fix(cache): do not resurrect a key deleted during getOrSet (#2246)

fluxer_api/pkgs/cache/src/__tests__/CacheInvalidationRace.test.ts

@@ -0,0 +1,45 @@
+// SPDX-License-Identifier: AGPL-3.0-or-later
+
+import {InMemoryProvider} from '@pkgs/cache/src/providers/InMemoryProvider';
+import {describe, expect, it} from 'vitest';
+
+function deferred<T>(): {promise: Promise<T>; resolve: (value: T) => void} {
+	let resolve!: (value: T) => void;
+	const promise = new Promise<T>((r) => {
+		resolve = r;
+	});
+	return {promise, resolve};
+}
+
+describe('cache invalidation during an in-flight produce', () => {
+	it('does not resurrect a value deleted while the factory was running', async () => {
+		const cache = new InMemoryProvider();
+		const gate = deferred<string>();
+		const pending = cache.getOrSet('session', async () => await gate.promise, 30);
+		await cache.delete('session');
+		gate.resolve('revoked-session');
+		await expect(pending).resolves.toBe('revoked-session');
+		expect(await cache.get('session')).toBeNull();
+	});
+
+	it('still stores the value when no invalidation happens', async () => {
+		const cache = new InMemoryProvider();
+		const gate = deferred<string>();
+		const pending = cache.getOrSet('session', async () => await gate.promise, 30);
+		gate.resolve('live-session');
+		await pending;
+		expect(await cache.get('session')).toBe('live-session');
+	});
+
+	it('keeps a later produce cacheable after an earlier one was invalidated', async () => {
+		const cache = new InMemoryProvider();
+		const first = deferred<string>();
+		const pending = cache.getOrSet('session', async () => await first.promise, 30);
+		await cache.delete('session');
+		first.resolve('stale');
+		await pending;
+		expect(await cache.get('session')).toBeNull();
+		await cache.getOrSet('session', async () => 'fresh', 30);
+		expect(await cache.get('session')).toBe('fresh');
+	});
+});