iOS: Duo unfolded layout with right-edge tab rail, stems+queue deck and swap sides

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

ios/Stemify/UI/RootView.swift

@@ -2,15 +2,18 @@ import SwiftUI
 import UIKit
 
 /// The tab bar, a navigation stack per tab, the mini player and the Now Playing sheet.
-/// On an unfolded iPhone Duo the library sits on one side of the hinge and Now Playing on the other.
+/// On an unfolded iPhone Duo Now Playing takes one side of the hinge, the stems and queue (or a tab)
+/// the other, and the tabs move to a rail on the right edge beside the status bar.
 struct RootView: View {
     @State private var ui = Ui(overlays: Overlays())
+    /// Unfolded iPhone Duo: Now Playing on the left of the hinge instead of the right.
+    @AppStorage("duoSwap") private var duoSwap = false
     private var g: AppGraph { .shared }
 
     var body: some View {
         let s = g.settings
         let p = Palette.of(s.theme, s.accent)
-        DuoSplit(onSplit: { ui.setSplit($0) }) {
+        DuoSplit(swap: duoSwap, showDeck: ui.deck, onSplit: { ui.setSplit($0) }) {
         TabView(selection: Binding(get: { ui.tab }, set: { ui.selectTab($0) })) {
             ForEach(Tab.layout(s.tabLayout), id: \.self) { t in
                 NavigationStack(path: ui.path(t)) {
@@ -23,8 +26,12 @@ struct RootView: View {
             }
         }
         .modifier(GlassMiniPlayerHost())
+        } deck: {
+            NowPlayingDeck()
         } docked: {
             NowPlayingScreen(docked: true)
+        } rail: {
+            DuoRail(swap: $duoSwap)
         }
         .background(p.bg.ignoresSafeArea())
         .onChange(of: s.tabLayout) { _, _ in ui.ensureValidTab() }
@@ -135,6 +142,8 @@ private struct MiniPlayerRoom: ViewModifier {
         content.safeAreaInset(edge: .bottom, spacing: 0) {
             if !glassAccessory && !ui.split && g.playback.current != nil { Color.clear.frame(height: 66) }
         }
+        // Split, the rail stands in for the tab bar.
+        .toolbar(ui.split ? .hidden : .automatic, for: .tabBar)
     }
 }
 
@@ -142,28 +151,55 @@ private extension View {
     func miniPlayerRoom() -> some View { modifier(MiniPlayerRoom()) }
 }
 
-/// Splits the screen at the iPhone Duo's hinge (the system's division region): [library] on the
-/// leading or top side, [docked] on the other. Anywhere without an active hinge it's just [library].
-/// One layout for both states keeps the library's tab and scroll state across fold and unfold.
-private struct DuoSplit<Library: View, Docked: View>: View {
+/// Splits the screen at the iPhone Duo's hinge (the system's division region). [library] (with
+/// [deck] over it while [showDeck]) goes on one side and [docked] on the other, left and right
+/// trading places with [swap]; [rail] runs down the right edge in the status bar's strip.
+/// Anywhere without a hinge it's just [library]. The library stays put in the view tree, so its
+/// tab and scroll state survive folding, unfolding and swapping.
+private struct DuoSplit<Library: View, Deck: View, Docked: View, Rail: View>: View {
+    var swap: Bool
+    var showDeck: Bool
     var onSplit: (Bool) -> Void
     @ViewBuilder var library: Library
+    @ViewBuilder var deck: Deck
     @ViewBuilder var docked: Docked
+    @ViewBuilder var rail: Rail
+
+    private static var railWidth: CGFloat { 64 }
 
     var body: some View {
         GeometryReader { geo in
             let cut = Self.cut(geo)
+            let inset = geo.safeAreaInsets.trailing
+            // The rail lives in the status bar's strip; if that's too thin it borrows from the right pane.
+            let steal = cut == nil ? 0 : max(0, Self.railWidth - inset)
+            let flip = swap && cut?.vertical == true
             let layout = cut?.vertical == false ? AnyLayout(VStackLayout(spacing: cut?.gap ?? 0)) : AnyLayout(HStackLayout(spacing: cut?.gap ?? 0))
             layout {
-                library
-                    .frame(width: cut.map { $0.vertical ? $0.first : geo.size.width } ?? geo.size.width,
-                           height: cut.map { $0.vertical ? geo.size.height : $0.first } ?? geo.size.height)
+                ZStack {
+                    library
+                    if cut != nil && showDeck { deck.transition(.opacity) }
+                }
+                .environment(\.layoutDirection, .leftToRight)
+                .frame(width: cut.map { $0.vertical ? (flip ? $0.second - steal : $0.first) : geo.size.width - steal } ?? geo.size.width,
+                       height: cut.map { $0.vertical ? geo.size.height : $0.first } ?? geo.size.height)
                 if let cut {
                     docked
-                        .frame(width: cut.vertical ? cut.second : geo.size.width,
+                        .environment(\.layoutDirection, .leftToRight)
+                        .frame(width: cut.vertical ? (flip ? cut.first : cut.second - steal) : geo.size.width - steal,
                                height: cut.vertical ? geo.size.height : cut.second)
                 }
             }
+            // Right-to-left lays the same two children out mirrored, so swapping doesn't rebuild either.
+            .environment(\.layoutDirection, flip ? .rightToLeft : .leftToRight)
+            .frame(maxWidth: .infinity, maxHeight: .infinity, alignment: .topLeading)
+            .overlay(alignment: .topTrailing) {
+                if cut != nil {
+                    rail.frame(width: max(inset, Self.railWidth), height: geo.size.height).offset(x: inset)
+                }
+            }
+            .animation(.spring(duration: 0.4, bounce: 0.1), value: flip)
+            .animation(.easeInOut(duration: 0.2), value: showDeck)
             .onChange(of: cut != nil, initial: true) { _, on in onSplit(on) }
         }
     }
@@ -193,3 +229,41 @@ private struct DuoSplit<Library: View, Docked: View>: View {
         return c.first > 200 && c.second > 200 ? c : nil
     }
 }
+
+/// The tab bar's stand-in on an unfolded iPhone Duo: Now Playing's stems and queue, the tabs, and
+/// a button that swaps which side of the hinge Now Playing sits on.
+private struct DuoRail: View {
+    @Binding var swap: Bool
+    @Environment(Ui.self) private var ui
+    @Environment(\.palette) private var p
+
+    var body: some View {
+        VStack(spacing: 4) {
+            Spacer(minLength: 48)
+            item("Playing", "waveform", on: ui.deck) { ui.showDeck() }
+            ForEach(ui.tabs, id: \.self) { t in
+                item(t.rawValue, t.icon, on: !ui.deck && ui.tab == t) { ui.selectTab(t) }
+            }
+            Capsule().fill(p.label3.opacity(0.4)).frame(width: 24, height: 2).padding(.vertical, 8)
+            item("Swap", "arrow.left.arrow.right", on: false) { swap.toggle() }
+            Spacer(minLength: 48)
+        }
+        .frame(maxWidth: .infinity)
+    }
+
+    private func item(_ title: String, _ icon: String, on: Bool, _ action: @escaping () -> Void) -> some View {
+        Button { withAnimation(.snappy(duration: 0.25)) { action() } } label: {
+            VStack(spacing: 3) {
+                Image(systemName: icon).font(.system(size: 19, weight: on ? .semibold : .regular)).frame(height: 24)
+                Text(title).font(.system(size: 10, weight: .medium)).lineLimit(1).minimumScaleFactor(0.7)
+            }
+            .foregroundStyle(on ? p.accent : p.label2)
+            .frame(width: 56, height: 52)
+            .background(on ? p.accent.opacity(0.14) : .clear, in: RoundedRectangle(cornerRadius: 12, style: .continuous))
+            .contentShape(Rectangle())
+        }
+        .buttonStyle(PressFade())
+        .accessibilityLabel(title)
+        .accessibilityAddTraits(on ? .isSelected : [])
+    }
+}