Fix fanout naming for debug graph

include/kpn/fanout.hpp

@@ -51,9 +51,10 @@ public:
     using return_tuple = detail::repeat_tuple_t<T, N>;
     using return_raw   = return_tuple;
 
-    static constexpr std::size_t input_count  = 1;
-    static constexpr std::size_t output_count = N;
-    static constexpr std::size_t unique_tag   = Id;
+    static constexpr std::size_t input_count    = 1;
+    static constexpr std::size_t output_count   = N;
+    static constexpr std::size_t unique_tag     = Id;
+    static constexpr bool        is_fanout_node = true;
 
     explicit FanoutNode(std::size_t fifo_capacity = 5)
         : fifo_capacity_(fifo_capacity)

include/kpn/main_thread_node.hpp

@@ -101,9 +101,9 @@ public:
     }
 
     template<std::size_t I>
-    InputPort<MainThreadNode, I> input() {
+    InputPort<Derived, I> input() {
         static_assert(I < input_count, "input index out of range");
-        return {*this};
+        return {static_cast<Derived&>(*this)};
     }
 
     template<fixed_string Name>

include/kpn/static_network.hpp

@@ -72,6 +72,8 @@ std::string node_display_name() {
     constexpr std::string_view lbl = node_label_v<NodeT>;
     if constexpr (!lbl.empty()) {
         return std::string(lbl);
+    } else if constexpr (requires { NodeT::is_fanout_node; NodeT::unique_tag; }) {
+        return "fanout[" + std::to_string(NodeT::unique_tag) + "]";
     } else if constexpr (requires { NodeT::unique_tag; }) {
         return "node[" + std::to_string(NodeT::unique_tag) + "]";
     } else {
@@ -261,6 +263,29 @@ auto make_network(Edges&&... edges) {
         return ptr;
     };
 
+    // Pre-pass: build fanout_id → source display name map so fanout nodes
+    // can be named after the node feeding them (e.g. "capture_fanout").
+    std::map<std::size_t, std::string> fanout_src_name;
+    [&]<typename... SEs>(tmp::TypeList<SEs...>) {
+        ([&]<typename SE>(SE) {
+            using DstNode = typename SE::dst_node_t;
+            using SrcNode = typename SE::src_node_t;
+            if constexpr (requires { DstNode::is_fanout_node; })
+                fanout_src_name.emplace(DstNode::unique_tag, node_display_name<SrcNode>());
+        }(SEs{}), ...);
+    }(ExpandedEdges{});
+
+    // Helper: display name for any node type, resolving fanouts to "src_fanout".
+    auto node_name = [&]<typename NodeT>() -> std::string {
+        if constexpr (requires { NodeT::is_fanout_node; }) {
+            auto it = fanout_src_name.find(NodeT::unique_tag);
+            return it != fanout_src_name.end() ? it->second + "_fanout"
+                                               : node_display_name<NodeT>();
+        } else {
+            return node_display_name<NodeT>();
+        }
+    };
+
     std::vector<std::unique_ptr<IChannelProbe>> channel_probes;
 
     auto wire_one = [&]<typename SE>(SE) {
@@ -275,9 +300,9 @@ auto make_network(Edges&&... edges) {
         if (src && dst) {
             auto& ch = dst->template input_channel<DstIdx>();
             src->template set_output_channel<SrcIdx>(&ch);
-            std::string ch_name = node_display_name<SrcNode>() + ":" + std::to_string(SrcIdx)
+            std::string ch_name = node_name.template operator()<SrcNode>() + ":" + std::to_string(SrcIdx)
                                 + " \xe2\x86\x92 "  // UTF-8 →
-                                + node_display_name<DstNode>() + ":" + std::to_string(DstIdx);
+                                + node_name.template operator()<DstNode>() + ":" + std::to_string(DstIdx);
             channel_probes.push_back(std::make_unique<ChannelProbe<out_t>>(ch, ch_name));
         }
     };
@@ -291,8 +316,9 @@ auto make_network(Edges&&... edges) {
     std::vector<std::string> fanout_node_names;
     std::apply([&](auto&... fn) {
         ([&](auto& node) {
+            using NodeT = std::decay_t<decltype(node)>;
             fanout_ptrs.push_back(static_cast<INode*>(&node));
-            fanout_node_names.push_back(node_display_name<std::decay_t<decltype(node)>>());
+            fanout_node_names.push_back(node_name.template operator()<NodeT>());
         }(fn), ...);
     }, *fanout_storage);