Fix smoke test failures by replacing Spring Boot plugin with Shadow

Co-authored-by: xiang17 <9310587+xiang17@users.noreply.github.com>

Author: Copilot

buildSrc/build.gradle.kts

@@ -43,7 +43,4 @@ dependencies {
 
   implementation("gradle.plugin.io.morethan.jmhreport:gradle-jmh-report:0.9.6")
   implementation("me.champeau.jmh:jmh-gradle-plugin:0.7.3")
-
-  // Spring Boot 3.5+ is required for Gradle 9 compatibility
-  implementation("org.springframework.boot:spring-boot-gradle-plugin:3.5.10")
 }

buildSrc/src/main/kotlin/ai.smoke-test-jar.gradle.kts

@@ -1,11 +1,25 @@
+import com.github.jengelman.gradle.plugins.shadow.tasks.ShadowJar
 import com.microsoft.applicationinsights.gradle.AiSmokeTestExtension
 
 plugins {
   id("ai.smoke-test")
-  id("org.springframework.boot")
+  id("com.gradleup.shadow")
 }
 
 val aiSmokeTest = extensions.getByType(AiSmokeTestExtension::class)
 
-aiSmokeTest.testAppArtifactDir.set(tasks.bootJar.flatMap { it.destinationDirectory })
-aiSmokeTest.testAppArtifactFilename.set(tasks.bootJar.flatMap { it.archiveFileName })
+// Create a fat JAR using Shadow instead of Spring Boot plugin for Gradle 9 compatibility
+// Spring Boot 2.x doesn't support Gradle 9, and Spring Boot 3.x requires Java 17+
+// Shadow creates a simple fat JAR that works with Java 8
+tasks.named<ShadowJar>("shadowJar") {
+  archiveClassifier.set("")
+  mergeServiceFiles()
+  
+  // Use the standard main class convention for smoke test apps
+  manifest {
+    attributes["Main-Class"] = "com.microsoft.applicationinsights.smoketestapp.SpringBootApp"
+  }
+}
+
+aiSmokeTest.testAppArtifactDir.set(tasks.shadowJar.flatMap { it.destinationDirectory })
+aiSmokeTest.testAppArtifactFilename.set(tasks.shadowJar.flatMap { it.archiveFileName })