download job: use the panel's exact url list (no server re-expansion)

A YouTube Mix/radio playlist (list=RD…) returns a different set of items on every
/api/playlist call (observed 779 / 1485 / 529 for the same URL). The job used to
re-expand the playlist server-side, so it would download a different list than the
count shown on the decision screen.

The panel now passes the already-expanded `urls[]` into the job, and the executor
uses them verbatim (falling back to expanding `url` only when no list is given).
The job downloads exactly what you decided on. Endpoint takes `urls[]` (stored as
inputs.urls) or `url`.

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

src/servers/api/tasks/pipeline-jobs-routes.ts

@@ -72,21 +72,26 @@ pipelineJobsRouter.post('/', async (c) => {
 });
 
 // POST /download — enqueue a video/audio download job (ReClip). Runs in its own lane, needs no capability
-// task. Body: { url (video or playlist), format:'audio'|'video', dir (target folder, home-relative),
-// root?, label? }. The job expands + fetches metadata (phase 1) then downloads survivors (phase 2).
+// task. Body: { urls[] (the exact list to download — preferred), OR url (expanded server-side),
+// format:'audio'|'video', dir (target folder, home-relative), root?, label? }. Passing `urls` locks the
+// job to the list the panel already expanded, so a Mix/radio playlist can't drift between fetch + job.
 pipelineJobsRouter.post('/download', async (c) => {
   const user = c.get('user');
   const body = await c.req.json<{
-    url: string;
+    url?: string;
+    urls?: string[];
     format?: 'audio' | 'video';
     dir?: string;
     root?: string;
     label?: string;
   }>();
-  if (!body.url) throw errors.BAD_REQUEST('url is required');
+  if (!body.url && !body.urls?.length) throw errors.BAD_REQUEST('url or urls is required');
   const rootDir = getRootDir(user, body.root);
   const absDir = resolveUserPath(rootDir, body.dir ?? '/'); // traversal-guarded
   const format = body.format === 'video' ? 'video' : 'audio';
+  const inputs: Record<string, string> = body.urls?.length
+    ? { urls: JSON.stringify(body.urls), format, absDir }
+    : { url: body.url!, format, absDir };
   const { jobId, status } = await jobManager.enqueueJob(
     {
       userId: user.id,
@@ -95,7 +100,7 @@ pipelineJobsRouter.post('/download', async (c) => {
       mode: 'download',
       taskDirName: 'video-download',
       taskName: body.label || (format === 'audio' ? 'Audio download' : 'Video download'),
-      inputs: { url: body.url, format, absDir },
+      inputs,
       cwd: body.dir ?? '/',
       config: {},
     },