feat(torrents): support piece priority

src/utils/downloads.test.ts

@@ -8,6 +8,7 @@ import {
   canonicalizeDownloadFileName,
   isValidTorrentExcludeTrackerList,
   isValidTorrentTrackerList,
+  normalizeTorrentPrioritizePiece,
   redactDownloadForPersistence,
   resolveDownloadConnections
 } from './downloads';
@@ -77,6 +78,20 @@ describe('Torrent tracker input validation', () => {
   });
 });
 
+describe('Torrent piece priority validation', () => {
+  it('normalizes head and tail preview policies', () => {
+    expect(normalizeTorrentPrioritizePiece(' tail = 64k, HEAD ')).toBe('head,tail=64K');
+    expect(normalizeTorrentPrioritizePiece('head=1m,tail=1024M')).toBe('head=1M,tail=1024M');
+    expect(normalizeTorrentPrioritizePiece('')).toBeNull();
+  });
+
+  it('rejects duplicate, unsupported, malformed, and oversized policies', () => {
+    for (const value of ['head,head', 'middle', 'head=0K', 'tail=1G', 'head=1K,', 'head=1025M']) {
+      expect(normalizeTorrentPrioritizePiece(value)).toBeNull();
+    }
+  });
+});
+
 describe('download connection resolution', () => {
   it('uses a clamped fallback for legacy rows without a saved value', () => {
     expect(resolveDownloadConnections(undefined, 8)).toBe(8);