fix: wire _findFileByStem into both file resolution fallback chains

Handles "File not found" for songs with non-standard folder/artist names
(e.g. artist separator • or year-only album folders) by doing a deep
recursive title-stem search as a last resort after rebase and dir scan.

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

backend/novasonic-server.js

@@ -91,6 +91,31 @@ function _findFileInDir(dir, basename) {
   return null;
 }
 
+// Last-resort: deep recursive search by title stem (handles folder renames after metadata edit).
+// Convention: MusicRoot/AlbumArtist/Album/{01 - }Artist - Title.ext
+// The title stem is everything after the optional "NN - Artist - " prefix.
+// We match any audio file whose stem ends with the same title words.
+function _findFileByStem(dir, titleStem, depth = 0) {
+  if (depth > 4) return null;
+  try {
+    for (const entry of fs.readdirSync(dir, { withFileTypes: true })) {
+      if (entry.isDirectory()) {
+        const found = _findFileByStem(path.join(dir, entry.name), titleStem, depth + 1);
+        if (found) return found;
+      } else if (AUDIO_EXT_RE.test(entry.name)) {
+        // Strip extension, strip leading "NN - ", then strip optional "Artist - " prefix
+        const bare = entry.name.replace(AUDIO_EXT_RE, '').replace(/^\d+\s*-\s*/, '');
+        // bare may be "Artist - Title" or just "Title" — match from the end
+        const bareStem = bare.toLowerCase();
+        if (bareStem === titleStem || bareStem.endsWith(' - ' + titleStem) || bareStem.endsWith(titleStem)) {
+          return path.join(dir, entry.name);
+        }
+      }
+    }
+  } catch {}
+  return null;
+}
+
 // ─── QUEUE ────────────────────────────────────────────────────────────────────
 let activeDownloads = 0;
 const downloadQueue = [];
@@ -701,9 +726,11 @@ app.get('/api/song-sorttags', async (req, res) => {
     const fileName   = path.basename(filePath);
     const rebased    = _rebasePath(filePath, CONFIG.musicPath);
     const rebasedDir = rebased ? path.dirname(rebased) : null;
+    const titleStem  = fileName.replace(AUDIO_EXT_RE, '').replace(/^\d+\s*-\s*/, '').toLowerCase();
     const found      = rebased
       || _findFileRecursive(CONFIG.musicPath, fileName)
-      || _findFileInDir(rebasedDir || path.dirname(filePath), fileName);
+      || _findFileInDir(rebasedDir || path.dirname(filePath), fileName)
+      || _findFileByStem(CONFIG.musicPath, titleStem);
     if (found) filePath = found; else return res.status(404).json({ error: 'File not found' });
   }
   try {
@@ -834,9 +861,11 @@ app.post('/api/edit-metadata', async (req, res) => {
     // Also check the original dir — the file may have been renamed (e.g. artist added to filename)
     // but Navidrome's index is stale and still points to the old name.
     const originalDir = path.dirname(filePath);
+    const titleStem  = fileName.replace(AUDIO_EXT_RE, '').replace(/^\d+\s*-\s*/, '').toLowerCase();
     const found = rebased
       || _findFileRecursive(CONFIG.musicPath, fileName)
-      || _findFileInDir(rebasedDir || originalDir, fileName);
+      || _findFileInDir(rebasedDir || originalDir, fileName)
+      || _findFileByStem(CONFIG.musicPath, titleStem);
     if (found) { filePath = found; }
     else return res.status(404).json({ error: `File not found: ${filePath} (music root: ${CONFIG.musicPath})` });
   }