Fix pinned tab alignment with sidebar

Termind/App/RootView.swift

@@ -10,13 +10,19 @@ struct RootView: View {
     @Environment(\.colorScheme) private var colorScheme
     @State private var window: WindowModel
     @State private var hostsPageState = HostsPageState()
-    /// The last usable width reported by whichever sidebar is mounted.
+    /// The last usable leading edge reported by whichever detail column is mounted.
     ///
-    /// Keeping this at the window shell lets the pinned tabs track both the
-    /// Vault split view and the shared contextual sidebar. A hidden sidebar can
-    /// briefly report zero while it leaves the layout; that value is rejected
-    /// by `recordSidebarWidth` so the tab strip keeps the user's last width.
-    @State private var sidebarWidth = Metrics.Sidebar.ideal
+    /// The split view puts its native splitter outside the sidebar content, so
+    /// measuring that content stops short of the visual column boundary. The
+    /// detail column begins at the boundary the pinned tabs need to meet. A
+    /// hidden sidebar collapses that edge close to zero; measurements below the
+    /// split view's minimum sidebar width are rejected so the tab strip keeps
+    /// the user's last visible boundary.
+    @State private var pinnedTabStripWidth = Metrics.Sidebar.ideal
+
+    /// `nonisolated` because geometry transforms are `Sendable` closures and
+    /// this coordinate-space name is immutable, not main-actor state.
+    nonisolated private static let layoutSpace = "termind.rootLayout"
 
     init(window: WindowModel = WindowModel()) {
         _window = State(initialValue: window)
@@ -27,7 +33,7 @@ struct RootView: View {
         @Bindable var presentations = window.presentations
 
         VStack(spacing: 0) {
-            TabBarView(pinnedTabStripWidth: sidebarWidth)
+            TabBarView(pinnedTabStripWidth: pinnedTabStripWidth)
             Divider()
             splitContent
             if window.selectedTab != nil {
@@ -40,6 +46,7 @@ struct RootView: View {
             minHeight: Metrics.Window.minHeight,
             maxHeight: .infinity
         )
+        .coordinateSpace(.named(Self.layoutSpace))
         .toolbarBackground(WindowChrome.background(for: colorScheme), for: .windowToolbar)
         .toolbarBackground(.visible, for: .windowToolbar)
         // ⌘T and every Connect entry land here. A sheet rather than a page,
@@ -90,10 +97,15 @@ struct RootView: View {
             // Its detail owns the optional work split so showing New Host does
             // not reconstruct `VaultView` and discard an active query, selected
             // tags, scroll position, or search-field focus.
-            NavigationSplitView {
+            NavigationSplitView(columnVisibility: sidebarVisibility) {
                 vaultSidebar
             } detail: {
                 vaultWorkspace
+                    .onGeometryChange(for: CGFloat.self) {
+                        $0.frame(in: .named(Self.layoutSpace)).minX
+                    } action: {
+                        recordPinnedTabStripWidth($0)
+                    }
             }
             .navigationSplitViewStyle(.balanced)
         } else {
@@ -104,11 +116,6 @@ struct RootView: View {
                         ideal: Metrics.Sidebar.ideal,
                         max: Metrics.Sidebar.max
                     )
-                    .onGeometryChange(for: CGFloat.self) {
-                        $0.size.width
-                    } action: {
-                        recordSidebarWidth($0)
-                    }
             } detail: {
                 detail
                     .frame(
@@ -117,6 +124,11 @@ struct RootView: View {
                         minHeight: Metrics.Window.minHeight,
                         maxHeight: .infinity
                     )
+                    .onGeometryChange(for: CGFloat.self) {
+                        $0.frame(in: .named(Self.layoutSpace)).minX
+                    } action: {
+                        recordPinnedTabStripWidth($0)
+                    }
             }
             .navigationSplitViewStyle(.balanced)
         }
@@ -129,17 +141,14 @@ struct RootView: View {
                 ideal: Metrics.Sidebar.ideal,
                 max: Metrics.Sidebar.max
             )
-            .onGeometryChange(for: CGFloat.self) {
-                $0.size.width
-            } action: {
-                recordSidebarWidth($0)
-            }
     }
 
-    private func recordSidebarWidth(_ measuredWidth: CGFloat) {
-        sidebarWidth = PinnedTopLevelTabSizing.resolvedSidebarWidth(
-            current: sidebarWidth,
-            measured: measuredWidth
+    private func recordPinnedTabStripWidth(_ measuredDetailLeadingEdge: CGFloat) {
+        pinnedTabStripWidth = PinnedTopLevelTabSizing.resolvedStripWidth(
+            current: pinnedTabStripWidth,
+            measuredDetailLeadingEdge: measuredDetailLeadingEdge,
+            isSidebarVisible: window.showsSidebar,
+            minimumSidebarWidth: Metrics.Sidebar.min
         )
     }
 

Termind/Features/Tabs/PinnedTopLevelTabSizing.swift

@@ -4,15 +4,29 @@ import CoreGraphics
 nonisolated enum PinnedTopLevelTabSizing {
     private static let tabCount: CGFloat = 2
 
-    /// Divides the measured sidebar equally between the two pinned tabs.
-    static func tabWidth(sidebarWidth: CGFloat) -> CGFloat {
-        sidebarWidth / tabCount
+    /// Divides the strip ending at the sidebar's trailing edge equally between
+    /// the two pinned tabs.
+    static func tabWidth(stripWidth: CGFloat) -> CGFloat {
+        stripWidth / tabCount
     }
 
-    /// Ignores transient invalid measurements produced while a sidebar leaves
-    /// the split-view layout, preserving the last width for the pinned tabs.
-    static func resolvedSidebarWidth(current: CGFloat, measured: CGFloat) -> CGFloat {
-        guard measured.isFinite, measured > 0 else { return current }
-        return measured
+    /// Ignores invalid or collapsed detail-column edges produced while a
+    /// sidebar leaves the split-view layout, preserving the last strip width.
+    /// AppKit may leave the hidden edge at a hairline rather than exactly zero,
+    /// so validity is based on the split view's existing minimum sidebar width.
+    static func resolvedStripWidth(
+        current: CGFloat,
+        measuredDetailLeadingEdge: CGFloat,
+        isSidebarVisible: Bool,
+        minimumSidebarWidth: CGFloat
+    ) -> CGFloat {
+        guard
+            isSidebarVisible,
+            measuredDetailLeadingEdge.isFinite,
+            measuredDetailLeadingEdge >= minimumSidebarWidth
+        else {
+            return current
+        }
+        return measuredDetailLeadingEdge
     }
 }

Termind/Features/Tabs/TabBarView.swift

@@ -130,7 +130,7 @@ struct TabBarView: View {
     /// drop on this edge means the same thing as the first insertion slot.
     private var leadingStrip: some View {
         let pinnedTabWidth = PinnedTopLevelTabSizing.tabWidth(
-            sidebarWidth: pinnedTabStripWidth
+            stripWidth: pinnedTabStripWidth
         )
 
         return HStack(spacing: 0) {

TermindTests/PinnedTopLevelTabSizingTests.swift

@@ -10,35 +10,53 @@ struct PinnedTopLevelTabSizingTests {
         (Metrics.Sidebar.ideal, Metrics.Sidebar.ideal / 2),
         (Metrics.Sidebar.max, Metrics.Sidebar.max / 2),
     ])
-    func twoPinnedTabsSplitTheSidebarWidthEqually(
-        sidebarWidth: CGFloat,
+    func twoPinnedTabsSplitAtTheSidebarTrailingEdgeEqually(
+        stripWidth: CGFloat,
         expectedTabWidth: CGFloat
     ) {
-        let tabWidth = PinnedTopLevelTabSizing.tabWidth(sidebarWidth: sidebarWidth)
+        let tabWidth = PinnedTopLevelTabSizing.tabWidth(stripWidth: stripWidth)
 
         #expect(tabWidth == expectedTabWidth)
-        #expect(tabWidth * 2 == sidebarWidth)
+        #expect(tabWidth * 2 == stripWidth)
     }
 
-    @Test(arguments: [CGFloat.zero, -.infinity, .infinity, .nan])
-    func invalidMeasurementsPreserveTheLastSidebarWidth(measuredWidth: CGFloat) {
+    @Test(arguments: [CGFloat.zero, 1, Metrics.Sidebar.min - 1, -.infinity, .infinity, .nan])
+    func invalidOrCollapsedDetailLeadingEdgesPreserveTheLastStripWidth(
+        measuredDetailLeadingEdge: CGFloat
+    ) {
         let currentWidth = Metrics.Sidebar.ideal
 
         #expect(
-            PinnedTopLevelTabSizing.resolvedSidebarWidth(
+            PinnedTopLevelTabSizing.resolvedStripWidth(
                 current: currentWidth,
-                measured: measuredWidth
+                measuredDetailLeadingEdge: measuredDetailLeadingEdge,
+                isSidebarVisible: true,
+                minimumSidebarWidth: Metrics.Sidebar.min
             ) == currentWidth
         )
     }
 
     @Test
-    func positiveMeasurementReplacesThePreviousSidebarWidth() {
+    func positiveDetailLeadingEdgeReplacesThePreviousStripWidth() {
         #expect(
-            PinnedTopLevelTabSizing.resolvedSidebarWidth(
+            PinnedTopLevelTabSizing.resolvedStripWidth(
                 current: Metrics.Sidebar.ideal,
-                measured: Metrics.Sidebar.max
-            ) == Metrics.Sidebar.max
+                measuredDetailLeadingEdge: 270.5,
+                isSidebarVisible: true,
+                minimumSidebarWidth: Metrics.Sidebar.min
+            ) == 270.5
+        )
+    }
+
+    @Test
+    func visibleAnimationMeasurementsDoNotReplaceTheLastStripWidthAfterHiding() {
+        #expect(
+            PinnedTopLevelTabSizing.resolvedStripWidth(
+                current: 400.5,
+                measuredDetailLeadingEdge: 272,
+                isSidebarVisible: false,
+                minimumSidebarWidth: Metrics.Sidebar.min
+            ) == 400.5
         )
     }
 }