Add static network

include/kpn/network.hpp

@@ -12,6 +12,7 @@
 #include <iomanip>
 #include <iostream>
 #include <map>
+#include <set>
 #include <sstream>
 #include <stdexcept>
 #include <string>
@@ -87,6 +88,13 @@ public:
         if (!src) throw NetworkBuildError("node '" + src_name + "' type mismatch");
         if (!dst) throw NetworkBuildError("node '" + dst_name + "' type mismatch");
 
+        auto port_key = std::make_pair(src_name, SrcIdx);
+        if (connected_outputs_.count(port_key))
+            throw NetworkBuildError(
+                "connect: output port '" + src_name + "':" + std::to_string(SrcIdx)
+                + " is already connected — use make_fanout<T, N> for fan-out");
+        connected_outputs_.insert(port_key);
+
         auto& in_ch = dst->template input_channel<DstIdx>();
         src->template set_output_channel<SrcIdx>(&in_ch);
 
@@ -321,6 +329,7 @@ private:
     std::vector<std::string>                               topo_;
     std::map<std::string, std::string>                     exposed_inputs_;
     std::map<std::string, std::string>                     exposed_outputs_;
+    std::set<std::pair<std::string, std::size_t>>          connected_outputs_;
     std::vector<std::unique_ptr<IChannelProbe>>            channel_probes_;
     ErrorHandler                                           error_handler_;
     DiagnosticsHandler                                     diag_handler_;