fix: clarify browser application guidance

test/apps/webapp/FSAPIStorageEventManagerAdapter.unit.spec.ts

@@ -0,0 +1,34 @@
+import { LOG_LEVEL_INFO } from "@vrtmrz/livesync-commonlib/compat/common/types";
+import type { IStorageEventWatchHandlers } from "@vrtmrz/livesync-commonlib/compat/managers/adapters";
+import { afterEach, describe, expect, it, vi } from "vitest";
+
+import { FSAPIStorageEventManagerAdapter } from "@/apps/webapp/managers/FSAPIStorageEventManagerAdapter";
+import type { FSAPIFile } from "@/apps/webapp/adapters/FSAPITypes";
+
+afterEach(() => {
+    vi.unstubAllGlobals();
+});
+
+describe("WebApp file watching guidance", () => {
+    it("offers a capability-based manual fallback when FileSystemObserver is unavailable", async () => {
+        vi.stubGlobal("FileSystemObserver", undefined);
+        const addLog = vi.fn();
+        const adapter = new FSAPIStorageEventManagerAdapter({} as FileSystemDirectoryHandle, addLog);
+        const handlers = {
+            onCreate: vi.fn(),
+            onChange: vi.fn(),
+            onDelete: vi.fn(),
+            onRename: vi.fn(),
+            onRaw: vi.fn(),
+        } satisfies IStorageEventWatchHandlers<FSAPIFile>;
+
+        await adapter.watch.beginWatch(handlers);
+
+        expect(addLog).toHaveBeenCalledWith(
+            "Use 'Scan local files' after external changes",
+            LOG_LEVEL_INFO,
+            "fsapi-watch"
+        );
+        expect(addLog.mock.calls.map(([message]) => String(message)).join("\n")).not.toMatch(/Chrome \d+/);
+    });
+});