fix(config): improve auto-link UX; fix song update in background job; upsert MusicFile on complex matching

packages/backend/src/services/backgroundJobService.ts

@@ -572,12 +572,13 @@ class BackgroundJobService {
             songUpdates.push({
               updateOne: {
                 filter: { _id: bestMatch.song._id },
-                update: { 
-                  $addToSet: { 
-                    s3File: {
-                      musicFileId: musicFile._id,
-                      hasS3File: true
-                    }
+                update: {
+                  $set: {
+                    's3File.musicFileId': musicFile._id,
+                    's3File.s3Key': musicFile.s3Key,
+                    's3File.s3Url': musicFile.s3Url,
+                    's3File.streamingUrl': musicFile.s3Key ? `${process.env.S3_ENDPOINT}/${process.env.S3_BUCKET_NAME}/${musicFile.s3Key}` : undefined,
+                    's3File.hasS3File': true
                   }
                 }
               }

packages/frontend/src/components/SongMatching.tsx

@@ -114,24 +114,25 @@ export const SongMatching: React.FC = () => {
         }),
       });
 
-      if (response.ok) {
-        const result = await response.json();
-        toast({
-          title: 'Auto-linking Complete',
-          description: `Linked ${result.result.linked} files, ${result.result.unmatched} unmatched`,
-          status: 'success',
-          duration: 5000,
-          isClosable: true,
-        });
-        loadData(); // Refresh data
-      } else {
-        throw new Error('Auto-linking failed');
+      if (!response.ok) {
+        const errText = await response.text();
+        throw new Error(errText || 'Auto-linking failed');
       }
+
+      const result = await response.json();
+      toast({
+        title: 'Auto-linking Started',
+        description: `Job ${result.jobId} started.`,
+        status: 'info',
+        duration: 4000,
+        isClosable: true,
+      });
+      // Do not call loadData immediately; background job UI will refresh stats as it completes
     } catch (error) {
       console.error('Error during auto-linking:', error);
       toast({
         title: 'Error',
-        description: 'Failed to auto-link music files',
+        description: error instanceof Error ? error.message : 'Failed to auto-link music files',
         status: 'error',
         duration: 3000,
         isClosable: true,