diff --git a/batch-publish/build.gradle b/batch-publish/build.gradle
index 2355212..1967e94 100644
--- a/batch-publish/build.gradle
+++ b/batch-publish/build.gradle
@@ -39,7 +39,7 @@ dependencies {
     implementation 'io.nats:jnats:2.26.3-SNAPSHOT'
     implementation 'org.jspecify:jspecify:1.0.0'
 
-    testImplementation 'io.nats:jnats-server-runner:3.1.1'
+    testImplementation 'io.nats:jnats-server-runner:4.0.2'
     testImplementation 'com.github.stefanbirkner:system-lambda:1.2.1'
     testImplementation 'nl.jqno.equalsverifier:equalsverifier:4.2.3'
 
diff --git a/chaos-runner/build.gradle b/chaos-runner/build.gradle
index 438c58e..51979bb 100644
--- a/chaos-runner/build.gradle
+++ b/chaos-runner/build.gradle
@@ -41,7 +41,7 @@ repositories {
 }
 
 dependencies {
-    implementation 'io.nats:jnats-server-runner:3.1.1'
+    implementation 'io.nats:jnats-server-runner:4.0.2'
 
     // this is only for the example and the uber jar won't include it
     implementation 'io.nats:jnats:2.26.2'
diff --git a/chaos-runner/src/main/java/io/synadia/chaos/ChaosRunner.java b/chaos-runner/src/main/java/io/synadia/chaos/ChaosRunner.java
index 8cc1a35..844caea 100644
--- a/chaos-runner/src/main/java/io/synadia/chaos/ChaosRunner.java
+++ b/chaos-runner/src/main/java/io/synadia/chaos/ChaosRunner.java
@@ -6,6 +6,7 @@
 import io.nats.ClusterDefaults;
 import io.nats.ClusterInsert;
 import io.nats.ClusterNode;
+import io.nats.JsConfig;
 import io.nats.NatsRunnerUtils;
 import io.nats.NatsServerRunner;
 
@@ -93,11 +94,10 @@ private NatsServerRunner createRunner(int index) throws Exception {
         ClusterInsert ci = clusterInserts.get(index);
         NatsServerRunner.Builder b = NatsServerRunner.builder()
             .debug(false)
-            .jetstream(true)
+            .jetstream(js)
             .configInserts(ci.configInserts)
             .port(ci.node.port)
-            .skipConnectValidate()
-            ;
+            .skipConnectValidate();
         return b.build();
     }
 
@@ -110,11 +110,19 @@ private void scheduleUp() {
     }
 
     private void downTask() {
+        // natsServerRunners is an ArrayList and shutdownServers() iterates it under this
+        // lock. executor.shutdown() does not interrupt a task already running, so without
+        // the lock a structural change here can race that iteration.
+        INSTANCE_LOCK.lock();
         try {
+            if (INSTANCE == null) {
+                // shut down before this task got to run
+                return;
+            }
             if (specificPort != -1) {
                 for (int i = 0; i < natsServerRunners.size(); i++) {
                     NatsServerRunner nsr = natsServerRunners.get(i);
-                    if (nsr.getPort() == specificPort) {
+                    if (nsr.getNatsPort() == specificPort) {
                         downIx = i;
                         break;
                     }
@@ -125,22 +133,39 @@ else if (random) {
             }
 
             NatsServerRunner runner = natsServerRunners.remove(downIx);
-            printer.out(CR_LABEL, "DOWN", runner.getPort());
+            printer.out(CR_LABEL, "DOWN", runner.getNatsPort());
             clusterInserts.add(clusterInserts.remove(downIx));
             runner.close();
             scheduleUp();
         }
         catch (Throwable e) {
-                printer.out(CR_LABEL, "DOWN/EX", e);
+            printer.out(CR_LABEL, "DOWN/EX", e);
+        }
+        finally {
+            INSTANCE_LOCK.unlock();
         }
     }
 
     private void upTask() {
         try {
             NatsServerRunner runner = createRunner(servers - 1);
-                printer.out(CR_LABEL, "UP", runner.getPort());
-            natsServerRunners.add(runner);
-            scheduleDown(delay);
+            INSTANCE_LOCK.lock();
+            try {
+                if (INSTANCE == null) {
+                    // Shut down while this server was starting. executor.shutdown() does not
+                    // interrupt a task already running, so we got here after shutdownServers()
+                    // had already closed out the list and the jvm hook was removed. Close it
+                    // here, or it outlives the jvm still holding its port.
+                    try { runner.close(); } catch (Exception ignore) {}
+                    return;
+                }
+                printer.out(CR_LABEL, "UP", runner.getNatsPort());
+                natsServerRunners.add(runner);
+                scheduleDown(delay);
+            }
+            finally {
+                INSTANCE_LOCK.unlock();
+            }
         }
         catch (Throwable e) {
                 printer.out(CR_LABEL, "UP/EX: ", e);
@@ -148,7 +173,7 @@ private void upTask() {
         }
     }
 
-    private static void deleteDirContents(Path dir, boolean alsoDeleteSelf) throws IOException {
+    private static void deleteDirContents(Path dir, boolean alsoDeleteSelf) {
         File fDir = dir.toFile();
         if (fDir.exists()) {
             File[] items = fDir.listFiles();
@@ -208,9 +233,10 @@ else if (!a.workDirectory.toFile().exists()) {
                 throw new IllegalArgumentException("Invalid specific port");
             }
             List<String> inserts = new ArrayList<>();
-            ClusterNode cn;
-            Path jsStorePath = Paths.get(jsStoreDirBase.toString(), "" + port);
-            cn = ClusterNode.builder()
+            // jsStoreDirBase is only set when js is on, and ClusterNode takes a null
+            // jsStoreDir, which is what the cluster branch ends up with in that case too
+            Path jsStorePath = js ? Paths.get(jsStoreDirBase.toString(), "" + port) : null;
+            ClusterNode cn = ClusterNode.builder()
                 .port(port)
                 .listen(listen)
                 .monitor(monitor < 1 ? null : monitor)
@@ -221,16 +247,9 @@ else if (!a.workDirectory.toFile().exists()) {
                 inserts.add("http: " + monitor);
             }
             if (js) {
-                String storeDir = jsStorePath.toString();
-                if (File.separatorChar == '\\') {
-                    storeDir = storeDir.replace("\\", "\\\\").replace("/", "\\\\");
-                }
-                else {
-                    storeDir = storeDir.replace("\\", "/");
-                }
-                inserts.add("jetstream {");
-                inserts.add("    store_dir=" + storeDir);
-                inserts.add("}");
+                // as of jnats-server-runner 4.0.2 JsConfig cleans and escapes the dir it is
+                // given, the same as the cluster branch gets by way of createClusterInserts
+                inserts.addAll(new JsConfig(jsStorePath).configInserts);
             }
             inserts.add("server_name=" + serverNamePrefix);
 
@@ -266,7 +285,10 @@ else if (!a.workDirectory.toFile().exists()) {
         // delete jsStoreDirs for clean start
         if (js) {
             for (ClusterInsert ci : clusterInserts) {
-                deleteDirContents(ci.node.jsStoreDir, false);
+                // jsStoreDir is nullable on ClusterNode, so it might not have been given one
+                if (ci.node.jsStoreDir != null) {
+                    deleteDirContents(ci.node.jsStoreDir, false);
+                }
             }
         }
 
@@ -307,12 +329,13 @@ public static ChaosRunner start(ChaosArguments a, ChaosPrinter printer) throws E
             }
 
             INSTANCE = new ChaosRunner(a, finalPrinter);
+            INSTANCE_ARGUMENTS = a;
 
             APP_SHUTDOWN_HOOK_THREAD = new Thread("app-shutdown-hook") {
                 @Override
                 public void run() {
-                    shutdownServers();
                     shutdownExecutor();
+                    shutdownServers();
                     finalPrinter.out(CR_LABEL, "EXIT");
                 }
             };
@@ -356,7 +379,11 @@ public static void shutdown() {
     public static void shutdownExecutor() {
         INSTANCE_LOCK.lock();
         try {
-            INSTANCE.executor.shutdown();
+            // guard matches shutdownServers(). This is public and is also reachable a
+            // second time when the jvm hook and an explicit shutdown() overlap.
+            if (INSTANCE != null) {
+                INSTANCE.executor.shutdown();
+            }
         }
         finally {
             INSTANCE_LOCK.unlock();
@@ -384,6 +411,7 @@ private static void shutdownServers() {
                     try { runner.close(); } catch (Exception ignore) {}
                 }
                 INSTANCE = null;
+                INSTANCE_ARGUMENTS = null;
             }
         }
         finally {
diff --git a/counters/build.gradle b/counters/build.gradle
index 2166dda..ca124e8 100644
--- a/counters/build.gradle
+++ b/counters/build.gradle
@@ -40,7 +40,7 @@ dependencies {
     implementation 'io.synadia:direct-batch:0.1.4'
     implementation 'org.jspecify:jspecify:1.0.0'
 
-    testImplementation 'io.nats:jnats-server-runner:3.1.1'
+    testImplementation 'io.nats:jnats-server-runner:4.0.2'
     testImplementation 'commons-codec:commons-codec:1.20.0'
     testImplementation 'com.github.stefanbirkner:system-lambda:1.2.1'
     testImplementation 'nl.jqno.equalsverifier:equalsverifier:4.2.3'
diff --git a/direct-batch/build.gradle b/direct-batch/build.gradle
index c350383..95b281a 100644
--- a/direct-batch/build.gradle
+++ b/direct-batch/build.gradle
@@ -44,7 +44,7 @@ dependencies {
     implementation 'io.nats:jnats:2.26.2'
     implementation 'org.jspecify:jspecify:1.0.0'
 
-    testImplementation 'io.nats:jnats-server-runner:3.1.1'
+    testImplementation 'io.nats:jnats-server-runner:4.0.2'
     testImplementation 'org.junit.jupiter:junit-jupiter:5.14.1'
     testImplementation 'org.junit.platform:junit-platform-launcher:1.14.3'
     testImplementation 'com.github.stefanbirkner:system-lambda:1.2.1'
diff --git a/encoded-kv/build.gradle b/encoded-kv/build.gradle
index d08683b..edab389 100644
--- a/encoded-kv/build.gradle
+++ b/encoded-kv/build.gradle
@@ -44,7 +44,7 @@ dependencies {
     implementation 'io.nats:jnats:2.26.2'
 
     testImplementation 'commons-codec:commons-codec:1.18.0'
-    testImplementation 'io.nats:jnats-server-runner:3.1.1'
+    testImplementation 'io.nats:jnats-server-runner:4.0.2'
     testImplementation 'org.junit.jupiter:junit-jupiter:5.14.1'
     testImplementation 'org.junit.platform:junit-platform-launcher:1.14.3'
     testImplementation 'com.github.stefanbirkner:system-lambda:1.2.1'
diff --git a/js-publish-extensions/build.gradle b/js-publish-extensions/build.gradle
index 18a1df2..c2182b1 100644
--- a/js-publish-extensions/build.gradle
+++ b/js-publish-extensions/build.gradle
@@ -51,7 +51,7 @@ dependencies {
     implementation 'io.nats:jnats:2.26.2'
     implementation 'io.synadia:retrier:0.2.1'
 
-    testImplementation 'io.nats:jnats-server-runner:3.1.1'
+    testImplementation 'io.nats:jnats-server-runner:4.0.2'
     testImplementation 'org.junit.jupiter:junit-jupiter:5.14.1'
     testImplementation 'org.junit.platform:junit-platform-launcher:1.14.3'
     testImplementation 'com.github.stefanbirkner:system-lambda:1.2.1'
diff --git a/pcgroups-cli/build.gradle b/pcgroups-cli/build.gradle
index d92d1e1..17757c4 100644
--- a/pcgroups-cli/build.gradle
+++ b/pcgroups-cli/build.gradle
@@ -20,7 +20,7 @@ dependencies {
     implementation project(':') // ':' means root project which is 'pcgroups'
     implementation 'info.picocli:picocli:4.7.5'
 
-    testImplementation 'io.nats:jnats-server-runner:3.1.1'
+    testImplementation 'io.nats:jnats-server-runner:4.0.2'
     testImplementation 'org.junit.jupiter:junit-jupiter:5.14.1'
     testImplementation 'org.junit.platform:junit-platform-launcher:1.14.3'
 }
diff --git a/pcgroups-cli/gradle/wrapper/gradle-wrapper.jar b/pcgroups-cli/gradle/wrapper/gradle-wrapper.jar
deleted file mode 100644
index 8bdaf60..0000000
Binary files a/pcgroups-cli/gradle/wrapper/gradle-wrapper.jar and /dev/null differ
diff --git a/pcgroups-cli/gradle/wrapper/gradle-wrapper.properties b/pcgroups-cli/gradle/wrapper/gradle-wrapper.properties
deleted file mode 100644
index 2a84e18..0000000
--- a/pcgroups-cli/gradle/wrapper/gradle-wrapper.properties
+++ /dev/null
@@ -1,7 +0,0 @@
-distributionBase=GRADLE_USER_HOME
-distributionPath=wrapper/dists
-distributionUrl=https\://services.gradle.org/distributions/gradle-9.0.0-bin.zip
-networkTimeout=10000
-validateDistributionUrl=true
-zipStoreBase=GRADLE_USER_HOME
-zipStorePath=wrapper/dists
diff --git a/pcgroups/build.gradle b/pcgroups/build.gradle
index 979c336..976de84 100644
--- a/pcgroups/build.gradle
+++ b/pcgroups/build.gradle
@@ -35,7 +35,7 @@ dependencies {
     api 'io.nats:jnats:2.26.2'
     api 'org.jspecify:jspecify:1.0.0'
 
-    testImplementation 'io.nats:jnats-server-runner:3.1.1'
+    testImplementation 'io.nats:jnats-server-runner:4.0.2'
     testImplementation 'org.junit.jupiter:junit-jupiter:5.14.1'
     testImplementation 'org.junit.platform:junit-platform-launcher:1.14.3'
 }
diff --git a/request-many/build.gradle b/request-many/build.gradle
index 7ce6627..77d7bc4 100644
--- a/request-many/build.gradle
+++ b/request-many/build.gradle
@@ -43,7 +43,7 @@ repositories {
 dependencies {
     implementation 'io.nats:jnats:2.26.2'
 
-    testImplementation 'io.nats:jnats-server-runner:3.1.1'
+    testImplementation 'io.nats:jnats-server-runner:4.0.2'
     testImplementation 'org.junit.jupiter:junit-jupiter:5.14.1'
     testImplementation 'org.junit.platform:junit-platform-launcher:1.14.3'
     testImplementation 'com.github.stefanbirkner:system-lambda:1.2.1'
diff --git a/retrier/build.gradle b/retrier/build.gradle
index 006fd53..74284ad 100644
--- a/retrier/build.gradle
+++ b/retrier/build.gradle
@@ -43,7 +43,7 @@ repositories {
 dependencies {
     implementation 'io.nats:jnats:2.26.2'
 
-    testImplementation 'io.nats:jnats-server-runner:3.1.1'
+    testImplementation 'io.nats:jnats-server-runner:4.0.2'
     testImplementation 'org.junit.jupiter:junit-jupiter:5.14.1'
     testImplementation 'org.junit.platform:junit-platform-launcher:1.14.3'
     testImplementation 'com.github.stefanbirkner:system-lambda:1.2.1'
diff --git a/schedule-message/build.gradle b/schedule-message/build.gradle
index a5ae443..3a892ae 100644
--- a/schedule-message/build.gradle
+++ b/schedule-message/build.gradle
@@ -41,7 +41,7 @@ dependencies {
     implementation 'org.jspecify:jspecify:1.0.0'
     implementation 'io.synadia:counters:0.2.2'
 
-    testImplementation 'io.nats:jnats-server-runner:3.1.1'
+    testImplementation 'io.nats:jnats-server-runner:4.0.2'
     testImplementation 'org.junit.jupiter:junit-jupiter:5.14.1'
     testImplementation 'org.junit.platform:junit-platform-launcher:1.14.3'
 }