diff --git a/Controls/TopBar.xaml b/Controls/TopBar.xaml
index cb3c008..71c6598 100644
--- a/Controls/TopBar.xaml
+++ b/Controls/TopBar.xaml
@@ -53,26 +53,6 @@
                 </TextBlock>
             </Button>
 
-            <!-- EDIT: explicit toggle. Neutral = off (chat), blue = on (layers/properties). The
-                 trigger used to set the SAME colour as the resting state, so the button never
-                 looked pressed. Right edge aligns with the layers panel below. -->
-            <ToggleButton Grid.Column="1" IsChecked="{Binding EditingActive, Mode=TwoWay}" Content="EDIT"
-                          Cursor="Hand" Height="32" Padding="14,0" Margin="18,0,0,2"
-                          HorizontalAlignment="Right" VerticalAlignment="Center"
-                          FontWeight="Bold" FontSize="12" Foreground="{StaticResource Brush.OnAccent}" BorderThickness="0">
-                <ToggleButton.Template>
-                    <ControlTemplate TargetType="ToggleButton">
-                        <Border x:Name="EditBody" Background="{StaticResource Brush.SurfaceContainerHigh}" CornerRadius="4" Padding="{TemplateBinding Padding}">
-                            <ContentPresenter HorizontalAlignment="Center" VerticalAlignment="Center"/>
-                        </Border>
-                        <ControlTemplate.Triggers>
-                            <Trigger Property="IsChecked" Value="True">
-                                <Setter TargetName="EditBody" Property="Background" Value="{StaticResource Brush.Tertiary}"/>
-                            </Trigger>
-                        </ControlTemplate.Triggers>
-                    </ControlTemplate>
-                </ToggleButton.Template>
-            </ToggleButton>
         </Grid>
 
         <!-- Session surface (top bar redesign): the bar is ONE surface rendered by
@@ -81,6 +61,24 @@
              reality line + End so nothing mid-session can be re-armed. -->
         <StackPanel Grid.Column="1" Orientation="Horizontal"
                     HorizontalAlignment="Center" VerticalAlignment="Center">
+            <!-- THE decision (creator ruling 2026-11-12): [ Build Scenes ][ Record / Go Live ].
+                 Build Scenes is the new edit mode — there is no separate EDIT button, so the
+                 question "which world am I in?" and "can I edit?" cannot disagree. Clicking the
+                 highlighted half re-enters it, which is how a creator gets back to the layers
+                 during a session. -->
+            <Border Background="{StaticResource Brush.SurfaceContainerLowest}" CornerRadius="4"
+                    Padding="2" Height="32" VerticalAlignment="Center" Margin="0,0,12,0">
+                <StackPanel Orientation="Horizontal">
+                    <Button Style="{StaticResource WorldSegmentButton}" Tag="{Binding IsBuildWorld}"
+                            Command="{Binding EnterBuildWorldCommand}" Padding="12,0"
+                            Content="Build Scenes" FontSize="12" FontWeight="Bold"
+                            ToolTip="Edit layers, scenes and webcam placement"/>
+                    <Button Style="{StaticResource WorldSegmentButton}" Tag="{Binding IsOutputWorld}"
+                            Command="{Binding EnterOutputWorldCommand}" Padding="12,0"
+                            Content="Record / Go Live" FontSize="12" FontWeight="Bold"
+                            ToolTip="Choose the output and start the session"/>
+                </StackPanel>
+            </Border>
             <!-- IDLE: the mode switch + the action(s) of the armed world. The three
                  controls share one height (build 77 feedback) so they read as one
                  family — segments host, Start/Go Live, and Test all sit at 32. -->
diff --git a/Themes/Controls.xaml b/Themes/Controls.xaml
index f866575..fb9acf0 100644
--- a/Themes/Controls.xaml
+++ b/Themes/Controls.xaml
@@ -1002,6 +1002,33 @@
     <!-- REC / ON-AIR segment pills: an armed session control reads red, because red is what
          "live or recording" means (DESIGN.md). Kept separate from SegmentToggle so the Rect|Circle
          choice in the properties panel stays the interactive blue. -->
+    <!-- The top bar's world segment (creator ruling 2026-11-12): [ Build Scenes ][ Record / Go Live ].
+         A Button, not a ToggleButton — the highlight follows the view model, so a click must never be
+         what sets it. Each button passes its own world flag in Tag and one DataTrigger paints it. -->
+    <Style x:Key="WorldSegmentButton" TargetType="Button">
+        <Setter Property="Background" Value="Transparent"/>
+        <Setter Property="Foreground" Value="{StaticResource Brush.OnAccent}"/>
+        <Setter Property="BorderThickness" Value="0"/>
+        <Setter Property="Cursor" Value="Hand"/>
+        <Setter Property="Height" Value="28"/>
+        <Setter Property="VerticalAlignment" Value="Center"/>
+        <Setter Property="Template">
+            <Setter.Value>
+                <ControlTemplate TargetType="Button">
+                    <Border x:Name="Face" Background="{TemplateBinding Background}"
+                            CornerRadius="3" Padding="{TemplateBinding Padding}">
+                        <ContentPresenter HorizontalAlignment="Center" VerticalAlignment="Center"/>
+                    </Border>
+                </ControlTemplate>
+            </Setter.Value>
+        </Setter>
+        <Style.Triggers>
+            <DataTrigger Binding="{Binding Tag, RelativeSource={RelativeSource Self}}" Value="True">
+                <Setter Property="Background" Value="{StaticResource Brush.Primary}"/>
+            </DataTrigger>
+        </Style.Triggers>
+    </Style>
+
     <Style x:Key="RecordPillToggle" TargetType="ToggleButton" BasedOn="{StaticResource SegmentToggle}">
         <!-- SegmentToggle's template hard-codes a Transparent face and paints the checked state
              itself, so an armed pill needs its own template that honours Background. -->
diff --git a/ViewModels/MainViewModel.TopBar.cs b/ViewModels/MainViewModel.TopBar.cs
new file mode 100644
index 0000000..340f6bc
--- /dev/null
+++ b/ViewModels/MainViewModel.TopBar.cs
@@ -0,0 +1,53 @@
+using System.Windows.Input;
+using ytLive.Helpers;
+
+namespace ytLive.ViewModels;
+
+/// <summary>Which half of the top bar's dual segment is in force.</summary>
+public enum BarWorld
+{
+    /// <summary>Build Scenes — the edit surface. The default at launch (creator ruling 2026-11-12).</summary>
+    Build,
+
+    /// <summary>Record / Go Live — the output surface: which output, and the one action that starts it.</summary>
+    Output,
+}
+
+/// <summary>
+/// The top bar's one decision (creator ruling 2026-11-12): <c>[ Build Scenes ][ Record / Go Live ]</c>.
+/// Build Scenes <b>is</b> edit mode — there is no separate EDIT toggle any more, so "may I edit?" and
+/// "which world am I in?" cannot disagree.
+///
+/// <para>Clicking the highlighted segment is not a no-op: it re-enters that world, which matters while a
+/// session runs because Build Scenes is the only way back to the layers (see
+/// <see cref="LockEditWhileLive"/>).</para>
+/// </summary>
+public partial class MainViewModel
+{
+    private BarWorld _barWorld = BarWorld.Build;
+
+    public BarWorld BarWorld => _barWorld;
+
+    public bool IsBuildWorld => _barWorld == BarWorld.Build;
+    public bool IsOutputWorld => _barWorld == BarWorld.Output;
+
+    public ICommand EnterBuildWorldCommand { get; private set; } = null!;
+    public ICommand EnterOutputWorldCommand { get; private set; } = null!;
+
+    private void InitializeWorldCommands()
+    {
+        EnterBuildWorldCommand = new RelayCommand(_ => EnterWorld(BarWorld.Build));
+        EnterOutputWorldCommand = new RelayCommand(_ => EnterWorld(BarWorld.Output));
+    }
+
+    /// <summary>Switches worlds. Re-entering the current one still re-asserts its edit state, which is
+    /// what lets a creator take EDIT back mid-show by clicking Build Scenes.</summary>
+    internal void EnterWorld(BarWorld world)
+    {
+        _barWorld = world;
+        OnPropertyChanged(nameof(BarWorld));
+        OnPropertyChanged(nameof(IsBuildWorld));
+        OnPropertyChanged(nameof(IsOutputWorld));
+        EditingActive = world == BarWorld.Build;
+    }
+}
diff --git a/ViewModels/MainViewModel.cs b/ViewModels/MainViewModel.cs
index 459e26e..f4c86e2 100644
--- a/ViewModels/MainViewModel.cs
+++ b/ViewModels/MainViewModel.cs
@@ -342,6 +342,7 @@ public partial class MainViewModel : ViewModelBase
         OpenHotkeyConfigCommand = new RelayCommand(_ => OpenHotkeyConfig());
         ChangeAccountCommand = new RelayCommand(_ => _ = ChangeAccountAsync());
         LogoutCommand = new RelayCommand(_ => _ = SignOutYouTubeAsync());
+        InitializeWorldCommands();
 
         _layoutStore = new LayoutStore(LayoutPathOverride ?? DefaultLayoutPath);
         _activeLayoutPath = _layoutStore.ActivePath;
diff --git a/docs/ai/ui-surface.md b/docs/ai/ui-surface.md
index 125f590..aee2818 100644
--- a/docs/ai/ui-surface.md
+++ b/docs/ai/ui-surface.md
@@ -145,6 +145,14 @@ Placement math itself is covered by `WindowPlacementTests` (pure function, no HW
   `FormattedText` — **measure, don't guess**) plus the field's padding and border. Guard:
   `ytLive.Tests/GeometryFieldWidthTests.cs`
 - Resolution tiers: 1080p60@12 (default) → 1080p30@10 → 720p60@6 → 720p30@6 → **Vertical 1080p30@10 and 1080p60@12 (9:16, 1080×1920)** — the `@` is the CBR target the encoder is asked to hold, between YouTube's H.264 recommendation and the practitioner sweet spot (its 14/17/8 recommendations are the max, the tier minimums 5/6/3 the step-down floor). Vertical mirrors its landscape pair: same pixel count, same rate. The old flat 8 Mbps was an inherited round number, not a measurement. The composition master frame is **always 1920×1080** — a tier is an output rect + target resolution over that master, so source geometry is never rewritten (no rounding drift). 16:9 tiers use the full frame; vertical tiers use a centered **607×1080** window and the preview dims the cropped side strips at 55% black with an accent outline (semi-crop — the cut area stays visible). A resolution badge in the preview corner shows the active tier. The resolution picker and live readouts (bitrate/FPS/dropped/duration) are in the top-left cell above the layers panel; the bottom bar is an empty height-preserving spacer. Under the picker sits the creator's own **rate box** (Mbps, per tier, persisted as `Video.Rate.<tier>`): the tier chooses geometry, the box chooses bits, clamped at the tier's YouTube minimum and otherwise unbounded because live step-down is the thing that catches a wrong guess. Its tooltip carries YouTube's recommendation for the tier (`Models/RateLadder`). Every consumer — encoder options, step-down policy, clip buffer — reads `MainViewModel.EffectiveQuality`, never the raw tier. A **tooltip** explains finding upload bandwidth — an in-app speed test was deliberately dropped (unreliable). The future encoder crops the master to the rect and scales to the tier's Width×Height
+- **The top bar has ONE decision (creator ruling 2026-11-12): `[ Build Scenes ][ Record / Go Live ]`.**
+  Build Scenes ships highlighted and **is** edit mode — the standalone EDIT toggle is gone, so "which
+  world am I in?" and "can I edit?" cannot disagree (`MainViewModel.TopBar.cs`, `BarWorld`). The segment
+  leads the centre cluster and stays present in every state; clicking the highlighted half re-enters it,
+  which is how a creator gets back to the layers during a session. `WorldSegmentButton`
+  (`Themes/Controls.xaml`) is a Button, not a ToggleButton — the highlight follows the view model, and a
+  click must never be what sets it. Next in the same redesign: the output switch (`Output [YouTube]
+  [Local MP4] One output at a time`, MP4 default) and an output-dependent primary action.
 - **Editing during a session is a setting (creator ruling 2026-11-12).** `App.LockEditWhileLive` is off
   by default: a show does not take EDIT away, so a creator may move a layer or resize a webcam while
   live. On restores the old gun-safety — go-live flips EDIT off, stop flips it back, and only because
diff --git a/ytLive.Tests/TopBarWorldTests.cs b/ytLive.Tests/TopBarWorldTests.cs
new file mode 100644
index 0000000..691be32
--- /dev/null
+++ b/ytLive.Tests/TopBarWorldTests.cs
@@ -0,0 +1,55 @@
+using System;
+using System.IO;
+using Xunit;
+using ytLive.ViewModels;
+
+namespace ytLive.Tests;
+
+/// <summary>
+/// The top bar's one decision: <c>[ Build Scenes ][ Record / Go Live ]</c>. Build Scenes ships
+/// highlighted, and it <b>is</b> edit mode — the old EDIT toggle is gone, so "can I edit?" and "which
+/// world am I in?" cannot disagree.
+/// </summary>
+[Collection("MainViewModelLayoutPath")]
+public class TopBarWorldTests
+{
+    [Fact]
+    public void Build_scenes_is_the_default_world_and_is_the_only_place_editing_lives()
+    {
+        var db = Path.Combine(Path.GetTempPath(), $"llamacasty-world-{Guid.NewGuid():N}.db");
+        MainViewModel.LayoutPathOverride = db;
+        try
+        {
+            var vm = new MainViewModel();
+
+            // Launch state: Build Scenes highlighted, editing on.
+            Assert.Equal(BarWorld.Build, vm.BarWorld);
+            Assert.True(vm.IsBuildWorld);
+            Assert.False(vm.IsOutputWorld);
+            Assert.True(vm.IsEditMode);
+
+            // Record / Go Live leaves edit mode — the output surface has nothing to drag.
+            vm.EnterOutputWorldCommand.Execute(null);
+            Assert.Equal(BarWorld.Output, vm.BarWorld);
+            Assert.True(vm.IsOutputWorld);
+            Assert.False(vm.IsBuildWorld);
+            Assert.False(vm.IsEditMode);
+
+            // Clicking the highlighted half is not a no-op: it re-enters that world, which is how a
+            // creator takes editing back during a session.
+            vm.EnterBuildWorldCommand.Execute(null);
+            Assert.True(vm.IsBuildWorld);
+            Assert.True(vm.IsEditMode);
+
+            // …and re-entering the world already in force still re-asserts its edit state.
+            vm.EditingActive = false;
+            vm.EnterBuildWorldCommand.Execute(null);
+            Assert.True(vm.IsEditMode);
+        }
+        finally
+        {
+            MainViewModel.LayoutPathOverride = null;
+            try { File.Delete(db); } catch (IOException) { }
+        }
+    }
+}
diff --git a/ytLive.Tests/UiShellTests.cs b/ytLive.Tests/UiShellTests.cs
index f82efc1..b419f9c 100644
--- a/ytLive.Tests/UiShellTests.cs
+++ b/ytLive.Tests/UiShellTests.cs
@@ -27,12 +27,13 @@ public class UiShellTests
         Assert.Contains("Brush.Youtube", tokens);
         Assert.Equal(2, Count(preview, "Background=\"{StaticResource Brush.Youtube}\""));
 
-        // 2. EDIT: resting face differs from the armed face, and the label follows it.
-        Assert.Contains("x:Name=\"EditBody\" Background=\"{StaticResource Brush.SurfaceContainerHigh}\"", topBar);
-        Assert.Contains("<Setter TargetName=\"EditBody\" Property=\"Background\" Value=\"{StaticResource Brush.Tertiary}\"/>", topBar);
-        // The label is white in BOTH states — only the fill changes. A muted resting colour is
-        // what made it illegible on the dark bar (creator, 2026-10-30).
-        Assert.Contains("FontSize=\"12\" Foreground=\"{StaticResource Brush.OnAccent}\"", topBar);
+        // 2. The world segment replaced the EDIT toggle (creator ruling 2026-11-12): both halves are
+        //    present, each lit by its own world flag through the shared style.
+        Assert.Contains("Content=\"Build Scenes\"", topBar);
+        Assert.Contains("Content=\"Record / Go Live\"", topBar);
+        Assert.Contains("Tag=\"{Binding IsBuildWorld}\"", topBar);
+        Assert.Contains("Tag=\"{Binding IsOutputWorld}\"", topBar);
+        Assert.DoesNotContain("x:Name=\"EditBody\"", topBar);
 
         // 3. Active scene = orange; live stays red.
         Assert.Contains("IsStaged}\" Value=\"True\">\n                                        <Setter Property=\"BorderBrush\" Value=\"{StaticResource Brush.Attention}\"/>", strip);
@@ -91,11 +92,12 @@ public class UiShellTests
         Assert.Contains("MouseLeftButtonUp=\"SettingsTab_Click\"", gear);
         Assert.DoesNotContain("ToolTip=\"Settings\"", topBar);
 
-        // EDIT stays in the left brand cluster, before the centre session cluster.
-        var edit = topBar.IndexOf("EditingActive", System.StringComparison.Ordinal);
+        // The world segment leads the centre cluster; the brand column carries no edit control.
         var centre = topBar.IndexOf("<StackPanel Grid.Column=\"1\"", System.StringComparison.Ordinal);
-        Assert.True(edit > 0 && centre > edit,
-            "the EDIT toggle must appear before the centre (session) cluster");
+        var segment = topBar.IndexOf("Content=\"Build Scenes\"", System.StringComparison.Ordinal);
+        Assert.True(centre > 0 && segment > centre,
+            "the [ Build Scenes ][ Record / Go Live ] segment must lead the centre cluster");
+        Assert.DoesNotContain("x:Name=\"EditBody\"", topBar);
     }
 
     private static int Count(string haystack, string needle)