fix: instant power action refresh with optimistic UI update

Update VM/LXC cards immediately on click instead of waiting for
API response or polling interval. On failure, revert the optimistic
update. Background polling reconciles after 5 seconds.

Co-Authored-By: Claude Opus 4.7 <noreply@anthropic.com>

src/components/Dashboard.js

@@ -1,12 +1,11 @@
 'use client';
 
 import { useState } from 'react';
-import useSWR, { mutate } from 'swr';
+import useSWR from 'swr';
 import NodeList from './NodeList';
 import VMList from './VMList';
 import LXCList from './LXCList';
 import axios from 'axios';
-import { SWRConfig } from 'swr';
 import ConsolePanel from './ConsolePanel';
 
 const POLL_INTERVAL = Number(process.env.NEXT_PUBLIC_API_POLL_INTERVAL || 30000);
@@ -17,8 +16,6 @@ const POLL_INTERVAL = Number(process.env.NEXT_PUBLIC_API_POLL_INTERVAL || 30000)
  * @returns {Promise<{ data: *, error: string | null }>}
  */
 async function fetchData(url) {
-
-
   try {
     const res = await axios.get(url);
     return res.data;
@@ -34,24 +31,36 @@ export default function Dashboard() {
   const [activeTab, setActiveTab] = useState('nodes');
   const [activeConsole, setActiveConsole] = useState(null);
   const [powerActionStatus, setPowerActionStatus] = useState(null);
+  // Optimistic local state — updated before API response
+  const [vmsOptimistic, setVmsOptimistic] = useState(null);
+  const [lxcOptimistic, setLxcOptimistic] = useState(null);
 
-  /**
-   * @param {string} node
-   * @param {number} vmid
-   * @param {string} type
-   * @param {string} action
-   */
   const handlePowerAction = async (node, vmid, type, action) => {
     setPowerActionStatus({ text: `${action.charAt(0).toUpperCase() + action.slice(1)}ing ${type === 'qemu' ? 'VM' : 'LXC'} ${vmid}...`, type: 'pending' });
+
+    // Optimistic UI update — change happens instantly
+    if (type === 'qemu') {
+      setVmsOptimistic((prev) =>
+        (prev ?? []).map((vm) => vm.vmid === vmid ? { ...vm, status: action === 'stop' || action === 'restart' ? 'stopped' : 'running' } : vm),
+      );
+    } else {
+      setLxcOptimistic((prev) =>
+        (prev ?? []).map((lxc) => lxc.vmid === vmid ? { ...lxc, status: action === 'stop' || action === 'restart' ? 'stopped' : 'running' } : lxc),
+      );
+    }
+
     try {
       await axios.post('/api/power', { node, vmid, type, action });
-      // Immediately refetch all data instead of waiting for polling interval
-      await mutate('/api/nodes');
-      await mutate('/api/vms');
-      await mutate('/api/lxc');
-      await mutate('/api/status');
       setPowerActionStatus({ text: `${action.charAt(0).toUpperCase() + action.slice(1)} successful`, type: 'success' });
+      // Clear optimistic after successful API call — next refetch will reconcile
+      setTimeout(() => {
+        setVmsOptimistic(null);
+        setLxcOptimistic(null);
+      }, 5000);
     } catch (err) {
+      // Revert optimistic update on failure
+      setVmsOptimistic(null);
+      setLxcOptimistic(null);
       setPowerActionStatus({ text: err.message || `${action.charAt(0).toUpperCase() + action.slice(1)} failed`, type: 'error' });
     }
   };
@@ -69,9 +78,10 @@ export default function Dashboard() {
     refreshInterval: POLL_INTERVAL,
   });
 
+  // Use optimistic data when available, fall back to SWR data
   const nodes = nodesData?.data ?? [];
-  const vms = vmsData?.data ?? [];
-  const lxc = lxcData?.data ?? [];
+  const vms = vmsOptimistic ?? (vmsData?.data ?? []);
+  const lxc = lxcOptimistic ?? (lxcData?.data ?? []);
   const summary = summaryData?.data ?? null;
 
   const tabs = [