perf: batch-load app history to eliminate N+1 fetches on board load

Previously each AppWidget fetched /api/apps/{id}/history individually
on mount, causing N sequential HTTP requests. Now the board page
server load fetches all app histories in a single Prisma query via
getBatchStatusHistory() and passes them to AppWidget via Svelte
context. AppWidget uses the pre-loaded data immediately with a
fallback fetch for non-board contexts.

src/lib/components/widget/AppWidget.svelte

@@ -1,5 +1,5 @@
 <script lang="ts">
-	import { onMount } from 'svelte';
+	import { onMount, getContext } from 'svelte';
 	import AppHealthBadge from '$lib/components/app/AppHealthBadge.svelte';
 	import AnimatedStatusRing from '$lib/components/app/AnimatedStatusRing.svelte';
 	import SparklineChart from '$lib/components/app/SparklineChart.svelte';
@@ -48,9 +48,13 @@
 
 	const cardStyleClass = $derived(`card-${theme.cardStyle}`);
 
-	let historyData: StatusPoint[] = $state([]);
-	let uptimePercent: number | null = $state(null);
-	let historyLoading = $state(true);
+	// Use pre-loaded history from context (set by board page) to avoid N+1 fetches
+	const appHistories = getContext<Record<string, { history: StatusPoint[]; uptimePercent: number }> | undefined>('appHistories');
+	const preloaded = appHistories?.[app.id];
+
+	let historyData: StatusPoint[] = $state(preloaded?.history ?? []);
+	let uptimePercent: number | null = $state(preloaded?.uptimePercent ?? null);
+	let historyLoading = $state(!preloaded);
 	let linksExpanded = $state(false);
 	let showContextMenu = $state(false);
 	let contextMenuPos = $state({ x: 0, y: 0 });
@@ -74,7 +78,9 @@
 		}
 	});
 
+	// Fallback: fetch history only if not pre-loaded via context
 	onMount(async () => {
+		if (preloaded) return;
 		try {
 			const res = await fetch(`/api/apps/${app.id}/history`);
 			if (res.ok) {

src/lib/server/services/appService.ts

@@ -127,6 +127,38 @@ export async function getStatusHistory(appId: string, limit: number = 50) {
 	});
 }
 
+/**
+ * Batch-fetch status history for multiple apps in a single query.
+ * Returns a map of appId -> { history, uptimePercent }.
+ */
+export async function getBatchStatusHistory(
+	appIds: readonly string[],
+	limitPerApp: number = 288
+): Promise<ReadonlyMap<string, { readonly history: readonly { status: string; responseTime: number | null; checkedAt: Date }[]; readonly uptimePercent: number }>> {
+	if (appIds.length === 0) return new Map();
+
+	const allStatuses = await prisma.appStatus.findMany({
+		where: { appId: { in: [...appIds] } },
+		orderBy: { checkedAt: 'desc' },
+		select: { appId: true, status: true, responseTime: true, checkedAt: true }
+	});
+
+	const result = new Map<string, { history: { status: string; responseTime: number | null; checkedAt: Date }[]; uptimePercent: number }>();
+
+	for (const appId of appIds) {
+		const statuses = allStatuses.filter((s) => s.appId === appId).slice(0, limitPerApp).reverse();
+		const totalChecks = statuses.length;
+		const onlineChecks = statuses.filter((s) => s.status === 'online').length;
+		const uptimePercent = totalChecks > 0 ? Math.round((onlineChecks / totalChecks) * 1000) / 10 : 0;
+		result.set(appId, {
+			history: statuses.map((s) => ({ status: s.status, responseTime: s.responseTime, checkedAt: s.checkedAt })),
+			uptimePercent
+		});
+	}
+
+	return result;
+}
+
 export async function getHealthcheckTargets() {
 	return prisma.app.findMany({
 		where: { healthcheckEnabled: true },

src/routes/boards/[boardId]/+page.server.ts

@@ -75,7 +75,26 @@ export const load: PageServerLoad = async ({ params, locals }) => {
 			}));
 		}
 
-		return { board, canEdit, allApps, users, groups };
+		// Batch-load sparkline history for all apps on this board (single query)
+		const appIdsOnBoard = board.sections
+			.flatMap((s: { widgets: { appId: string | null }[] }) => s.widgets)
+			.map((w: { appId: string | null }) => w.appId)
+			.filter((id: string | null): id is string => id !== null);
+
+		const historyMap = appIdsOnBoard.length > 0
+			? await appService.getBatchStatusHistory(appIdsOnBoard)
+			: new Map();
+
+		// Serialize the Map to a plain object for the client
+		const appHistories: Record<string, { history: { status: string; responseTime: number | null; checkedAt: string }[]; uptimePercent: number }> = {};
+		for (const [appId, data] of historyMap) {
+			appHistories[appId] = {
+				history: data.history.map((h) => ({ ...h, checkedAt: h.checkedAt.toISOString() })),
+				uptimePercent: data.uptimePercent
+			};
+		}
+
+		return { board, canEdit, allApps, users, groups, appHistories };
 	} catch (err) {
 		const message = err instanceof Error ? err.message : 'Board not found';
 		if (message.includes('not found')) {

src/routes/boards/[boardId]/+page.svelte

@@ -9,11 +9,15 @@
 	import CustomCssInjector from '$lib/components/layout/CustomCssInjector.svelte';
 	import WallpaperBackground from '$lib/components/background/WallpaperBackground.svelte';
 	import { broadcastDataChange } from '$lib/utils/broadcastSync.js';
+	import { setContext } from 'svelte';
 
 	let { data }: { data: PageData } = $props();
 
 	const boardCardSize = $derived((data.board.cardSize as 'compact' | 'medium' | 'large') ?? 'medium');
 
+	// Provide pre-loaded app histories via context to avoid N+1 fetches in AppWidget
+	setContext('appHistories', data.appHistories ?? {});
+
 	let showShareDialog = $state(false);
 	let guestToggleError = $state('');