fix(o11y): create noop tracer when artifact ID is not set (#12307)

## Description

This PR ensures that fallback logic is consistently applied across
observability tracers when the client library metadata—specifically the
`artifactName`—is omitted or invalid. If the `artifactName` is missing,
the factories will safely return a no-op (base) tracer.

### Key Changes
- Added an early return in
`GoldenSignalsMetricsTracerFactory.withContext()` to fallback to
`BaseApiTracerFactory` when the `ApiTracerContext` or `artifactName` is
missing, mirroring `SpanTracerFactory`.
- Increased testing coverage in `SpanTracerFactoryTest` and
`GoldenSignalsMetricsTracerFactoryTest` to explicitly validate tracer
initialization under empty and null metadata conditions.

Author: diegomarquezp

sdk-platform-java/gax-java/gax/src/main/java/com/google/api/gax/tracing/GoldenSignalsMetricsTracerFactory.java

@@ -29,8 +29,10 @@
  */
 package com.google.api.gax.tracing;
 
+import com.google.api.client.util.Strings;
 import com.google.api.core.BetaApi;
 import com.google.api.core.InternalApi;
+import com.google.api.gax.rpc.LibraryMetadata;
 import io.opentelemetry.api.OpenTelemetry;
 
 /**
@@ -74,6 +76,13 @@ public ApiTracer newTracer(ApiTracer parent, ApiTracerContext methodLevelTracerC
 
   @Override
   public ApiTracerFactory withContext(ApiTracerContext context) {
+    if (context == null) {
+      return new BaseApiTracerFactory();
+    }
+    LibraryMetadata metadata = context.libraryMetadata();
+    if (metadata == null || metadata.isEmpty() || Strings.isNullOrEmpty(metadata.artifactName())) {
+      return new BaseApiTracerFactory();
+    }
     this.clientLevelTracerContext = context;
     this.metricsRecorder =
         new GoldenSignalsMetricsRecorder(

sdk-platform-java/gax-java/gax/src/test/java/com/google/api/gax/tracing/GoldenSignalsMetricsTracerFactoryTest.java

@@ -33,6 +33,7 @@
 import static org.mockito.Answers.RETURNS_DEEP_STUBS;
 import static org.mockito.Mockito.*;
 
+import com.google.api.gax.rpc.LibraryMetadata;
 import io.opentelemetry.api.OpenTelemetry;
 import org.junit.jupiter.api.BeforeEach;
 import org.junit.jupiter.api.Test;
@@ -48,7 +49,10 @@ void setUp() {
 
   @Test
   void newTracerWithSpanName_shouldCreateTracer_ifMetricsRecorderIsNotNull() {
-    tracerFactory.withContext(ApiTracerContext.empty());
+    LibraryMetadata metadata =
+        LibraryMetadata.newBuilder().setArtifactName("gax-java").setVersion("1.0").build();
+    ApiTracerContext context = ApiTracerContext.newBuilder().setLibraryMetadata(metadata).build();
+    tracerFactory.withContext(context);
     ApiTracer actual =
         tracerFactory.newTracer(
             mock(ApiTracer.class), mock(SpanName.class), ApiTracerFactory.OperationType.Unary);
@@ -67,7 +71,8 @@ void newTracerWithSpanName_shouldCreateBaseTracer_ifMetricsRecorderIsNull() {
   void newTracerWithApiTracerContext_shouldMergeApiTracerContext() {
     ApiTracerContext clientLevelTracerContext = mock(ApiTracerContext.class, RETURNS_DEEP_STUBS);
     ApiTracerContext methodLevelTracerContext = mock(ApiTracerContext.class);
-    when(clientLevelTracerContext.libraryMetadata().artifactName()).thenReturn("does not matter");
+    when(clientLevelTracerContext.libraryMetadata().artifactName()).thenReturn("gax-java");
+    when(clientLevelTracerContext.libraryMetadata().isEmpty()).thenReturn(false);
     when(clientLevelTracerContext.merge(methodLevelTracerContext))
         .thenReturn(clientLevelTracerContext);
 
@@ -78,9 +83,50 @@ void newTracerWithApiTracerContext_shouldMergeApiTracerContext() {
     assertThat(actual).isInstanceOf(GoldenSignalsMetricsTracer.class);
   }
 
+  @Test
+  void testWithContext_nullContext_returnsBaseApiTracerFactory() {
+    GoldenSignalsMetricsTracerFactory factory =
+        new GoldenSignalsMetricsTracerFactory(OpenTelemetry.noop());
+    ApiTracerFactory factoryWithContext = factory.withContext(null);
+    assertThat(factoryWithContext).isInstanceOf(BaseApiTracerFactory.class);
+  }
+
+  @Test
+  void testWithContext_nullMetadata_returnsBaseApiTracerFactory() {
+    GoldenSignalsMetricsTracerFactory factory =
+        new GoldenSignalsMetricsTracerFactory(OpenTelemetry.noop());
+    ApiTracerFactory factoryWithContext = factory.withContext(ApiTracerContext.empty());
+    assertThat(factoryWithContext).isInstanceOf(BaseApiTracerFactory.class);
+  }
+
+  @Test
+  void testWithContext_emptyArtifactName_returnsBaseApiTracerFactory() {
+    GoldenSignalsMetricsTracerFactory factory =
+        new GoldenSignalsMetricsTracerFactory(OpenTelemetry.noop());
+    LibraryMetadata metadata =
+        LibraryMetadata.newBuilder().setArtifactName("").setVersion("1.0").build();
+    ApiTracerContext context = ApiTracerContext.newBuilder().setLibraryMetadata(metadata).build();
+
+    ApiTracerFactory factoryWithContext = factory.withContext(context);
+    assertThat(factoryWithContext).isInstanceOf(BaseApiTracerFactory.class);
+  }
+
+  @Test
+  void testWithContext_nullArtifactName_returnsBaseApiTracerFactory() {
+    GoldenSignalsMetricsTracerFactory factory =
+        new GoldenSignalsMetricsTracerFactory(OpenTelemetry.noop());
+    LibraryMetadata metadata = LibraryMetadata.newBuilder().setVersion("1.0").build();
+    ApiTracerContext context = ApiTracerContext.newBuilder().setLibraryMetadata(metadata).build();
+
+    ApiTracerFactory factoryWithContext = factory.withContext(context);
+    assertThat(factoryWithContext).isInstanceOf(BaseApiTracerFactory.class);
+  }
+
   @Test
   void newTracerWithApiTracerContext_shouldCreateBaseTracer_ifMetricsRecorderIsNull() {
-    ApiTracer actual = tracerFactory.newTracer(mock(ApiTracer.class), mock(ApiTracerContext.class));
+    GoldenSignalsMetricsTracerFactory factory =
+        new GoldenSignalsMetricsTracerFactory(OpenTelemetry.noop());
+    ApiTracer actual = factory.newTracer(mock(ApiTracer.class), mock(ApiTracerContext.class));
 
     assertThat(actual).isInstanceOf(BaseApiTracer.class);
   }

sdk-platform-java/gax-java/gax/src/test/java/com/google/api/gax/tracing/SpanTracerFactoryTest.java

@@ -347,6 +347,29 @@ void testWithContext_nullMetadata_returnsBaseApiTracerFactory() {
     assertThat(factoryWithContext).isInstanceOf(BaseApiTracerFactory.class);
   }
 
+  @Test
+  void testWithContext_emptyArtifactName_returnsBaseApiTracerFactory() {
+    SpanTracerFactory factory =
+        new SpanTracerFactory(openTelemetry, tracer, ApiTracerContext.empty());
+    LibraryMetadata metadata =
+        LibraryMetadata.newBuilder().setArtifactName("").setVersion("1.0").build();
+    ApiTracerContext context = ApiTracerContext.newBuilder().setLibraryMetadata(metadata).build();
+
+    ApiTracerFactory factoryWithContext = factory.withContext(context);
+    assertThat(factoryWithContext).isInstanceOf(BaseApiTracerFactory.class);
+  }
+
+  @Test
+  void testWithContext_nullArtifactName_returnsBaseApiTracerFactory() {
+    SpanTracerFactory factory =
+        new SpanTracerFactory(openTelemetry, tracer, ApiTracerContext.empty());
+    LibraryMetadata metadata = LibraryMetadata.newBuilder().setVersion("1.0").build();
+    ApiTracerContext context = ApiTracerContext.newBuilder().setLibraryMetadata(metadata).build();
+
+    ApiTracerFactory factoryWithContext = factory.withContext(context);
+    assertThat(factoryWithContext).isInstanceOf(BaseApiTracerFactory.class);
+  }
+
   @Test
   void testWithContext_nullTracer_returnsBaseApiTracerFactory() {
     OpenTelemetry mockOpenTelemetry = mock(OpenTelemetry.class);