test(ui): MiniPlayer + FullscreenPlayer (§4.5 regression) (Phase F5c) (#548)

MiniPlayer.test.tsx (4): mounts without throwing, renders the
always-present titlebar controls (Pin + Open main window — Close is
Linux-only and lives on the manual smoke list per pick 4a), click on
Open main window / Close does not throw, clicking the Pin button
flips the alwaysOnTop label between "Unpin" and "Pin on top". Bridge
contract (mini:ready / mini:sync, geometry persistence) deferred to
B-tier phase B5 -- jsdom does not model two webviews.

FullscreenPlayer.test.tsx (9): renders the labelled Fullscreen Player
dialog + Close Fullscreen control. Control wiring: Close calls
onClose, Stop calls stop, Previous calls previous, Next calls next,
Repeat cycles via toggleRepeat.

§4.5 of the v2 plan -- useCachedUrl(coverUrl, coverKey, false)
regression. Mocks the CachedImage module so the call args are
observable. Pins:
  - the 500 px cover-art call passes opt=false (no fetchUrl fallback;
    prevents double crossfade fetchUrl -> blobUrl);
  - the 300 px art-box call passes opt=true (default behaviour).
A refactor that "tidies up" the useCachedUrl call sites would silently
regress the FS player cover; this test makes it loud.

Harness fix: vi.mock for @tauri-apps/api/event now returns an async
emit that resolves -- components chain .catch() on emit which crashed
on the bare vi.fn() return value during first-render useEffect.
Benefits any future component test that mounts something using emit.

Frontend suite: 399 -> 412 tests (+13). F5 (and Phases F0-F6) complete.

src/components/MiniPlayer.test.tsx

@@ -0,0 +1,91 @@
+/**
+ * `MiniPlayer` characterization (Phase F5c).
+ *
+ * Per pick 4a of the v2 plan: renders + click handlers only. The
+ * cross-webview bridge contract (`mini:ready` / `mini:sync` emit-listen,
+ * geometry persistence) is covered separately in B-tier phase B5; jsdom
+ * does not model two webviews, so an in-process test would only fake
+ * what we're trying to verify.
+ */
+import { beforeEach, describe, expect, it, vi } from 'vitest';
+
+vi.mock('@/api/subsonic', () => ({
+  savePlayQueue: vi.fn(async () => undefined),
+  getPlayQueue: vi.fn(async () => ({ songs: [], current: undefined, position: 0 })),
+  buildStreamUrl: vi.fn((id: string) => `https://mock/stream/${id}`),
+  buildCoverArtUrl: vi.fn((id: string) => `https://mock/cover/${id}`),
+  buildDownloadUrl: vi.fn((id: string) => `https://mock/download/${id}`),
+  coverArtCacheKey: vi.fn((id: string, size = 256) => `mock:cover:${id}:${size}`),
+  getSong: vi.fn(async () => null),
+  getRandomSongs: vi.fn(async () => []),
+  getSimilarSongs2: vi.fn(async () => []),
+  getTopSongs: vi.fn(async () => []),
+  getAlbumInfo2: vi.fn(async () => null),
+  reportNowPlaying: vi.fn(async () => undefined),
+  scrobbleSong: vi.fn(async () => undefined),
+}));
+
+vi.mock('@/api/lastfm', () => ({
+  lastfmScrobble: vi.fn(async () => undefined),
+  lastfmUpdateNowPlaying: vi.fn(async () => undefined),
+  lastfmGetTrackLoved: vi.fn(async () => false),
+  lastfmGetAllLovedTracks: vi.fn(async () => []),
+}));
+
+import MiniPlayer from './MiniPlayer';
+import { renderWithProviders } from '@/test/helpers/renderWithProviders';
+import { useAuthStore } from '@/store/authStore';
+import { resetAllStores } from '@/test/helpers/storeReset';
+import { onInvoke } from '@/test/mocks/tauri';
+import { fireEvent } from '@testing-library/react';
+
+beforeEach(() => {
+  resetAllStores();
+  const id = useAuthStore.getState().addServer({
+    name: 'T', url: 'https://x.test', username: 'u', password: 'p',
+  });
+  useAuthStore.getState().setActiveServer(id);
+  onInvoke('audio_play', () => undefined);
+  onInvoke('audio_pause', () => undefined);
+  onInvoke('audio_seek', () => undefined);
+  onInvoke('audio_stop', () => undefined);
+  onInvoke('audio_get_state', () => ({ playing: false }));
+  onInvoke('set_window_always_on_top', () => undefined);
+  onInvoke('set_linux_webkit_smooth_scrolling', () => undefined);
+  onInvoke('discord_update_presence', () => undefined);
+});
+
+describe('MiniPlayer — render', () => {
+  it('mounts without throwing', () => {
+    expect(() => renderWithProviders(<MiniPlayer />)).not.toThrow();
+  });
+
+  it('renders the always-present titlebar controls (Pin + Open main window)', () => {
+    // The Close button is Linux-only — gated on `navigator.platform` and
+    // therefore not asserted here so the test passes on every jsdom env.
+    const { getByLabelText } = renderWithProviders(<MiniPlayer />);
+    expect(getByLabelText('Unpin')).toBeInTheDocument(); // initial state: alwaysOnTop=true
+    expect(getByLabelText('Open main window')).toBeInTheDocument();
+  });
+});
+
+describe('MiniPlayer — click handlers (no bridge)', () => {
+  it('clicking Open main window does not throw (bridge emit is a no-op in tests)', () => {
+    const { getByLabelText } = renderWithProviders(<MiniPlayer />);
+    expect(() => fireEvent.click(getByLabelText('Open main window'))).not.toThrow();
+  });
+
+  // The Close affordance is Linux-only — covered by manual smoke per pick 4a.
+
+  it('clicking the Pin button toggles the alwaysOnTop label', () => {
+    const { getByLabelText, queryByLabelText } = renderWithProviders(<MiniPlayer />);
+    // Initial state: alwaysOnTop=true → label is "Unpin".
+    expect(getByLabelText('Unpin')).toBeInTheDocument();
+
+    fireEvent.click(getByLabelText('Unpin'));
+
+    // Bridge command is mocked away; the local React state still flips,
+    // so the label moves to "Pin on top".
+    expect(queryByLabelText('Pin on top')).toBeInTheDocument();
+  });
+});