perf: frontend request cache, poll pause, and code-split shell (#1052)

Host/status caching, shell code-split, SSH pool waits, host-metrics concurrency, background-tab idle, per-host status subscriptions, homepage poll quieting, and virtualized host sidebar + file manager lists.

src/ui/dashboard/DashboardTab.tsx

@@ -801,6 +801,7 @@ function CardItem({
   onAddServiceLink,
   onDeleteServiceLink,
   statusLoading,
+  isVisible = true,
 }: {
   slot: CardSlot;
   editMode: boolean;
@@ -830,6 +831,7 @@ function CardItem({
   onAddServiceLink: (label: string, url: string) => Promise<void>;
   onDeleteServiceLink: (id: number) => Promise<void>;
   statusLoading?: boolean;
+  isVisible?: boolean;
 }) {
   const cardRef = useRef<HTMLDivElement | null>(null);
 
@@ -926,6 +928,7 @@ function CardItem({
         {slot.id === "network_graph" && (
           <NetworkGraphCard
             embedded={true}
+            isVisible={isVisible}
             onOpenInNewTab={() => onOpenSingletonTab("network_graph")}
           />
         )}
@@ -1055,6 +1058,7 @@ type PanelColumnProps = {
   onAddServiceLink: (label: string, url: string) => Promise<void>;
   onDeleteServiceLink: (id: number) => Promise<void>;
   statusLoading: boolean;
+  isVisible?: boolean;
 };
 
 function PanelColumn({
@@ -1086,6 +1090,7 @@ function PanelColumn({
   onAddServiceLink,
   onDeleteServiceLink,
   statusLoading,
+  isVisible = true,
 }: PanelColumnProps) {
   const { t } = useTranslation();
   const sorted = [...slots].sort((a, b) => a.order - b.order);
@@ -1142,6 +1147,7 @@ function PanelColumn({
             onAddServiceLink={onAddServiceLink}
             onDeleteServiceLink={onDeleteServiceLink}
             statusLoading={statusLoading}
+            isVisible={isVisible}
           />
         </div>
       ))}
@@ -1192,9 +1198,12 @@ function ColumnDivider({
 export function DashboardTab({
   onOpenSingletonTab,
   onOpenTab,
+  isVisible = true,
 }: {
   onOpenSingletonTab: (type: TabType, pendingEvent?: string) => void;
   onOpenTab: (host: Host, type: TabType) => void;
+  /** When false, pause dashboard metrics refresh while the tab stays mounted. */
+  isVisible?: boolean;
 }) {
   const { t, i18n } = useTranslation();
   const { initialLoadComplete } = useServerStatus();
@@ -1349,7 +1358,9 @@ export function DashboardTab({
       const mapped = raw.map(sshHostToHost);
       const statusHosts = mapped.filter(isStatusCheckEnabled);
       if (mounted) setHosts(mapped);
-      fetchMetrics(statusHosts).catch(() => {});
+      if (isVisible) {
+        fetchMetrics(statusHosts).catch(() => {});
+      }
     };
     load();
 
@@ -1399,7 +1410,14 @@ export function DashboardTab({
       })
       .catch(() => {});
 
+    if (!isVisible) {
+      return () => {
+        mounted = false;
+      };
+    }
+
     const metricsInterval = setInterval(async () => {
+      if (document.visibilityState === "hidden") return;
       const raw = await getSSHHosts().catch(() => []);
       const mapped = raw.map(sshHostToHost);
       const statusHosts = mapped.filter(isStatusCheckEnabled);
@@ -1411,17 +1429,18 @@ export function DashboardTab({
       mounted = false;
       clearInterval(metricsInterval);
     };
-  }, [fetchMetrics]);
+  }, [fetchMetrics, isVisible]);
 
   useEffect(() => {
-    if (viewerSessionsRef.current.size === 0) return;
+    if (!isVisible || viewerSessionsRef.current.size === 0) return;
     const heartbeat = setInterval(async () => {
+      if (document.visibilityState === "hidden") return;
       for (const [, sessionId] of viewerSessionsRef.current) {
         sendMetricsHeartbeat(sessionId).catch(() => {});
       }
     }, 30000);
     return () => clearInterval(heartbeat);
-  }, [hostMetrics]);
+  }, [hostMetrics, isVisible]);
 
   const handleClearActivity = async () => {
     try {
@@ -1594,6 +1613,7 @@ export function DashboardTab({
     onAddServiceLink: handleAddServiceLink,
     onDeleteServiceLink: handleDeleteServiceLink,
     statusLoading,
+    isVisible,
   };
 
   const isMobile = useIsMobile();
@@ -1733,6 +1753,7 @@ export function DashboardTab({
               {slot.id === "network_graph" && (
                 <NetworkGraphCard
                   embedded={true}
+                  isVisible={isVisible}
                   onOpenInNewTab={() => onOpenSingletonTab("network_graph")}
                 />
               )}