fix(youtube): prevent playlist URLs from stalling yt-dlp probes (#180)

src/core/services/youtube/ytdlp-single-video-args.test.ts

@@ -0,0 +1,38 @@
+import assert from 'node:assert/strict';
+import test from 'node:test';
+import { buildYoutubeMetadataProbeArgs } from './metadata-probe';
+import { buildYoutubePlaybackResolveArgs } from './playback-resolve';
+import { buildDownloadArgs } from './track-download';
+import { buildYoutubeTrackProbeArgs } from './track-probe';
+import { YTDLP_SINGLE_VIDEO_ARG } from './ytdlp-command';
+
+// Regression guard for issue #179: a `list=`/`index=` URL made yt-dlp enumerate the whole
+// playlist (e.g. Watch Later) and blow past our 15s timeouts on every single-video call.
+const PLAYLIST_URL = 'https://www.youtube.com/watch?v=LKfWC6CgFng&list=WL&index=3';
+
+const cases: Array<{ name: string; args: string[] }> = [
+  { name: 'track probe', args: buildYoutubeTrackProbeArgs(PLAYLIST_URL) },
+  { name: 'metadata probe', args: buildYoutubeMetadataProbeArgs(PLAYLIST_URL) },
+  { name: 'playback resolve', args: buildYoutubePlaybackResolveArgs(PLAYLIST_URL, 'b') },
+  {
+    name: 'subtitle download',
+    args: buildDownloadArgs({
+      targetUrl: PLAYLIST_URL,
+      outputTemplate: '/tmp/out.%(ext)s',
+      sourceLanguages: ['ja'],
+      includeAutoSubs: true,
+      includeManualSubs: false,
+    }),
+  },
+];
+
+test('YTDLP_SINGLE_VIDEO_ARG is the yt-dlp flag that disables playlist expansion', () => {
+  assert.equal(YTDLP_SINGLE_VIDEO_ARG, '--no-playlist');
+});
+
+for (const { name, args } of cases) {
+  test(`${name} passes --no-playlist for playlist-scoped URLs`, () => {
+    assert.ok(args.includes('--no-playlist'), `${name} args: ${args.join(' ')}`);
+    assert.equal(args.at(-1), PLAYLIST_URL);
+  });
+}