diff --git a/lib/Controller/AssetController.php b/lib/Controller/AssetController.php
index 9a34362..ef1330b 100644
--- a/lib/Controller/AssetController.php
+++ b/lib/Controller/AssetController.php
@@ -27,29 +27,40 @@
  * the current user can read the underlying file before serving any bytes.
  */
 class AssetController extends Controller {
+	/** Mirrors `MIME_BY_EXTENSION` in `src/elpx/asset-map.ts` (parity-tested). */
 	private const MIME_MAP = [
 		'html' => 'text/html; charset=utf-8',
 		'htm' => 'text/html; charset=utf-8',
+		'xhtml' => 'application/xhtml+xml; charset=utf-8',
 		'css' => 'text/css; charset=utf-8',
 		'js' => 'text/javascript; charset=utf-8',
 		'mjs' => 'text/javascript; charset=utf-8',
 		'json' => 'application/json; charset=utf-8',
+		'xml' => 'application/xml; charset=utf-8',
+		'txt' => 'text/plain; charset=utf-8',
 		'svg' => 'image/svg+xml',
 		'png' => 'image/png',
 		'jpg' => 'image/jpeg',
 		'jpeg' => 'image/jpeg',
 		'gif' => 'image/gif',
 		'webp' => 'image/webp',
+		'ico' => 'image/x-icon',
 		'mp3' => 'audio/mpeg',
 		'mp4' => 'video/mp4',
+		'm4a' => 'audio/mp4',
+		'm4v' => 'video/mp4',
 		'ogg' => 'audio/ogg',
+		'oga' => 'audio/ogg',
+		'ogv' => 'video/ogg',
 		'wav' => 'audio/wav',
 		'webm' => 'video/webm',
 		'vtt' => 'text/vtt',
 		'woff' => 'font/woff',
 		'woff2' => 'font/woff2',
 		'ttf' => 'font/ttf',
+		'otf' => 'font/otf',
 		'eot' => 'application/vnd.ms-fontobject',
+		'pdf' => 'application/pdf',
 	];
 
 	public function __construct(
diff --git a/src/elpx/service-worker-client.ts b/src/elpx/service-worker-client.ts
index 01e1b2c..7e25b7e 100644
--- a/src/elpx/service-worker-client.ts
+++ b/src/elpx/service-worker-client.ts
@@ -63,7 +63,7 @@ async function registerRuntimeWorker(): Promise<RuntimeWorker> {
 
 /**
  * Resolves once the registered Service Worker reaches the `activated`
- * state. Resolves immediately when the worker is already controlling the
+ * state, and rejects if it becomes `redundant`. Resolves immediately when the worker is already controlling the
  * page; otherwise listens for `statechange` on the
  * installing/waiting/active worker.
  * @param registration Result of `navigator.serviceWorker.register`.
@@ -72,7 +72,7 @@ function waitForActive(registration: ServiceWorkerRegistration): Promise<void> {
 	if (registration.active && navigator.serviceWorker.controller) {
 		return Promise.resolve()
 	}
-	return new Promise((resolve) => {
+	return new Promise((resolve, reject) => {
 		const sw = registration.installing || registration.waiting || registration.active
 		if (!sw) {
 			resolve()
@@ -85,6 +85,10 @@ function waitForActive(registration: ServiceWorkerRegistration): Promise<void> {
 		sw.addEventListener('statechange', () => {
 			if (sw.state === 'activated') {
 				resolve()
+			} else if (sw.state === 'redundant') {
+				// Install failed or was superseded; without this the viewer
+				// would wait forever instead of using the server fallback.
+				reject(new Error('The eXeLearning Service Worker failed to activate.'))
 			}
 		})
 	})
diff --git a/src/viewer/ElpxViewer.vue b/src/viewer/ElpxViewer.vue
index 49f3aba..15939cb 100644
--- a/src/viewer/ElpxViewer.vue
+++ b/src/viewer/ElpxViewer.vue
@@ -133,6 +133,12 @@ export default defineComponent({
 				try {
 					const worker = await ensureRuntimeWorker()
 					await registerSession(worker, session)
+					if (this.$.isUnmounted) {
+						// Closed while loading: teardown already ran without
+						// this session, so release the bytes held by the SW.
+						void unregisterSession(worker, session.id)
+						return
+					}
 
 					this.session = session
 					this.worker = worker
diff --git a/tests/Unit/Controller/AssetControllerTest.php b/tests/Unit/Controller/AssetControllerTest.php
index 3c86195..269763c 100644
--- a/tests/Unit/Controller/AssetControllerTest.php
+++ b/tests/Unit/Controller/AssetControllerTest.php
@@ -137,6 +137,16 @@ public function testUsesOctetStreamForUnknownExtension(): void {
 		self::assertSame('application/octet-stream', $response->getHeaders()['Content-Type']);
 	}
 
+	public function testMimeMapMatchesTheServiceWorkerMap(): void {
+		$source = file_get_contents(__DIR__ . '/../../../src/elpx/asset-map.ts');
+		self::assertIsString($source);
+		preg_match_all("/^\t(\w+): '([^']+)',$/m", $source, $matches);
+		$tsMap = array_combine($matches[1], $matches[2]);
+
+		self::assertNotEmpty($tsMap);
+		self::assertSame($tsMap, (new \ReflectionClassConstant(AssetController::class, 'MIME_MAP'))->getValue());
+	}
+
 	private function authenticate(): IUser {
 		$user = $this->createMock(IUser::class);
 		$user->method('getUID')->willReturn('alice');
diff --git a/tests/js/service-worker-client.test.ts b/tests/js/service-worker-client.test.ts
new file mode 100644
index 0000000..ce43491
--- /dev/null
+++ b/tests/js/service-worker-client.test.ts
@@ -0,0 +1,49 @@
+import { afterEach, describe, expect, it, vi } from 'vitest'
+
+vi.mock('@nextcloud/router', () => ({ generateUrl: (path: string) => path }))
+
+/** Fake ServiceWorker whose state the test drives. */
+function fakeWorker(state: ServiceWorkerState) {
+	const worker = new EventTarget() as ServiceWorker & { state: ServiceWorkerState }
+	worker.state = state
+	return worker
+}
+
+async function loadClient(installing: ServiceWorker) {
+	vi.resetModules()
+	const registration = { installing, waiting: null, active: null }
+	vi.stubGlobal('navigator', {
+		serviceWorker: { controller: null, register: vi.fn().mockResolvedValue(registration) },
+	})
+	return import('../../src/elpx/service-worker-client')
+}
+
+describe('ensureRuntimeWorker', () => {
+	afterEach(() => {
+		vi.unstubAllGlobals()
+	})
+
+	it('resolves once the worker activates', async () => {
+		const worker = fakeWorker('installing')
+		const { ensureRuntimeWorker } = await loadClient(worker)
+
+		const pending = ensureRuntimeWorker()
+		await Promise.resolve()
+		worker.state = 'activated'
+		worker.dispatchEvent(new Event('statechange'))
+
+		await expect(pending).resolves.toMatchObject({ scope: '/apps/exelearning/runtime/' })
+	})
+
+	it('rejects when the worker becomes redundant so the viewer can fall back', async () => {
+		const worker = fakeWorker('installing')
+		const { ensureRuntimeWorker } = await loadClient(worker)
+
+		const pending = ensureRuntimeWorker()
+		await Promise.resolve()
+		worker.state = 'redundant'
+		worker.dispatchEvent(new Event('statechange'))
+
+		await expect(pending).rejects.toThrow('failed to activate')
+	})
+})