iOS: stem playlist refresh and covers, download queue page, reorderable Library, whole-library radio

Co-Authored-By: Claude Sonnet 5.5 <noreply@anthropic.com>

ios/Stemify/Playback/StemPlaylists.swift

@@ -15,10 +15,12 @@ struct StemPlaylist: Codable, Hashable, Identifiable {
     var items: [StemPlaylistItem] = []
     var created = Date()
     var updated = Date()
+    /// Cover picked by the user; nil follows the first song.
+    var artThumb: String?
 
     var tracks: [Track] { items.map(\.track) }
     var mixes: [[String: StemSetting]] { items.map(\.mix) }
-    var thumb: String? { items.lazy.compactMap(\.track.thumb).first }
+    var thumb: String? { artThumb ?? items.lazy.compactMap(\.track.thumb).first }
     var durationMs: Int64 { items.reduce(0) { $0 + $1.track.durationMs } }
 }
 
@@ -51,6 +53,32 @@ final class StemPlaylists {
         edit(id) { $0.items += tracks.map { StemPlaylistItem(track: $0, mix: MixPresets.normalized(mix)) } }
     }
 
+    func setArt(_ id: String, _ thumb: String?) { edit(id) { $0.artThumb = thumb } }
+
+    /// Re-reads every song from the library so renamed, retagged or re-added songs match again.
+    /// Keeps each item's uid and mix, and leaves songs the library can't find as they are.
+    /// Returns true when anything changed.
+    @discardableResult
+    func refresh(albumTracks: (String) async throws -> [Track]) async -> Bool {
+        var fresh: [String: [Track]] = [:]
+        for key in Set(lists.flatMap { $0.items.compactMap(\.track.albumKey) }) {
+            if let t = try? await albumTracks(key) { fresh[key] = t }
+        }
+        var changed = false
+        for li in lists.indices {
+            for ii in lists[li].items.indices {
+                let old = lists[li].items[ii].track
+                guard let key = old.albumKey, let pool = fresh[key] else { continue }
+                guard var new = pool.first(where: { $0.ratingKey == old.ratingKey })
+                    ?? pool.first(where: { $0.title == old.title && $0.artist == old.artist }) else { continue }
+                if new.stemKey == nil { new.stemKey = old.stemKey }
+                if new != old { lists[li].items[ii].track = new; changed = true }
+            }
+        }
+        if changed { save() }
+        return changed
+    }
+
     func setItems(_ id: String, _ items: [StemPlaylistItem]) { edit(id) { $0.items = items } }
     func remove(_ id: String, item: String) { edit(id) { $0.items.removeAll { $0.uid == item } } }
     func setMix(_ id: String, item: String, _ mix: [String: StemSetting]) {