fix(anime): guard playback races and harden install/extract tests

- Tag subtitle cache writes with a generation counter so overlapping playEpisode calls can't clobber the shared cache dir, and don't fail playback when track setup errors
- Ignore stale episode clicks in the detail panel via a LatestRequest guard on playback
- Extract a resetGrid helper in animeui to dedupe grid-clearing logic
- Assert reader cancellation and extracted-file writes actually happen in installer/subsync tests

src/animeui/detail-panel.ts

@@ -25,6 +25,7 @@ export function createDetailPanel({ api, setStatus }: DetailPanelOptions) {
   let selectedAnime: { url: string; title: string; sourceId: string } | null = null;
   let resultsScrollTop = 0;
   const requests = new LatestRequest();
+  const playbacks = new LatestRequest();
 
   function formatEpisodeIndex(episode: AnimeBrowserEpisode, fallbackIndex: number): string {
     const value = episode.number ?? fallbackIndex;
@@ -38,6 +39,9 @@ export function createDetailPanel({ api, setStatus }: DetailPanelOptions) {
     const anime = selectedAnime;
     if (!anime) return;
 
+    // Only the newest click owns the button states and the status line; an
+    // earlier episode resolving late must not overwrite them.
+    const playback = playbacks.begin();
     for (const other of episodes.querySelectorAll<HTMLButtonElement>('.cue')) {
       other.removeAttribute('data-state');
     }
@@ -55,6 +59,8 @@ export function createDetailPanel({ api, setStatus }: DetailPanelOptions) {
       }),
     );
 
+    if (!playbacks.isCurrent(playback)) return;
+
     if (!attempt.ok) {
       button.removeAttribute('data-state');
       setStatus(describe(attempt.error), 'error');
@@ -163,6 +169,7 @@ export function createDetailPanel({ api, setStatus }: DetailPanelOptions) {
 
   function close(): void {
     requests.cancel();
+    playbacks.cancel();
     detail.classList.add('hidden');
     results.classList.remove('hidden');
     results.scrollTop = resultsScrollTop;