fix(test): use ephemeral port for ExtensionLifecycleIntegrationTest

testOnMethodUnattended in BTraceFunctionalTests leaks its target JVM
process without stopping it, leaving the BTrace agent bound to port
2020 indefinitely. ExtensionLifecycleIntegrationTest then fails with
"Port 2020 unavailable" because the port is never released.

Fix by adding btracePort field to RuntimeTest that passes -p <port>
to the btrace Loader, and using ServerSocket(0) in the lifecycle tests
to pick a fresh ephemeral port for each test, avoiding the conflict
entirely.

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

Author: jbachorik

integration-tests/src/test/java/tests/ExtensionLifecycleIntegrationTest.java

@@ -24,6 +24,7 @@
  */
 package tests;
 
+import java.io.IOException;
 import java.net.ServerSocket;
 import org.junit.jupiter.api.BeforeAll;
 import org.junit.jupiter.api.BeforeEach;
@@ -49,29 +50,12 @@ public static void setup() throws Exception {
   @Override
   public void reset() {
     super.reset();
-    waitForPort(2020, 30_000);
-  }
-
-  /**
-   * Waits until the given port is available (not in use by a previous test's agent).
-   */
-  private static void waitForPort(int port, long timeoutMs) {
-    long deadline = System.currentTimeMillis() + timeoutMs;
-    while (System.currentTimeMillis() < deadline) {
-      try (ServerSocket ss = new ServerSocket(port)) {
-        ss.setReuseAddress(true);
-        return; // port is free
-      } catch (Exception e) {
-        // port still in use
-        try {
-          Thread.sleep(200);
-        } catch (InterruptedException ie) {
-          Thread.currentThread().interrupt();
-          return;
-        }
-      }
+    // Use an ephemeral port to avoid conflicts with leaked agents from other test classes
+    try (ServerSocket ss = new ServerSocket(0)) {
+      btracePort = ss.getLocalPort();
+    } catch (IOException e) {
+      throw new RuntimeException("Failed to find a free port", e);
     }
-    System.err.println("WARNING: port " + port + " still unavailable after " + timeoutMs + "ms");
   }
 
   @Test
@@ -89,7 +73,7 @@ public void validate(String stdout, String stderr, int retcode, String jfrFile)
             // Validate extension method was called
             assertTrue(
                 stdout.contains("LIFECYCLE: extension method called"),
-                "Extension method not called");
+                "Extension method not called. stdout: " + stdout);
           }
         });
   }
@@ -107,9 +91,10 @@ public void validate(String stdout, String stderr, int retcode, String jfrFile)
             // Extension should still be called even on error exit
             assertTrue(
                 stdout.contains("LIFECYCLE: extension method called"),
-                "Extension method not called");
+                "Extension method not called. stdout: " + stdout);
             assertTrue(
-                stdout.contains("Triggering error exit"), "Error exit message not found");
+                stdout.contains("Triggering error exit"),
+                "Error exit message not found. stdout: " + stdout);
           }
         });
   }
@@ -129,10 +114,10 @@ public void validate(String stdout, String stderr, int retcode, String jfrFile)
             // Validate both extensions were called
             assertTrue(
                 stdout.contains("LIFECYCLE: printer extension called"),
-                "Printer extension method not called");
+                "Printer extension method not called. stdout: " + stdout);
             assertTrue(
                 stdout.contains("LIFECYCLE: metrics extension called"),
-                "Metrics extension method not called");
+                "Metrics extension method not called. stdout: " + stdout);
           }
         });
   }

integration-tests/src/test/java/tests/RuntimeTest.java

@@ -95,6 +95,8 @@ public abstract class RuntimeTest {
   protected boolean dumpOneliner = false;
   /** Dump verifier errors in target JVM */
   protected boolean dumpVerifierErrors = false;
+  /** Override the BTrace agent/client port (0 = use default 2020) */
+  protected int btracePort = 0;
   /** Provide extra JVM args */
   private static final List<String> extraJvmArgs = new ArrayList<>();
 
@@ -218,6 +220,7 @@ protected void reset() {
     attachDelayMs = 0;
     dumpOneliner = false;
     dumpVerifierErrors = false;
+    btracePort = 0;
     timeout = defaultTimeoutMs;
   }
 
@@ -1305,6 +1308,10 @@ private Process attach(
     if (unattended) {
       argVals.add("-x");
     }
+    if (btracePort > 0) {
+      argVals.add("-p");
+      argVals.add(String.valueOf(btracePort));
+    }
     argVals.addAll(Arrays.asList(pid, traceFile.getAbsolutePath()));
     if (cmdArgs != null) {
       argVals.addAll(Arrays.asList(cmdArgs));
@@ -1424,6 +1431,10 @@ private Process attachOneliner(
     if (unattended) {
       argVals.add("-x");
     }
+    if (btracePort > 0) {
+      argVals.add("-p");
+      argVals.add(String.valueOf(btracePort));
+    }
     argVals.addAll(Arrays.asList(pid));
     if (cmdArgs != null) {
       argVals.addAll(Arrays.asList(cmdArgs));