
    exchange_id: ExchangeId,
    tool_action_id: ToolActionId,
    tool_name: &str,
    provider_tool_call_id: &str,
    request_ordinal: u32,
    arguments_json: &str,
    cancel: Option<Arc<StickyCancel>>,
) -> DispatchOutcome

Dispatch with an actor-owned cancel signal so mid-dispatch cancel joins the worker (D-028).