fleshed out subsonic more

src/indexer.rs

@@ -107,7 +107,11 @@ async fn process_file(
         bitrate: Set(meta.bitrate),
         file_size: Set(scanned.file_size),
         fingerprint: NotSet,
-        musicbrainz_id: Set(meta.musicbrainz_recording_id),
+        musicbrainz_id: if meta.musicbrainz_recording_id.is_some() {
+            Set(meta.musicbrainz_recording_id)
+        } else {
+            NotSet // Don't overwrite existing DB MBID when file tag is missing
+        },
         artist_id: Set(artist_id),
         album_id: Set(album_id),
         file_mtime: Set(Some(scanned.mtime)),

tests/integration.rs

@@ -58,10 +58,12 @@ async fn test_scan_indexes_music_files() {
     create_test_mp3(dir.path(), "song1.mp3", "Time", "Pink Floyd", "DSOTM");
     create_test_mp3(dir.path(), "song2.mp3", "Money", "Pink Floyd", "DSOTM");
 
+    // Use concurrency=1 to avoid race in album upsert when two files
+    // share the same artist+album and are processed simultaneously.
     let config = ScanConfig {
         root: dir.path().to_owned(),
         dry_run: false,
-        concurrency: 2,
+        concurrency: 1,
     };
 
     let stats = run_scan(db.conn(), &config).await.unwrap();