Address code review feedback: improve tests, use type-safe OTel detection, and remove redundant code

Author: vcjana

aws/codegen-aws-sdk/src/main/kotlin/software/amazon/smithy/rustsdk/AwsCodegenDecorator.kt

@@ -46,6 +46,7 @@ val DECORATORS: List<ClientCodegenDecorator> =
             CredentialsProviderDecorator(),
             RegionDecorator(),
             RequireEndpointRules(),
+            EndpointOverrideDecorator(),
             UserAgentDecorator(),
             SigV4AuthDecorator(),
             HttpRequestChecksumDecorator(),
@@ -65,7 +66,6 @@ val DECORATORS: List<ClientCodegenDecorator> =
             AwsRequestIdDecorator(),
             DisabledAuthDecorator(),
             RecursionDetectionDecorator(),
-            EndpointOverrideDecorator(),
             ObservabilityDetectionDecorator(),
             InvocationIdDecorator(),
             RetryInformationHeaderDecorator(),

aws/codegen-aws-sdk/src/test/kotlin/software/amazon/smithy/rustsdk/EndpointOverrideDecoratorTest.kt

@@ -67,16 +67,7 @@ class EndpointOverrideDecoratorTest {
     }
 
     @Test
-    fun `generated code includes endpoint override interceptor registration`() {
-        awsSdkIntegrationTest(model) { _, _ ->
-            // The test passes if the code compiles successfully
-            // This verifies that the decorator generates valid Rust code
-        }
-    }
-
-    @Test
-    fun `generated code compiles with endpoint override interceptor`() {
-        // Create custom test params with endpoint_url config enabled
+    fun `endpoint override interceptor adds business metric to user agent`() {
         val testParams =
             awsIntegrationTestParams().copy(
                 additionalSettings =
@@ -94,22 +85,58 @@ class EndpointOverrideDecoratorTest {
         awsSdkIntegrationTest(model, testParams) { context, rustCrate ->
             val rc = context.runtimeConfig
             val moduleName = context.moduleUseName()
-            rustCrate.integrationTest("endpoint_override_compiles") {
-                tokioTest("can_build_client_with_endpoint_url") {
+            rustCrate.integrationTest("endpoint_override_functional") {
+                tokioTest("interceptor_adds_metric_when_endpoint_overridden") {
                     rustTemplate(
                         """
                         use $moduleName::config::Region;
                         use $moduleName::{Client, Config};
 
-                        let (http_client, _rcvr) = #{capture_request}(#{None});
+                        let (http_client, rcvr) = #{capture_request}(#{None});
                         let config = Config::builder()
                             .region(Region::new("us-east-1"))
                             .endpoint_url("https://custom.example.com")
                             .http_client(http_client.clone())
-                            .with_test_defaults()
                             .build();
-                        let _client = Client::from_conf(config);
-                        // Test passes if code compiles and client can be created
+                        let client = Client::from_conf(config);
+
+                        // CRITICAL: Actually make a request
+                        let _ = client.some_operation().send().await;
+
+                        // Capture and verify the request
+                        let request = rcvr.expect_request();
+
+                        // Verify endpoint was overridden
+                        let uri = request.uri().to_string();
+                        assert!(
+                            uri.starts_with("https://custom.example.com"),
+                            "Expected custom endpoint, got: {}",
+                            uri
+                        );
+
+                        // Verify x-amz-user-agent contains business metric 'N' (endpoint override)
+                        // The metric appears in the business-metrics section as "m/..." with comma-separated IDs
+                        let x_amz_user_agent = request.headers()
+                            .get("x-amz-user-agent")
+                            .expect("x-amz-user-agent header missing");
+
+                        // Extract the business metrics section (starts with "m/")
+                        let has_endpoint_override_metric = x_amz_user_agent
+                            .split_whitespace()
+                            .find(|part| part.starts_with("m/"))
+                            .map(|metrics| {
+                                // Check if 'N' appears as a metric ID (either alone or in a comma-separated list)
+                                metrics.strip_prefix("m/")
+                                    .map(|ids| ids.split(',').any(|id| id == "N"))
+                                    .unwrap_or(false)
+                            })
+                            .unwrap_or(false);
+
+                        assert!(
+                            has_endpoint_override_metric,
+                            "Expected metric ID 'N' (endpoint override) in x-amz-user-agent business metrics, got: {}",
+                            x_amz_user_agent
+                        );
                         """,
                         *preludeScope,
                         "capture_request" to RuntimeType.captureRequest(rc),