feat(go-adk): propagate A2A message metadata as OTEL span attributes

go/adk/pkg/a2a/executor.go

@@ -138,6 +138,8 @@ func (e *KAgentExecutor) Execute(ctx context.Context, reqCtx *a2asrv.RequestCont
 	ctx, invocationSpan := telemetry.StartInvocationSpan(ctx)
 	defer invocationSpan.End()
 
+	telemetry.SetMessageMetadataAttributes(ctx, reqCtx.Message.Metadata)
+
 	// 3. Initialize skills session path.
 	if e.skillsDirectory != "" && sessionID != "" {
 		if _, err := skills.InitializeSessionPath(sessionID, e.skillsDirectory); err != nil {

go/adk/pkg/telemetry/attributes.go

@@ -3,6 +3,7 @@ package telemetry
 import (
 	"context"
 	"encoding/json"
+	"fmt"
 	"os"
 	"strings"
 
@@ -87,6 +88,32 @@ func stringAttributes(attrs map[string]string) []attribute.KeyValue {
 	return out
 }
 
+// SetMessageMetadataAttributes sets scalar values from an A2A message's metadata as span attributes.
+func SetMessageMetadataAttributes(ctx context.Context, metadata map[string]any) {
+	if len(metadata) == 0 {
+		return
+	}
+	var attrs []attribute.KeyValue
+	for k, v := range metadata {
+		key := "a2a.message.metadata." + k
+		switch val := v.(type) {
+		case string:
+			if val != "" {
+				attrs = append(attrs, attribute.String(key, val))
+			}
+		case bool:
+			attrs = append(attrs, attribute.Bool(key, val))
+		case float64:
+			attrs = append(attrs, attribute.String(key, fmt.Sprintf("%g", val)))
+		case int:
+			attrs = append(attrs, attribute.Int(key, val))
+		case int64:
+			attrs = append(attrs, attribute.Int64(key, val))
+		}
+	}
+	setSpanAttributes(ctx, attrs...)
+}
+
 func setSpanAttributes(ctx context.Context, attrs ...attribute.KeyValue) {
 	span := trace.SpanFromContext(ctx)
 	if !span.IsRecording() || len(attrs) == 0 {

go/adk/pkg/telemetry/attributes_test.go

@@ -2,6 +2,7 @@ package telemetry
 
 import (
 	"context"
+	"strings"
 	"testing"
 
 	"go.opentelemetry.io/otel"
@@ -170,6 +171,76 @@ func TestSetLLMAttributes_EmitsEmptyPayloadWhenContentCaptureDisabled(t *testing
 	}
 }
 
+func TestSetMessageMetadataAttributes(t *testing.T) {
+	exporter := tracetest.NewInMemoryExporter()
+	tp := sdktrace.NewTracerProvider(sdktrace.WithSyncer(exporter))
+	t.Cleanup(func() { _ = tp.Shutdown(context.Background()) })
+
+	tracer := tp.Tracer("test")
+	ctx, span := tracer.Start(context.Background(), "test-span")
+
+	SetMessageMetadataAttributes(ctx, map[string]any{
+		"approver_email": "admin@example.com",
+		"attempt_count":  float64(3),
+		"dry_run":        true,
+		"nested":         map[string]any{"should": "be skipped"},
+		"list_val":       []string{"also", "skipped"},
+		"empty_str":      "",
+	})
+	span.End()
+
+	spans := exporter.GetSpans()
+	if len(spans) == 0 {
+		t.Fatal("no spans recorded")
+	}
+	attrs := make(map[string]attribute.Value)
+	for _, a := range spans[0].Attributes {
+		attrs[string(a.Key)] = a.Value
+	}
+
+	if got := attrs["a2a.message.metadata.approver_email"].AsString(); got != "admin@example.com" {
+		t.Errorf("approver_email: got %q, want %q", got, "admin@example.com")
+	}
+	if got := attrs["a2a.message.metadata.attempt_count"].AsString(); got != "3" {
+		t.Errorf("attempt_count: got %q, want %q", got, "3")
+	}
+	if got := attrs["a2a.message.metadata.dry_run"].AsBool(); !got {
+		t.Errorf("dry_run: got %v, want true", got)
+	}
+	if _, exists := attrs["a2a.message.metadata.nested"]; exists {
+		t.Error("nested map should not be set as span attribute")
+	}
+	if _, exists := attrs["a2a.message.metadata.list_val"]; exists {
+		t.Error("list value should not be set as span attribute")
+	}
+	if _, exists := attrs["a2a.message.metadata.empty_str"]; exists {
+		t.Error("empty string should not be set as span attribute")
+	}
+}
+
+func TestSetMessageMetadataAttributes_NilAndEmpty(t *testing.T) {
+	exporter := tracetest.NewInMemoryExporter()
+	tp := sdktrace.NewTracerProvider(sdktrace.WithSyncer(exporter))
+	t.Cleanup(func() { _ = tp.Shutdown(context.Background()) })
+
+	tracer := tp.Tracer("test")
+	ctx, span := tracer.Start(context.Background(), "test-span")
+
+	SetMessageMetadataAttributes(ctx, nil)
+	SetMessageMetadataAttributes(ctx, map[string]any{})
+	span.End()
+
+	spans := exporter.GetSpans()
+	if len(spans) == 0 {
+		t.Fatal("no spans recorded")
+	}
+	for _, a := range spans[0].Attributes {
+		if strings.HasPrefix(string(a.Key), "a2a.message.metadata.") {
+			t.Errorf("no metadata attributes expected, got %q", a.Key)
+		}
+	}
+}
+
 func spanAttributesByName(t *testing.T, spans tracetest.SpanStubs, name string) map[string]attribute.Value {
 	t.Helper()