fix(agent,client,tests): probe listing after disconnect and test isolation

- Add disconnecting flag to RemoteClient for immediate probe visibility
- Skip loadAgent when agent already running (check btrace.port)
- Add try-finally cleanup in tests to prevent port conflicts

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

Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>

Author: jbachorik

btrace-agent/src/main/java/org/openjdk/btrace/agent/RemoteClient.java

@@ -76,6 +76,7 @@ public Boolean apply(Command value) {
   private volatile Socket sock;
   private volatile ObjectInputStream ois;
   private volatile ObjectOutputStream oos;
+  private volatile boolean disconnecting;
 
   private final AtomicReferenceFieldUpdater<RemoteClient, Socket> sockUpdater =
       AtomicReferenceFieldUpdater.newUpdater(RemoteClient.class, Socket.class, "sock");
@@ -325,6 +326,8 @@ private boolean dispatchCommand(Command cmd, boolean isConnected) {
           }
         case Command.DISCONNECT:
           {
+            // Mark as disconnecting so listProbes() can find this probe
+            disconnecting = true;
             ((DisconnectCommand) cmd).setProbeId(id.toString());
             synchronized (output) {
               WireIO.write(output, cmd);
@@ -361,7 +364,7 @@ private boolean dispatchCommand(Command cmd, boolean isConnected) {
   }
 
   public boolean isDisconnected() {
-    return sock == null;
+    return disconnecting || sock == null;
   }
 
   @Override
@@ -388,6 +391,7 @@ protected void closeAll() throws IOException {
   }
 
   void reconnect(ObjectInputStream ois, ObjectOutputStream oos, Socket socket) throws IOException {
+    this.disconnecting = false;
     this.sock = socket;
     this.ois = ois;
     this.oos = oos;

btrace-client/src/main/java/org/openjdk/btrace/client/Client.java

@@ -472,6 +472,7 @@ public void attach(String pid, String agentPath, String sysCp, String bootCp) th
       }
       Properties serverVmProps = vm.getSystemProperties();
       int serverPort = Integer.parseInt(serverVmProps.getProperty("btrace.port", "-1"));
+      boolean agentAlreadyRunning = false;
       if (serverPort != -1) {
         if (serverPort != port) {
           throw new IOException(
@@ -483,12 +484,23 @@ public void attach(String pid, String agentPath, String sysCp, String bootCp) th
                   + serverPort
                   + "!");
         }
+        agentAlreadyRunning = true;
+        if (log.isDebugEnabled()) {
+          log.debug("agent already running on port {}", port);
+        }
       } else {
         if (!isPortAvailable(port)) {
           throw new IOException("Port " + port + " unavailable.");
         }
       }
 
+      if (agentAlreadyRunning) {
+        if (log.isDebugEnabled()) {
+          log.debug("skipping loadAgent, agent already active");
+        }
+        return;
+      }
+
       if (log.isDebugEnabled()) {
         log.debug("attached to {}", pid);
         log.debug("loading {}", agentPath);

btrace-client/src/main/java/org/openjdk/btrace/client/Main.java

@@ -314,12 +314,12 @@ public static void main(String[] args) throws Exception {
             createCommandListener(client),
             new String[] {probeCommand, probeCommandArg});
       } else if (listProbes) {
-        registerExitHook(client);
+        // Don't register exit hook for list-only operations - they shouldn't remove probes
         client.attach(pid.toString(), null, classPath);
         client.connectAndListProbes(host, createCommandListener(client));
         System.exit(0);
       } else if (listFailedExtensions) {
-        registerExitHook(client);
+        // Don't register exit hook for list-only operations - they shouldn't remove probes
         client.attach(pid.toString(), null, classPath);
         client.connectAndListFailedExtensions(host, createCommandListener(client));
         System.exit(0);

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

@@ -424,29 +424,41 @@ public void testOnMethodUnattended() throws Exception {
         "Skipping unattended test in CI: run locally for correctness");
 
     TestApp testApp = launchTestApp("resources.Main");
-    File traceFile = locateTrace("btrace/OnMethodTest.java");
+    try {
+      File traceFile = locateTrace("btrace/OnMethodTest.java");
 
-    String pid = String.valueOf(testApp.getPid());
-    AtomicBoolean hasError = new AtomicBoolean(false);
-    System.out.println("===> btrace -x (unattended)");
+      String pid = String.valueOf(testApp.getPid());
+      // Allow time for the worker thread to start after "ready:" is printed
+      try {
+        Thread.sleep(500L);
+      } catch (InterruptedException ie) {
+        Thread.currentThread().interrupt();
+      }
+      AtomicBoolean hasError = new AtomicBoolean(false);
+      AtomicBoolean probeStarted = new AtomicBoolean(false);
+      System.out.println("===> btrace -x (unattended)");
     runBTrace(
         new String[] {"-x", pid, traceFile.toString()},
         new ProcessOutputProcessor() {
           @Override
           public boolean onStdout(int lineno, String line) {
             System.out.println("[btrace #" + lineno + "] " + line);
+            if (line.contains("BTrace Probe:") || line.contains("Successfully started")) {
+              probeStarted.set(true);
+            }
             return lineno < 500;
           }
 
           @Override
           public boolean onStderr(int lineno, String line) {
-            System.err.println("[btrace #" + lineno + "] " + line);
+            System.err.println("[btrace err] " + line);
             hasError.set(true);
             return lineno < 10;
           }
         });
 
     assertFalse(hasError.get(), "btrace -x reported errors");
+    System.out.println("===> probe started: " + probeStarted.get());
 
     // Poll list of probes to discover the probe id reliably
     System.out.println("===> polling btrace -lp for probe id");
@@ -512,10 +524,13 @@ public boolean onStderr(int lineno, String line) {
       }
     }
 
-    // Assert exactly one matching probe is present
-    org.junit.jupiter.api.Assertions.assertEquals(1, matchCount[0],
-        "expected exactly one OnMethodTest probe listed by -lp");
-    assertNotNull(probeId[0], "probe id not found in -lp within timeout");
+      // Assert exactly one matching probe is present
+      org.junit.jupiter.api.Assertions.assertEquals(1, matchCount[0],
+          "expected exactly one OnMethodTest probe listed by -lp");
+      assertNotNull(probeId[0], "probe id not found in -lp within timeout");
+    } finally {
+      testApp.stop();
+    }
   }
 
     @ParameterizedTest(name = "testThreadStart: dynamic={0}")

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

@@ -730,11 +730,13 @@ public void runBTrace(String[] args, ProcessOutputProcessor outputProcessor) thr
                 "-cp",
                 cp,
                 "org.openjdk.btrace.client.Main",
-                debugBTrace ? "-v" : "",
                 "-cp",
                 eventsClassPath,
                 "-d",
                 Paths.get(System.getProperty("java.io.tmpdir"), "btrace-test").toString()));
+    if (debugBTrace) {
+      argVals.add(4, "-v"); // insert after Main class name
+    }
     argVals.addAll(Arrays.asList(args));
     if (Files.exists(Paths.get(javaHome, "jmods"))) {
       argVals.addAll(
@@ -857,11 +859,13 @@ public Process runBTrace(
                 "-cp",
                 cp,
                 "org.openjdk.btrace.client.Main",
-                debugBTrace ? "-v" : "",
                 "-cp",
                 eventsClassPath,
                 "-d",
                 Paths.get(System.getProperty("java.io.tmpdir"), "btrace-test").toString()));
+    if (debugBTrace) {
+      argVals.add(4, "-v"); // insert after Main class name
+    }
     argVals.addAll(Arrays.asList(args));
     if (Files.exists(Paths.get(javaHome, "jmods"))) {
       argVals.addAll(