Fix JENKINS-76241: Prevent POST race condition

core/src/main/resources/lib/layout/layout.jelly

@@ -123,6 +123,12 @@ THE SOFTWARE.
     <link rel="apple-touch-icon" href="${resURL}/apple-touch-icon.png" sizes="180x180" />
     <link rel="mask-icon" href="${resURL}/mask-icon.svg" color="#191717" />
 
+    <!-- CSRF Crumb meta tags for JavaScript access - Fix for JENKINS-76241 -->
+    <j:if test="${h.getCrumbRequestField() != null}">
+      <meta name="jenkins-crumb-field" content="${h.getCrumbRequestField()}" />
+      <meta name="jenkins-crumb-value" content="${h.getCrumb(request2)}" />
+    </j:if>
+
     <script src="${resURL}/scripts/behavior.js" type="text/javascript"/>
 
     <st:adjunct includes="org.kohsuke.stapler.bind"/>

war/src/main/webapp/css/responsive-grid.css

@@ -1815,4 +1815,4 @@
 }
 @-ms-viewport {
   width: device-width;
-}
+}

war/src/main/webapp/scripts/hudson-behavior.js

@@ -2709,3 +2709,60 @@ var layoutUpdateCallback = {
     }
   },
 };
+
+/**
+ * Fix for JENKINS-76241: Prevent POST race condition
+ * Apply Behaviour rules early - MINIMAL, SAFE VERSION
+ */
+(function () {
+  "use strict";
+
+  if (window._jenkinsPostHandlerFixApplied) {
+    return;
+  }
+  window._jenkinsPostHandlerFixApplied = true;
+
+  // Just apply Behaviour earlier - THAT'S IT
+  function applyEarly() {
+    if (typeof Behaviour !== "undefined" && Behaviour.apply) {
+      try {
+        Behaviour.apply();
+      } catch (e) {
+        // Ignore - will retry on DOMContentLoaded
+      }
+    }
+  }
+
+  // Apply immediately
+  applyEarly();
+
+  // Apply on DOMContentLoaded as backup
+  document.addEventListener("DOMContentLoaded", applyEarly);
+
+  // Watch for new content
+  if (typeof MutationObserver !== "undefined") {
+    var observer = new MutationObserver(function (mutations) {
+      var needsReapply = false;
+      mutations.forEach(function (mutation) {
+        mutation.addedNodes.forEach(function (node) {
+          if (
+            node.nodeType === 1 &&
+            (node.tagName === "FORM" ||
+              (node.querySelector && node.querySelector("FORM")))
+          ) {
+            needsReapply = true;
+          }
+        });
+      });
+      if (needsReapply) {
+        applyEarly();
+      }
+    });
+
+    document.addEventListener("DOMContentLoaded", function () {
+      if (document.body) {
+        observer.observe(document.body, { childList: true, subtree: true });
+      }
+    });
+  }
+})();