feat: load pipeline graph from graph.json

studio-manager now accepts an optional path argument:
  dmf-studio-manager graph.json

load_graph() parses nodes and edges from JSON, generating fresh UUIDs
for each MXL flow on every launch. Falls back to hardcoded build_graph()
when no argument is given.

graph.json at repo root defines the current testpattern→ndiout pipeline.

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

graph.json

@@ -0,0 +1,18 @@
+{
+  "nodes": [
+    { "id": "testpattern", "type": "testpattern", "params": { "pattern": "bars" } },
+    { "id": "ndiout",      "type": "ndiout",      "params": {} }
+  ],
+  "edges": [
+    {
+      "from": "testpattern", "from_port": "flow_id",
+      "to":   "ndiout",      "to_port":   "flow_id",
+      "format": { "kind": "video", "width": 1920, "height": 1080, "fps_num": 25, "fps_den": 1 }
+    },
+    {
+      "from": "testpattern", "from_port": "audio_flow_id",
+      "to":   "ndiout",      "to_port":   "audio_flow_id",
+      "format": { "kind": "audio", "sample_rate": 48000, "channels": 2, "bit_depth": 32 }
+    }
+  ]
+}

studio-manager/main.cpp

@@ -5,6 +5,8 @@
 #include <cstdio>
 #include <cstdlib>
 #include <filesystem>
+#include <fstream>
+#include <sstream>
 #include <string>
 #include <vector>
 #include <fcntl.h>
@@ -37,6 +39,45 @@ static std::string gen_uuid() {
 
 // --- Pipeline graph ----------------------------------------------------------
 
+static dmf::FlowGraph load_graph(const std::string& path) {
+    std::ifstream f(path);
+    if (!f) {
+        fprintf(stderr, "[studio-manager] cannot open graph file: %s\n", path.c_str());
+        exit(1);
+    }
+    std::ostringstream ss;
+    ss << f.rdbuf();
+
+    auto j = nlohmann::json::parse(ss.str(), nullptr, /*allow_exceptions=*/false);
+    if (j.is_discarded()) {
+        fprintf(stderr, "[studio-manager] invalid JSON in %s\n", path.c_str());
+        exit(1);
+    }
+
+    dmf::FlowGraph g;
+    for (const auto& n : j.at("nodes")) {
+        g.nodes.push_back({
+            n.at("id").get<std::string>(),
+            n.at("type").get<std::string>(),
+            n.value("params", nlohmann::json::object())
+        });
+    }
+    for (const auto& e : j.at("edges")) {
+        g.edges.push_back({
+            gen_uuid(),
+            e.at("from").get<std::string>(),
+            e.at("from_port").get<std::string>(),
+            e.value("to",      std::string{}),
+            e.value("to_port", std::string{}),
+            e.at("format")
+        });
+    }
+
+    fprintf(stderr, "[studio-manager] loaded graph from %s (%zu nodes, %zu edges)\n",
+        path.c_str(), g.nodes.size(), g.edges.size());
+    return g;
+}
+
 static dmf::FlowGraph build_graph() {
     dmf::FlowGraph g;
     const std::string tp_video_flow = gen_uuid();
@@ -164,7 +205,7 @@ int main(int argc, char* argv[]) {
     }
 
     // --- Build and launch the pipeline graph ---
-    const dmf::FlowGraph graph = build_graph();
+    const dmf::FlowGraph graph = (argc > 1) ? load_graph(argv[1]) : build_graph();
 
     for (const auto& e : graph.edges)
         fprintf(stderr, "[studio-manager] flow %s → %s  id=%s\n",