Function heartbeat_response_handler_executor 

pub fn heartbeat_response_handler_executor(
    extensions: &FrontendHeartbeatExtensions,
    suspend_state: Arc<AtomicBool>,
    cache_invalidator: CacheInvalidatorRef,
) -> HeartbeatResponseHandlerExecutorRef

Builds the frontend heartbeat response handler chain.

Mailbox parsing always runs first, followed by extension handlers, suspension state handling, and cache invalidation.