fix: downloads page album art, total count, and clear-completed safety

- Fix missing album art on downloads page across all sources
- Fix downloads page showing wrong total count
- Enrich missing download artwork from metadata cache
- Prevent Clear Completed from removing active download batches
- Keep download limit at 300 per performance design

web_server.py

@@ -31402,6 +31402,34 @@ def get_all_downloads_unified():
         # Sort: active first (by priority), then by timestamp desc within each group
         items.sort(key=lambda x: (x['priority'], -x['timestamp']))
 
+        # POST-LOCK: Enrich missing artwork from metadata cache (handles legacy
+        # wishlist tracks that were stored without image data)
+        items_needing_art = [it for it in items if not it.get('artwork') and it.get('title')]
+        if items_needing_art:
+            try:
+                database = get_database()
+                # Batch lookup by track name — metadata cache has deezer/itunes images
+                track_names = list({it['title'] for it in items_needing_art if it['title']})
+                if track_names:
+                    placeholders = ','.join('?' for _ in track_names)
+                    with database._get_connection() as conn:
+                        cursor = conn.cursor()
+                        cursor.execute(f"""
+                            SELECT name, image_url FROM metadata_cache_entities
+                            WHERE entity_type='track' AND name IN ({placeholders})
+                              AND image_url IS NOT NULL AND image_url != ''
+                        """, track_names)
+                        name_to_art = {}
+                        for row in cursor.fetchall():
+                            if row[0] not in name_to_art:
+                                name_to_art[row[0]] = row[1]
+                    for it in items_needing_art:
+                        cached_url = name_to_art.get(it['title'])
+                        if cached_url:
+                            it['artwork'] = cached_url
+            except Exception as cache_err:
+                logger.debug(f"Metadata cache artwork lookup failed: {cache_err}")
+
         # Build batch summaries for the batch context panel
         batch_summaries = []
         with tasks_lock:
@@ -31462,9 +31490,16 @@ def clear_completed_downloads():
             for tid in task_ids_to_remove:
                 del download_tasks[tid]
                 cleared += 1
-            # Also clean up empty batches
+            # Also clean up empty batches (but not those still actively processing)
+            active_phases = {'analysis', 'downloading', 'queued'}
             empty_batches = []
             for bid, batch in download_batches.items():
+                # Never remove batches that are still actively working
+                if batch.get('phase') in active_phases:
+                    # Still prune cleared tasks from queue
+                    remaining = [t for t in batch.get('queue', []) if t in download_tasks]
+                    batch['queue'] = remaining
+                    continue
                 remaining = [t for t in batch.get('queue', []) if t in download_tasks]
                 if not remaining:
                     empty_batches.append(bid)