Use the native Sidebar background material

TFM/App/RootView.swift

@@ -31,16 +31,20 @@ struct RootView: View {
         @Bindable var presentations = window.presentations
 
         NavigationSplitView(columnVisibility: sidebarVisibility) {
-            ZStack {
-                SidebarGlassBackground()
-                    .ignoresSafeArea()
-                WindowSidebarView()
-            }
-            .navigationSplitViewColumnWidth(
-                min: Metrics.Sidebar.min,
-                ideal: min(Metrics.Sidebar.ideal, sidebarMaxWidth),
-                max: sidebarMaxWidth
-            )
+            WindowSidebarView()
+                .background {
+                    // Modern split views supply the system sidebar material.
+                    // An additional glass surface changes its tint and contrast.
+                    if #unavailable(macOS 26.0) {
+                        LegacySidebarMaterialBackground()
+                            .ignoresSafeArea()
+                    }
+                }
+                .navigationSplitViewColumnWidth(
+                    min: Metrics.Sidebar.min,
+                    ideal: min(Metrics.Sidebar.ideal, sidebarMaxWidth),
+                    max: sidebarMaxWidth
+                )
         } detail: {
             detail
                 // Floating over the pane rather than docked under it, so switching

TFM/Design/DesignTokens.swift

@@ -444,24 +444,6 @@ private struct TermindGlassBar: ViewModifier {
     }
 }
 
-/// The Liquid Glass surface shared by every mode of the left column.
-///
-/// `NavigationSplitView` supplies the column geometry, but the custom AppKit
-/// lists inside it do not inherit SwiftUI's source-list background. Hosting one
-/// system glass surface behind the complete column keeps list rows and empty
-/// space on one coherent material, including behind the window titlebar.
-struct SidebarGlassBackground: View {
-    @ViewBuilder
-    var body: some View {
-        if #available(macOS 26.0, *) {
-            Color.clear
-                .glassEffect(.regular, in: .rect)
-        } else {
-            LegacySidebarMaterialBackground()
-        }
-    }
-}
-
 /// Native material fallback for systems before Liquid Glass.
 struct LegacySidebarMaterialBackground: NSViewRepresentable {
     func makeNSView(context: Context) -> NSVisualEffectView {