Added callbacks for node errors and fifo overflow

Add new doc system which should/might deploy to pages.

include/kpn/static_network.hpp

@@ -112,6 +112,16 @@ public:
     void start() override {
         stop_flag_ = false;
         start_time_ = clock_t::now();
+        if (event_handler_) {
+            for (std::size_t i = 0; i < user_nodes_topo_.size(); ++i) {
+                auto* node = user_nodes_topo_[i];
+                const auto& n = user_node_names_[i];
+                node->set_network_overflow_callback(
+                    [this, n](auto ts) { event_handler_(n, NodeEvent::Overflow, ts); });
+                node->set_network_closed_callback(
+                    [this, n](auto ts) { event_handler_(n, NodeEvent::Closed, ts); });
+            }
+        }
         for (auto* n : user_nodes_topo_)  n->start();
         for (auto* n : fanout_nodes_ptr_) n->start();
 #ifdef KPN_WEB_DEBUG
@@ -165,6 +175,12 @@ public:
         return {n, 0, 0, 0, 0, 0, 0, 0};
     }
 
+    using EventHandler =
+        std::function<void(std::string_view node_name, NodeEvent,
+                           std::chrono::steady_clock::time_point)>;
+
+    void set_event_handler(EventHandler h) { event_handler_ = std::move(h); }
+
 #ifdef KPN_WEB_DEBUG
     void set_web_debug_port(uint16_t port) { web_debug_port_ = port; }
     // Called by DebugHub::register_network() so the hub owns the debug server.
@@ -259,6 +275,7 @@ private:
     std::vector<std::unique_ptr<IChannelProbe>>         channel_probes_;
     std::vector<std::pair<std::string, IResourceProbe*>> resource_probes_;
     std::vector<std::pair<std::string, IPoolProbe*>>     pool_probes_;
+    EventHandler                                        event_handler_;
     clock_t::time_point                                 start_time_;
 #ifdef KPN_WEB_DEBUG
     uint16_t                                            web_debug_port_{9090};