diff --git a/include/utils/simple_json.h b/include/utils/simple_json.h
index 1235d21..9b9767b 100644
--- a/include/utils/simple_json.h
+++ b/include/utils/simple_json.h
@@ -80,11 +80,12 @@ public:
         return static_cast<int>(AsNumber(static_cast<double>(def)));
     }
 
-    const std::string& AsString(const std::string& def = EmptyString()) const {
+    // NOTE: Return by value to avoid lifetime issues when callers pass temporaries as defaults.
+    std::string AsString(std::string_view def = {}) const {
         if (const auto* s = std::get_if<std::string>(&value_)) {
             return *s;
         }
-        return def;
+        return std::string(def);
     }
 
     const Array& AsArray() const {
@@ -134,11 +135,6 @@ public:
 
 private:
     Variant value_;
-
-    static const std::string& EmptyString() {
-        static const std::string empty;
-        return empty;
-    }
 };
 
 inline void SkipWhitespace(std::string_view text, size_t& pos) {
diff --git a/src/graph_manager.cpp b/src/graph_manager.cpp
index a06b649..7c95af6 100644
--- a/src/graph_manager.cpp
+++ b/src/graph_manager.cpp
@@ -1142,29 +1142,34 @@ bool GraphManager::BuildFromFile(const std::string& path, std::string& err) {
 }
 
 bool GraphManager::StartAll() {
-    std::lock_guard<std::mutex> lock(graphs_mu_);
+    std::scoped_lock lock(mu_, graphs_mu_);
+    if (running_) return true;
+
+    // Start all graphs; on failure, stop any already started graphs so we never leave a partially-running state.
+    std::vector<Graph*> started;
+    started.reserve(graphs_.size());
     for (auto& g : graphs_) {
+        if (!g) continue;
         if (!g->Start()) {
+            for (auto* sg : started) {
+                if (sg) sg->Stop();
+            }
             return false;
         }
+        started.push_back(g.get());
     }
-    {
-        std::lock_guard<std::mutex> lock(mu_);
-        running_ = true;
-    }
+
+    running_ = true;
     return true;
 }
 
 void GraphManager::StopAll() {
     {
-        std::lock_guard<std::mutex> lock(mu_);
+        std::scoped_lock lock(mu_, graphs_mu_);
         if (!running_) return;
         running_ = false;
-    }
-    {
-        std::lock_guard<std::mutex> lock(graphs_mu_);
         for (auto& g : graphs_) {
-            g->Stop();
+            if (g) g->Stop();
         }
     }
     cv_.notify_all();