Remove url.full from default OpenTelemetry metrics attributes (#2815)

## Summary
- Remove `url.full` from default OpenTelemetry metrics request
attributes to avoid high-cardinality metric explosion
- Users who need the full URL can opt in via
`OpenTelemetryDefaults.requestAttributesWithFullUrl`
- Add tests verifying `url.full` is absent by default and present when
explicitly opted in

## Test plan
- [ ] Verify new tests pass: default attributes exclude `url.full`,
`requestAttributesWithFullUrl` includes it

🤖 Generated with [Claude Code](https://claude.com/claude-code)

Co-authored-by: Claude Opus 4.6 <noreply@anthropic.com>

Author: adamw

observability/opentelemetry-backend/src/main/scala/sttp/client4/opentelemetry/OpenTelemetryDefaults.scala

@@ -3,7 +3,6 @@ package sttp.client4.opentelemetry
 import sttp.client4.GenericRequest
 import io.opentelemetry.api.common.Attributes
 import io.opentelemetry.semconv.HttpAttributes
-import sttp.client4.Response
 import io.opentelemetry.semconv.UrlAttributes
 import io.opentelemetry.semconv.ErrorAttributes
 import io.opentelemetry.semconv.ServerAttributes
@@ -28,7 +27,6 @@ object OpenTelemetryDefaults {
   private def requestAttributesBuilder(request: GenericRequest[_, _]): AttributesBuilder =
     Attributes.builder
       .put(HttpAttributes.HTTP_REQUEST_METHOD, request.method.method)
-      .put(UrlAttributes.URL_FULL, request.uri.toString())
       .put(ServerAttributes.SERVER_ADDRESS, request.uri.host.getOrElse("unknown"))
       .put(ServerAttributes.SERVER_PORT, request.uri.port.getOrElse(80))
 

observability/opentelemetry-backend/src/test/scala/sttp/client4/opentelemetry/OpenTelemetryMetricsBackendTest.scala

@@ -276,6 +276,42 @@ class OpenTelemetryMetricsBackendTest extends AnyFlatSpec with Matchers with Opt
       .find(_.getName.equals(name))
       .head
 
+  it should "not include url.full in default request attributes to avoid high cardinality" in {
+    // given
+    val reader = InMemoryMetricReader.create()
+    val backend = OpenTelemetryMetricsBackend(stubAlwaysOk, spawnNewOpenTelemetry(reader))
+
+    // when
+    basicRequest.get(uri"http://127.0.0.1/foo?bar=1").send(backend)
+
+    // then
+    val metrics = reader.collectAllMetrics().asScala.toList
+    val metric = metrics.find(_.getName == OpenTelemetryMetricsBackend.DefaultLatencyHistogramName).value
+    metric.getHistogramData.getPoints.forEach { point =>
+      point.getAttributes.get(AttributeKey.stringKey("url.full")) shouldBe null
+    }
+  }
+
+  it should "include url.full when using requestAttributesWithFullUrl" in {
+    // given
+    val reader = InMemoryMetricReader.create()
+    val config = OpenTelemetryMetricsConfig(
+      spawnNewOpenTelemetry(reader),
+      requestAttributes = OpenTelemetryDefaults.requestAttributesWithFullUrl _
+    )
+    val backend = OpenTelemetryMetricsBackend(stubAlwaysOk, config)
+
+    // when
+    basicRequest.get(uri"http://127.0.0.1/foo?bar=1").send(backend)
+
+    // then
+    val metrics = reader.collectAllMetrics().asScala.toList
+    val metric = metrics.find(_.getName == OpenTelemetryMetricsBackend.DefaultLatencyHistogramName).value
+    metric.getHistogramData.getPoints.forEach { point =>
+      point.getAttributes.get(AttributeKey.stringKey("url.full")) shouldBe "http://127.0.0.1/foo?bar=1"
+    }
+  }
+
   private[this] def specTest(metrics: List[MetricData], expectedMetricName: String): Unit = {
     val metric = metrics.find(_.getName == expectedMetricName)
     assert(