feat(pending-banner): add Discard button to cancel pending restart without applying

- DELETE /api/config/pending endpoint calls _clear_pending_restart()
- cellAPI.cancelPending() calls the new endpoint
- PendingRestartBanner shows a "Discard" button alongside "Apply Now";
  clicking it drops the pending state without restarting any containers

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

webui/src/App.jsx

@@ -35,9 +35,10 @@ import Vault from './pages/Vault';
 import ContainerDashboard from './components/ContainerDashboard';
 import CellNetwork from './pages/CellNetwork';
 
-function PendingRestartBanner({ pending, onApply }) {
+function PendingRestartBanner({ pending, onApply, onCancel }) {
   const [confirming, setConfirming] = useState(false);
   const [applying, setApplying] = useState(false);
+  const [cancelling, setCancelling] = useState(false);
 
   const handleApply = async () => {
     setApplying(true);
@@ -49,6 +50,15 @@ function PendingRestartBanner({ pending, onApply }) {
     }
   };
 
+  const handleCancel = async () => {
+    setCancelling(true);
+    try {
+      await onCancel();
+    } finally {
+      setCancelling(false);
+    }
+  };
+
   return (
     <>
       <div className="mb-6 bg-warning-50 border border-warning-300 rounded-lg p-4">
@@ -66,14 +76,23 @@ function PendingRestartBanner({ pending, onApply }) {
               )}
             </div>
           </div>
-          <button
-            onClick={() => setConfirming(true)}
-            disabled={applying}
-            className="ml-4 flex-shrink-0 flex items-center gap-1.5 px-3 py-1.5 bg-warning-600 hover:bg-warning-700 disabled:opacity-50 text-white text-sm font-medium rounded-md transition-colors"
-          >
-            <RefreshCw className={`h-4 w-4 ${applying ? 'animate-spin' : ''}`} />
-            {applying ? 'Restarting…' : 'Apply Now'}
-          </button>
+          <div className="ml-4 flex-shrink-0 flex items-center gap-2">
+            <button
+              onClick={handleCancel}
+              disabled={applying || cancelling}
+              className="flex items-center gap-1.5 px-3 py-1.5 bg-white hover:bg-gray-50 disabled:opacity-50 text-warning-700 text-sm font-medium rounded-md border border-warning-300 transition-colors"
+            >
+              {cancelling ? 'Discarding…' : 'Discard'}
+            </button>
+            <button
+              onClick={() => setConfirming(true)}
+              disabled={applying || cancelling}
+              className="flex items-center gap-1.5 px-3 py-1.5 bg-warning-600 hover:bg-warning-700 disabled:opacity-50 text-white text-sm font-medium rounded-md transition-colors"
+            >
+              <RefreshCw className={`h-4 w-4 ${applying ? 'animate-spin' : ''}`} />
+              {applying ? 'Restarting…' : 'Apply Now'}
+            </button>
+          </div>
         </div>
       </div>
 
@@ -147,7 +166,11 @@ function App() {
 
   const handleApply = useCallback(async () => {
     await cellAPI.applyPending();
-    // Optimistically clear the banner; containers are restarting
+    setPending({ needs_restart: false, changes: [] });
+  }, []);
+
+  const handleCancel = useCallback(async () => {
+    await cellAPI.cancelPending();
     setPending({ needs_restart: false, changes: [] });
   }, []);
 
@@ -209,7 +232,7 @@ function App() {
               )}
 
               {isOnline && pending.needs_restart && (
-                <PendingRestartBanner pending={pending} onApply={handleApply} />
+                <PendingRestartBanner pending={pending} onApply={handleApply} onCancel={handleCancel} />
               )}
 
               <Routes>

webui/src/services/api.js

@@ -44,6 +44,7 @@ export const cellAPI = {
   exportConfig: (format = 'json') => api.get('/api/config/export', { params: { format } }),
   importConfig: (config, format = 'json') => api.post('/api/config/import', { config, format }),
   getPending: () => api.get('/api/config/pending'),
+  cancelPending: () => api.delete('/api/config/pending'),
   applyPending: () => api.post('/api/config/apply'),
 };