IsTraceRoot is a tristate

Author: amarziali

dd-trace-core/src/main/java/datadog/trace/common/metrics/SerializingMetricWriter.java

@@ -118,7 +118,7 @@ public void add(MetricKey key, AggregateMetric aggregate) {
     writer.writeBoolean(key.isSynthetics());
 
     writer.writeUTF8(IS_TRACE_ROOT);
-    writer.writeBoolean(key.isTraceRoot());
+    writer.writeInt(key.isTraceRoot() ? 1 : 2); // tristate (0 unknown, 1 true, 2 false)
 
     writer.writeUTF8(SPAN_KIND);
     writer.writeUTF8(key.getSpanKind());

dd-trace-core/src/test/groovy/datadog/trace/common/metrics/SerializingMetricWriterTest.groovy

@@ -177,7 +177,7 @@ class SerializingMetricWriterTest extends DDSpecification {
         assert unpacker.unpackBoolean() == key.isSynthetics()
         ++elementCount
         assert unpacker.unpackString() == "IsTraceRoot"
-        assert unpacker.unpackBoolean() == key.isTraceRoot()
+        assert unpacker.unpackInt() == (key.isTraceRoot() ? 1 : 2)
         ++elementCount
         assert unpacker.unpackString() == "SpanKind"
         assert unpacker.unpackString() == key.getSpanKind() as String