chore: phase 1 cleanup — proper shutdown, flow resource cleanup, test fix

- node_runner: track all readers/writers in flow_resources vector,
  release them via mxlReleaseFlowWriter/mxlReleaseFlowReader before
  destroying the MXL instance (fixes 'leaked flow writer' warning)
- node_runner: remove_writer/remove_reader commands now also release
  the MXL flow resources, not just reset the node's optional<>
- engine: call process_manager.stop_all(graph) on shutdown to kill
  child node processes (prevents orphaned passthrough processes)
- graph: add get_node_mut() for process_manager to update node state
- process_manager: implement stop_all(Graph&) that SIGTERMs all
  running node processes
- passthrough: reduce logging to first-grain and realign-once only
- tests: update flow format assertion to match NMOS
  (urn:x-nmos:format:video instead of video/v210)

libs/dmf-node/src/node_runner.cpp

@@ -94,7 +94,14 @@ int NodeRunner::exec(std::unique_ptr<Node> node) {
         return arr;
     };
 
-    control_server->register_command("add_writer", [&, w = std::unordered_map<std::string, mxlFlowWriter>{}](const nlohmann::json& msg) mutable {
+    struct FlowResource {
+        std::string port_id;
+        mxlFlowWriter writer = nullptr;
+        mxlFlowReader reader = nullptr;
+    };
+    std::vector<FlowResource> flow_resources;
+
+    control_server->register_command("add_writer", [&](const nlohmann::json& msg) {
         auto flow_id = msg["flow_id"].get<std::string>();
         auto port_id = msg["port_id"].get<std::string>();
         auto flow_def = msg["flow_def"].dump();
@@ -108,6 +115,7 @@ int NodeRunner::exec(std::unique_ptr<Node> node) {
             return;
         }
         spdlog::info("Created flow writer on port '{}' flow {} (created={})", port_id, flow_id, created);
+        flow_resources.push_back({port_id, writer, nullptr});
         node->on_add_writer(port_id, writer);
     });
 
@@ -122,18 +130,33 @@ int NodeRunner::exec(std::unique_ptr<Node> node) {
             return;
         }
         spdlog::info("Created flow reader on port '{}' flow {}", port_id, flow_id);
+        flow_resources.push_back({port_id, nullptr, reader});
         node->on_add_reader(port_id, reader);
     });
 
     control_server->register_command("remove_writer", [&](const nlohmann::json& msg) {
         auto port_id = msg["port_id"].get<std::string>();
         node->on_remove_writer(port_id);
+        for (auto it = flow_resources.begin(); it != flow_resources.end(); ++it) {
+            if (it->port_id == port_id && it->writer) {
+                mxlReleaseFlowWriter(mxl_instance_, it->writer);
+                flow_resources.erase(it);
+                break;
+            }
+        }
         spdlog::info("Removed writer on port '{}'", port_id);
     });
 
     control_server->register_command("remove_reader", [&](const nlohmann::json& msg) {
         auto port_id = msg["port_id"].get<std::string>();
         node->on_remove_reader(port_id);
+        for (auto it = flow_resources.begin(); it != flow_resources.end(); ++it) {
+            if (it->port_id == port_id && it->reader) {
+                mxlReleaseFlowReader(mxl_instance_, it->reader);
+                flow_resources.erase(it);
+                break;
+            }
+        }
         spdlog::info("Removed reader on port '{}'", port_id);
     });
 
@@ -184,6 +207,17 @@ int NodeRunner::exec(std::unique_ptr<Node> node) {
     process_thread.join();
 
     spdlog::info("Node '{}' shutting down", node_id_);
+
+    for (auto& res : flow_resources) {
+        if (res.writer) {
+            mxlReleaseFlowWriter(mxl_instance_, res.writer);
+        }
+        if (res.reader) {
+            mxlReleaseFlowReader(mxl_instance_, res.reader);
+        }
+    }
+    flow_resources.clear();
+
     mxlDestroyInstance(mxl_instance_);
     return 0;
 }