perf(app): load embed author and footer icons through the image cache (#1756)

fluxer_app/src/features/messaging/hooks/useCachedImageLoaded.ts

@@ -0,0 +1,26 @@
+// SPDX-License-Identifier: AGPL-3.0-or-later
+
+import * as ImageCacheUtils from '@app/features/messaging/utils/ImageCacheUtils';
+import {useEffect, useState} from 'react';
+
+export function useCachedImageLoaded(src: string | null | undefined): boolean {
+	const resolved = src ?? null;
+	const [readySrc, setReadySrc] = useState<string | null>(() =>
+		resolved !== null && ImageCacheUtils.hasImage(resolved) ? resolved : null,
+	);
+	useEffect(() => {
+		if (resolved === null) {
+			return;
+		}
+		let active = true;
+		const markReady = (): void => {
+			if (active) setReadySrc(resolved);
+		};
+		const cleanup = ImageCacheUtils.loadImage(resolved, markReady, markReady);
+		return () => {
+			active = false;
+			cleanup();
+		};
+	}, [resolved]);
+	return resolved !== null && readySrc === resolved;
+}

fluxer_app/src/features/messaging/utils/ImageCacheUtils.test.ts

@@ -0,0 +1,32 @@
+// @vitest-environment happy-dom
+// SPDX-License-Identifier: AGPL-3.0-or-later
+
+import * as ImageCacheUtils from '@app/features/messaging/utils/ImageCacheUtils';
+import {afterEach, describe, expect, it, vi} from 'vitest';
+
+afterEach(() => {
+	ImageCacheUtils._clearForTests();
+});
+
+describe('loadImage rejection path', () => {
+	it('reports an unusable source through onError so callers can fall back', () => {
+		const onLoad = vi.fn();
+		const onError = vi.fn();
+		ImageCacheUtils.loadImage(null, onLoad, onError);
+		expect(onLoad).not.toHaveBeenCalled();
+		expect(onError).toHaveBeenCalledTimes(1);
+	});
+
+	it('reports an oversized source through onError rather than queueing it', () => {
+		const onLoad = vi.fn();
+		const onError = vi.fn();
+		ImageCacheUtils.loadImage(`https://cdn.test/${'a'.repeat(32 * 1024)}.png`, onLoad, onError);
+		expect(onLoad).not.toHaveBeenCalled();
+		expect(onError).toHaveBeenCalledTimes(1);
+	});
+
+	it('returns a no-op disposer when it rejects, so cleanup stays safe', () => {
+		const dispose = ImageCacheUtils.loadImage(null, vi.fn(), vi.fn());
+		expect(() => dispose()).not.toThrow();
+	});
+});