v1: serialize span links as structured data and honor baggage tag config.

dd-trace-core/src/main/java/datadog/trace/common/writer/ddagent/TraceMapperV1.java

@@ -89,7 +89,7 @@ public void map(List<? extends CoreSpan<?>> trace, Writable writable) {
     }
 
     CoreSpan<?> firstSpan = trace.get(0);
-    firstSpan.processTagsAndBaggage(spanMetadata, false, false);
+    firstSpan.processTagsAndBaggageWithStructuredLinks(spanMetadata);
     Metadata firstSpanMeta = spanMetadata.metadata;
 
     // encoded fields: 1..7, but skipping #5, as not required by tracers and set by the agent.
@@ -128,7 +128,7 @@ private void encodeSpans(Writable writable, int fieldId, List<? extends CoreSpan
     Metadata meta = spanMetadata.metadata;
     for (CoreSpan<?> span : spans) {
       if (meta == null) {
-        span.processTagsAndBaggage(spanMetadata, false, false);
+        span.processTagsAndBaggageWithStructuredLinks(spanMetadata);
         meta = spanMetadata.metadata;
       }
       TagMap tags = meta.getTags();

dd-trace-core/src/main/java/datadog/trace/core/CoreSpan.java

@@ -98,8 +98,17 @@ default String getSpanKindString() {
 
   void processTagsAndBaggage(MetadataConsumer consumer);
 
-  void processTagsAndBaggage(
-      MetadataConsumer consumer, boolean injectLinksAsTags, boolean injectBaggageAsTags);
+  /**
+   * Variant of {@link #processTagsAndBaggage(MetadataConsumer)} for protocols that serialize span
+   * links as first-class structured data rather than tags. Baggage tag injection still follows the
+   * tracer configuration.
+   *
+   * <p>To simplify tests, by default delegating to {@link
+   * #processTagsAndBaggage(MetadataConsumer)}.
+   */
+  default void processTagsAndBaggageWithStructuredLinks(MetadataConsumer consumer) {
+    processTagsAndBaggage(consumer);
+  }
 
   T setSamplingPriority(int samplingPriority, int samplingMechanism);
 

dd-trace-core/src/main/java/datadog/trace/core/DDSpan.java

@@ -781,10 +781,8 @@ public void processTagsAndBaggage(final MetadataConsumer consumer) {
   }
 
   @Override
-  public void processTagsAndBaggage(
-      final MetadataConsumer consumer, boolean injectLinksAsTags, boolean injectBaggageAsTags) {
-    context.processTagsAndBaggage(
-        consumer, longRunningVersion, this, injectLinksAsTags, injectBaggageAsTags);
+  public void processTagsAndBaggageWithStructuredLinks(final MetadataConsumer consumer) {
+    context.processTagsAndBaggageWithStructuredLinks(consumer, longRunningVersion, this);
   }
 
   @Override

dd-trace-core/src/main/java/datadog/trace/core/DDSpanContext.java

@@ -1199,6 +1199,20 @@ void processTagsAndBaggage(
         consumer, longRunningVersion, restrictedSpan, injectLinksAsTags, injectBaggageAsTags);
   }
 
+  /**
+   * Serialize span links as first-class structured data rather than tags. While baggage tag
+   * injection keeps following the tracer configuration.
+   */
+  void processTagsAndBaggageWithStructuredLinks(
+      final MetadataConsumer consumer, int longRunningVersion, DDSpan restrictedSpan) {
+    processTagsAndBaggage(
+        consumer,
+        longRunningVersion,
+        restrictedSpan,
+        false, // injectLinksAsTags
+        injectBaggageAsTags);
+  }
+
   void processTagsAndBaggage(
       final MetadataConsumer consumer,
       int longRunningVersion,

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

@@ -245,9 +245,6 @@ class SimpleSpan implements CoreSpan<SimpleSpan> {
   @Override
   void processTagsAndBaggage(MetadataConsumer consumer) {}
 
-  @Override
-  void processTagsAndBaggage(MetadataConsumer consumer, boolean injectLinksAsTags, boolean injectBaggageAsTags) {}
-
   @Override
   SimpleSpan setSamplingPriority(int samplingPriority, int samplingMechanism) {
     return this