Native Liquid Glass Tab Bar Request

Nucleic-Session: 11F2B35E-E813-4A5E-AD28-9173ECC0B789
Co-authored-by: Nucleic <[email protected]>

NucleicRemote/NucleicRemote/Views/AdaptiveRootView.swift

@@ -175,6 +175,10 @@ struct NucleicTabBar: View {
     @Binding var selection: Int
     /// Sessions blocking on a human — the red badge on the Sessions item (was the tab item badge).
     var needsYou: Int
+    @Environment(\.accessibilityReduceMotion) private var reduceMotion
+    /// Ties every item's selected-capsule to one shared geometry, so the "bubble" interpolates its
+    /// frame from the old tab to the new one instead of cross-fading — the native bar's slide.
+    @Namespace private var bubble
 
     private struct Item { let index: Int; let title: String; let icon: String }
     private let items = [
@@ -193,6 +197,10 @@ struct NucleicTabBar: View {
         .padding(.horizontal, 6)
         .padding(.vertical, 8)
         .glassBar()
+        // Drive the bubble's slide (and the label/tint crossfade) off the selection itself, so any
+        // change — tap here or a programmatic jump from a notification — springs across.
+        .animation(reduceMotion ? nil : .spring(response: 0.32, dampingFraction: 0.78),
+                   value: selection)
     }
 
     private func itemButton(_ item: Item) -> some View {
@@ -220,11 +228,14 @@ struct NucleicTabBar: View {
             .foregroundStyle(selected ? Palette.accent : Color.secondary)
             .frame(maxWidth: .infinity)
             .padding(.vertical, 4)
-            // The selected item rides a soft accent-tinted capsule, echoing the system floating
-            // bar's highlighted tab.
+            // The selected item rides a soft accent-tinted capsule that slides between tabs — only
+            // the selected item mounts it, and the shared `bubble` geometry makes the single capsule
+            // travel to the new tab, echoing the system floating bar's highlighted-tab indicator.
             .background {
                 if selected {
-                    Capsule().fill(Palette.accent.opacity(0.15))
+                    Capsule()
+                        .fill(Palette.accent.opacity(0.15))
+                        .matchedGeometryEffect(id: "selectionBubble", in: bubble)
                 }
             }
             .contentShape(Rectangle())