feat(backend): Mittelweg cascade — never download wrong song on no duration match

When a track's duration is known but nothing matches the duration window, the
cascade no longer falls back to blind title-only/no-filter grabs (which pulled
same-titled videos by other uploaders, e.g. a "recognize" fan clip). Instead it
relaxes only the duration constraint while still REQUIRING the artist channel +
title. If nothing matches, the download produces no file and the job now fails
cleanly with "Nicht eindeutig gefunden — bitte Direktlink im Importer nutzen"
(previously it falsely reported success with no file).

Single, album and playlist paths all surface the not-found state.

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

backend/lib/downloader.js

@@ -33,7 +33,9 @@ async function downloadAlbumTracks({ jobId, artist, albumTitle, tracks, artworkU
         outputDir:   CONFIG.musicPath,
         durationMs:  track.trackTimeMillis || undefined,
       });
-      if (result?.skipped) skipped++; else done++;
+      if (result?.skipped) skipped++;
+      else if (result?.notFound) log(jobId, `⚠️  Nicht eindeutig gefunden: "${track.trackName || track.title}" — Direktlink nutzen`);
+      else done++;
       updateJob(jobId, { progress: Math.round(((done + skipped) / total) * 90) });
     } catch (e) {
       log(jobId, `⚠️  Fehler bei "${track.trackName || track.title}": ${e.message}`);

backend/lib/ytdlp.js

@@ -295,32 +295,19 @@ async function downloadTrack({ jobId, artist, rawArtist, albumArtist, title, alb
       // 4. YT top-10 — no channel check
       await spawnYtdlp([`ytsearch10:${query}`, ...PI_FILTERED_10, ...mf(dur, true), ...baseArgs]);
     }
+    // No duration match. "Mittelweg": relax the duration constraint but REQUIRE the artist
+    // channel (+ title). This catches legit tracks whose YT upload duration drifts from the
+    // iTunes value, while never grabbing a same-titled video by someone else. If nothing
+    // matches title+channel we download NOTHING and the job fails cleanly (see end of fn) —
+    // far better than silently saving the wrong song (e.g. a "recognize" fan clip).
     if (!hasAudio()) {
-      // 6. YTM all — no duration check
-      log(jobId, '⚠️  Kein Treffer im Dauerbereich — suche ohne Dauerbeschränkung…');
-      await tryYtm(0, mf(null, true));
+      // 5. YTM all — no duration, but channel + title required
+      log(jobId, '⚠️  Kein Treffer im Dauerbereich — suche ohne Dauer, aber mit Künstler-Channel…');
+      await tryYtm(0, mf(null, true, true));
     }
     if (!hasAudio()) {
-      // 7. YT top-5 — no duration check
-      await spawnYtdlp([`ytsearch5:${query}`, ...PI_FILTERED, ...mf(null, true), ...baseArgs]);
-    }
-    if (!hasAudio()) {
-      // 8. YTM all — title only (no variant filter)
-      log(jobId, '⚠️  Letzter gefilterter Versuch…');
-      await tryYtm(0, mf(null, false));
-    }
-    if (!hasAudio()) {
-      // 9. YT top-5 — title only
-      await spawnYtdlp([`ytsearch5:${query}`, ...PI_FILTERED, ...mf(null, false), ...baseArgs]);
-    }
-    if (!hasAudio()) {
-      // 10. YTM — no filter at all, take first video result
-      log(jobId, '⚠️  Letzter Versuch: keine Filter…');
-      await tryYtm(3, []);
-    }
-    if (!hasAudio()) {
-      // 11. YT — no filter
-      await spawnYtdlp([`ytsearch1:${query}`, ...PI_UNFILTERED, ...baseArgs]);
+      // 6. YT top-10 — no duration, but channel + title required
+      await spawnYtdlp([`ytsearch10:${query}`, ...PI_FILTERED_10, ...mf(null, true, true), ...baseArgs]);
     }
   } else {
     log(jobId, `🔍 Suche YT Music: "${query}"`);
@@ -360,8 +347,8 @@ async function downloadTrack({ jobId, artist, rawArtist, albumArtist, title, alb
 
   const audioFile = hasAudio() ? expectedAudio : null;
   if (!audioFile) {
-    log(jobId, '⚠️  Keine Audio-Datei gefunden');
-    return { success: true, dir };
+    log(jobId, '⚠️  Nicht eindeutig gefunden — bitte Direktlink im Importer nutzen');
+    return { success: false, notFound: true, dir };
   }
 
   return embedMetadata({ jobId, audioFile, dir, trackPrefix, safeTitle, rawArtist, artist, mainArtist, album, year, trackNum, totalTracks, discNum, discTotal, compilation, genre, artworkUrl, explicit, title: searchTitle });

backend/novasonic-server.js

@@ -601,6 +601,8 @@ app.post('/api/download', async (req, res) => {
         const result = await downloadTrack({ jobId, artist: finalArtist, rawArtist: artist, title, ...meta, sourceUrl: sourceUrl || sp.sourceUrl || undefined });
         if (result?.skipped) {
           updateJob(jobId, { status: 'done', progress: 100, message: 'Bereits vorhanden – übersprungen', skipped: true });
+        } else if (result?.notFound) {
+          updateJob(jobId, { status: 'error', message: 'Nicht eindeutig gefunden — bitte Direktlink im Importer nutzen' });
         } else {
           updateJob(jobId, { status: 'done', progress: 100, message: 'Fertig!' });
         }
@@ -653,7 +655,7 @@ app.post('/api/download', async (req, res) => {
         const plTracks = req.body.tracks || [];
         if (!plTracks.length) throw new Error('Keine Tracks übergeben');
         log(jobId, `🎵 Playlist "${title}" — ${plTracks.length} Tracks`);
-        let done = 0, skipped = 0;
+        let done = 0, skipped = 0, notFound = 0;
         const CONC = CONFIG.maxParallel || 2;
         for (let i = 0; i < plTracks.length; i += CONC) {
           const batch = plTracks.slice(i, i + CONC);
@@ -709,10 +711,13 @@ app.post('/api/download', async (req, res) => {
               log(jobId, `⚠️  Fehler bei "${batch[j].trackName || '?'}": ${r.reason?.message || r.reason}`);
             } else if (r.value?.skipped) {
               skipped++;
+            } else if (r.value?.notFound) {
+              notFound++;
+              log(jobId, `⚠️  Nicht eindeutig gefunden: "${batch[j].trackName || '?'}" — Direktlink nutzen`);
             } else {
               done++;
             }
-            updateJob(jobId, { progress: Math.round(((done + skipped) / plTracks.length) * 90) });
+            updateJob(jobId, { progress: Math.round(((done + skipped + notFound) / plTracks.length) * 90) });
           }
         }
         const allSkipped = skipped === plTracks.length;
@@ -720,7 +725,7 @@ app.post('/api/download', async (req, res) => {
           status: 'done', progress: 100, skipped: allSkipped,
           message: allSkipped
             ? `Alle ${skipped} Tracks bereits vorhanden`
-            : `Fertig! ${done} geladen${skipped ? `, ${skipped} übersprungen` : ''}`,
+            : `Fertig! ${done} geladen${skipped ? `, ${skipped} übersprungen` : ''}${notFound ? `, ${notFound} nicht gefunden` : ''}`,
         });
       }
     } catch (err) {