diff --git a/src/container-runner.ts b/src/container-runner.ts
index 1dc607f..47a8387 100644
--- a/src/container-runner.ts
+++ b/src/container-runner.ts
@@ -191,8 +191,17 @@ function buildVolumeMounts(
     group.folder,
     'agent-runner-src',
   );
-  if (!fs.existsSync(groupAgentRunnerDir) && fs.existsSync(agentRunnerSrc)) {
-    fs.cpSync(agentRunnerSrc, groupAgentRunnerDir, { recursive: true });
+  if (fs.existsSync(agentRunnerSrc)) {
+    const srcIndex = path.join(agentRunnerSrc, 'index.ts');
+    const cachedIndex = path.join(groupAgentRunnerDir, 'index.ts');
+    const needsCopy =
+      !fs.existsSync(groupAgentRunnerDir) ||
+      !fs.existsSync(cachedIndex) ||
+      (fs.existsSync(srcIndex) &&
+        fs.statSync(srcIndex).mtimeMs > fs.statSync(cachedIndex).mtimeMs);
+    if (needsCopy) {
+      fs.cpSync(agentRunnerSrc, groupAgentRunnerDir, { recursive: true });
+    }
   }
   mounts.push({
     hostPath: groupAgentRunnerDir,