fix(coding-agent,mom): retry fs watchers on async errors closes #3564

packages/mom/test/events.test.ts

@@ -0,0 +1,50 @@
+import { existsSync, type FSWatcher, mkdtempSync, rmSync } from "node:fs";
+import { tmpdir } from "node:os";
+import { join } from "node:path";
+import { afterEach, beforeEach, describe, expect, it, vi } from "vitest";
+import { EventsWatcher } from "../src/events.js";
+import type { SlackBot, SlackEvent } from "../src/slack.js";
+
+describe("EventsWatcher fs.watch error handling", () => {
+	let tempDir: string;
+
+	beforeEach(() => {
+		tempDir = mkdtempSync(join(tmpdir(), "mom-events-"));
+	});
+
+	afterEach(() => {
+		if (tempDir && existsSync(tempDir)) {
+			rmSync(tempDir, { recursive: true, force: true });
+		}
+	});
+
+	it("retries the events fs watcher 5 seconds after an async error", async () => {
+		vi.useFakeTimers();
+		const slack = {
+			enqueueEvent: vi.fn((_event: SlackEvent) => true),
+		} as unknown as SlackBot;
+		const eventsDir = join(tempDir, "events");
+		const watcher = new EventsWatcher(eventsDir, slack);
+
+		try {
+			watcher.start();
+			const watcherWithInternals = watcher as unknown as { watcher: FSWatcher | null };
+			const originalWatcher = watcherWithInternals.watcher;
+			expect(originalWatcher).not.toBeNull();
+			expect(originalWatcher?.listenerCount("error")).toBeGreaterThan(0);
+
+			originalWatcher?.emit("error", new Error("simulated EMFILE"));
+			expect(watcherWithInternals.watcher).toBeNull();
+
+			await vi.advanceTimersByTimeAsync(4999);
+			expect(watcherWithInternals.watcher).toBeNull();
+
+			await vi.advanceTimersByTimeAsync(1);
+			expect(watcherWithInternals.watcher).not.toBeNull();
+			expect(watcherWithInternals.watcher).not.toBe(originalWatcher);
+		} finally {
+			watcher.stop();
+			vi.useRealTimers();
+		}
+	});
+});