iOS 1.0.8: stem playlists, karaoke softness slider in lyrics

- Playlists tab splits into Plex and Stem. Plex playlists are unchanged and
  now show their custom poster when one is set.
- Stem playlists live on the device; each song keeps its own mix. Add from
  any song or collection menu, or copy a whole Plex playlist.
- Queue items can carry a mix, which wins over the song's saved mix.
- Softness slider under the Vocals picker in lyrics when set to Soft.

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

ios/Stemify/Playback/PlaybackManager.swift

@@ -46,6 +46,8 @@ enum SourceKind { case None, Stems, Original }
 struct QueueItem: Codable, Hashable, Identifiable {
     var uid: Int64
     var track: Track
+    /// Set when the song came from a stem playlist; it plays with this mix instead of its saved one.
+    var mix: [String: StemSetting]?
     var id: Int64 { uid }
 }
 
@@ -204,16 +206,17 @@ final class PlaybackManager: StemEngineListener, @unchecked Sendable {
 
     // ---- queue --------------------------------------------------------------------------
 
-    private func items(_ tracks: [Track]) -> [QueueItem] {
-        tracks.map { t in
+    private func items(_ tracks: [Track], _ mixes: [[String: StemSetting]]? = nil) -> [QueueItem] {
+        tracks.enumerated().map { i, t in
             defer { nextUid += 1 }
-            return QueueItem(uid: nextUid, track: t)
+            return QueueItem(uid: nextUid, track: t, mix: mixes.flatMap { i < $0.count ? $0[i] : nil })
         }
     }
 
-    func playTracks(_ tracks: [Track], start: Int = 0, shuffle doShuffle: Bool = false) {
+    /// `mixes` lines up with `tracks`: each song plays with its own mix (stem playlists).
+    func playTracks(_ tracks: [Track], mixes: [[String: StemSetting]]? = nil, start: Int = 0, shuffle doShuffle: Bool = false) {
         if tracks.isEmpty { return }
-        let items = items(tracks)
+        let items = items(tracks, mixes)
         if doShuffle {
             unshuffled = items
             let first = start > 0 && start < items.count ? items[start] : items.randomElement()!
@@ -228,12 +231,12 @@ final class PlaybackManager: StemEngineListener, @unchecked Sendable {
         }
     }
 
-    func playNext(_ tracks: [Track]) { insert(index + 1, tracks) }
-    func addToQueue(_ tracks: [Track]) { insert(queue.count, tracks) }
+    func playNext(_ tracks: [Track], mixes: [[String: StemSetting]]? = nil) { insert(index + 1, tracks, mixes) }
+    func addToQueue(_ tracks: [Track], mixes: [[String: StemSetting]]? = nil) { insert(queue.count, tracks, mixes) }
 
-    private func insert(_ at: Int, _ tracks: [Track]) {
+    private func insert(_ at: Int, _ tracks: [Track], _ mixes: [[String: StemSetting]]? = nil) {
         if tracks.isEmpty { return }
-        let items = items(tracks)
+        let items = items(tracks, mixes)
         var q = queue
         q.insert(contentsOf: items, at: min(max(at, 0), q.count))
         queue = q
@@ -415,10 +418,11 @@ final class PlaybackManager: StemEngineListener, @unchecked Sendable {
         pushMix()
     }
 
-    /// The mix a song starts with: karaoke if that's on, else the song's saved mix, else cleared (or kept, per settings).
-    private func startMix(_ t: Track) -> [String: StemSetting] {
+    /// The mix a song starts with: karaoke if that's on, else its stem playlist mix, else the song's saved mix,
+    /// else cleared (or kept, per settings).
+    private func startMix(_ item: QueueItem) -> [String: StemSetting] {
         if karaoke { return karaokeMix }
-        return songMixes[t.ratingKey] ?? (settings.keepStemMix ? mix : [:])
+        return item.mix ?? songMixes[item.track.ratingKey] ?? (settings.keepStemMix ? mix : [:])
     }
 
     /// How much of the singer is left in karaoke mode. Soft is a guide under your own voice, as quiet as settings say.
@@ -527,7 +531,7 @@ final class PlaybackManager: StemEngineListener, @unchecked Sendable {
         if play && !activateSession() { return }
         playWhenReady = play
         buffering = true
-        mix = startMix(item.track)
+        mix = startMix(item)
         changed()
         save()
         loadTask = Task { @MainActor [weak self] in
@@ -700,7 +704,7 @@ final class PlaybackManager: StemEngineListener, @unchecked Sendable {
         guard let item = current else { return }
         durationMs = item.track.durationMs
         waveform = nil
-        mix = startMix(item.track)
+        mix = startMix(item)
         source = currentEntry != nil ? .Stems : .Original
         stemNames = Stems.sort(currentEntry?.stems.map(\.name) ?? ["mix"])
         pushMix()

ios/Stemify/Playback/StemPlaylists.swift

@@ -0,0 +1,86 @@
+import Foundation
+import Observation
+
+/// One song in a stem playlist, saved with the mix it plays with.
+struct StemPlaylistItem: Codable, Hashable, Identifiable {
+    var uid = UUID().uuidString
+    var track: Track
+    var mix: [String: StemSetting]
+    var id: String { uid }
+}
+
+struct StemPlaylist: Codable, Hashable, Identifiable {
+    var id = UUID().uuidString
+    var title: String
+    var items: [StemPlaylistItem] = []
+    var created = Date()
+    var updated = Date()
+
+    var tracks: [Track] { items.map(\.track) }
+    var mixes: [[String: StemSetting]] { items.map(\.mix) }
+    var thumb: String? { items.lazy.compactMap(\.track.thumb).first }
+    var durationMs: Int64 { items.reduce(0) { $0 + $1.track.durationMs } }
+}
+
+/// Playlists that live on this device only: each song keeps its own stem mix (instrumentals, a cappellas…).
+/// Plex playlists can't hold a mix, so these are separate.
+@MainActor @Observable
+final class StemPlaylists {
+    private(set) var lists: [StemPlaylist] = []
+    @ObservationIgnored private let file: URL
+
+    /// Every stem a song can have, for naming saved mixes without loading the song.
+    static let allStems = ["vocals", "drums", "bass", "guitar", "piano", "other"]
+
+    init(dir: URL) {
+        file = dir.appendingPathComponent("stem-playlists.json")
+        lists = (try? JSONDecoder().decode([StemPlaylist].self, from: Data(contentsOf: file))) ?? []
+    }
+
+    func list(_ id: String) -> StemPlaylist? { lists.first { $0.id == id } }
+
+    @discardableResult
+    func create(_ title: String, tracks: [Track] = [], mix: [String: StemSetting] = [:]) -> StemPlaylist {
+        let pl = StemPlaylist(title: title, items: tracks.map { StemPlaylistItem(track: $0, mix: MixPresets.normalized(mix)) })
+        lists.insert(pl, at: 0)
+        save()
+        return pl
+    }
+
+    func add(_ id: String, tracks: [Track], mix: [String: StemSetting]) {
+        edit(id) { $0.items += tracks.map { StemPlaylistItem(track: $0, mix: MixPresets.normalized(mix)) } }
+    }
+
+    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]) {
+        edit(id) { pl in if let i = pl.items.firstIndex(where: { $0.uid == item }) { pl.items[i].mix = MixPresets.normalized(mix) } }
+    }
+    func rename(_ id: String, _ title: String) { edit(id) { $0.title = title } }
+
+    func delete(_ id: String) {
+        lists.removeAll { $0.id == id }
+        save()
+    }
+
+    /// "Instrumental", "A Cappella"… or "Custom Mix" for a hand-made one.
+    static func label(_ mix: [String: StemSetting]) -> String {
+        if MixPresets.normalized(mix).isEmpty { return MixPresets.full.label }
+        if MixPresets.current(allStems, mix) == MixPresets.karaoke { return "Instrumental" }
+        return MixPresets.current(allStems, mix)?.label ?? "Custom Mix"
+    }
+
+    private func edit(_ id: String, _ change: (inout StemPlaylist) -> Void) {
+        guard let i = lists.firstIndex(where: { $0.id == id }) else { return }
+        change(&lists[i])
+        lists[i].updated = Date()
+        save()
+    }
+
+    private func save() {
+        let all = lists, file = file
+        DispatchQueue.global(qos: .utility).async {
+            if let data = try? JSONEncoder().encode(all) { try? data.write(to: file, options: .atomic) }
+        }
+    }
+}