Deterministic render ordering

src/metric.hpp

@@ -218,6 +218,11 @@ bool is_valid_metric_name(std::string_view name);
 bool is_valid_label_key(std::string_view key);
 bool is_valid_label_value(std::string_view value);
 
+// Reset all metrics state - WARNING: Only safe for testing!
+// This clears all registered families and metrics. Should only be called
+// when no metric objects are in use and no concurrent render() calls.
+void reset_metrics_for_testing();
+
 // Note: Histograms do not support callbacks due to their multi-value nature
 // (buckets + sum + count). Use static histogram metrics only.