fix: keep the sidebar from sticking mid-slide when toggled quickly (INC-423)

Sources/ContentView.swift

@@ -731,6 +731,11 @@ struct ContentView: View {
                 updateSidebarResizerBandState()
                 syncTrafficLightInset()
             }
+            // The portal stops following SwiftUI frames when the slide ends; sync it to the final one.
+            .onReceive(NotificationCenter.default.publisher(for: .programaSidebarToggleDidSettle, object: sidebarState)) { _ in
+                guard let observedWindow else { return }
+                TerminalWindowPortalRegistry.scheduleExternalGeometrySynchronize(for: observedWindow)
+            }
             .onChange(of: sidebarMatchTerminalBackground) {
                 guard sidebarState.isVisible,
                       sidebarBlendMode == SidebarBlendModeOption.withinWindow.rawValue else { return }

Sources/Update/UpdateTitlebarAccessory.swift

@@ -743,6 +743,14 @@ private final class TrafficLightsTrailingEdgeView: NSView {
                 self?.scheduleMeasure()
             }
         }
+        // Measurements are skipped while the sidebar slides, so measure once it settles.
+        windowObservers.append(
+            NotificationCenter.default.addObserver(
+                forName: .programaSidebarToggleDidSettle, object: nil, queue: .main
+            ) { [weak self] _ in
+                self?.scheduleMeasure()
+            }
+        )
         scheduleMeasure()
     }
 
@@ -764,6 +772,8 @@ private final class TrafficLightsTrailingEdgeView: NSView {
         DispatchQueue.main.async { [weak self] in
             guard let self else { return }
             self.measurePending = false
+            // Mid-slide frames carry the transition offset; the settle notification re-measures.
+            guard !TerminalWindowPortalRegistry.isInteractiveGeometryResizeActive else { return }
             self.onChange?(self.measureZoomButtonMaxX())
         }
     }

Sources/VerticalTabsSidebar.swift

@@ -6,6 +6,9 @@ import SwiftUI
 extension Notification.Name {
     static let programaSidebarVisibilityDidChange =
         Notification.Name("programaSidebarVisibilityDidChange")
+    /// Posted with the `SidebarState` as object when its show/hide animation finishes.
+    static let programaSidebarToggleDidSettle =
+        Notification.Name("programaSidebarToggleDidSettle")
 }
 
 final class SidebarState: ObservableObject {
@@ -16,6 +19,17 @@ final class SidebarState: ObservableObject {
         }
     }
     @Published var persistedWidth: CGFloat
+    /// Slides whose completion has not run; released in deinit so a window closed
+    /// mid-slide cannot leave the global portal resize counter raised.
+    private var pendingSlides = 0
+
+    deinit {
+        let pending = pendingSlides
+        guard pending > 0 else { return }
+        Task { @MainActor in
+            for _ in 0..<pending { TerminalWindowPortalRegistry.endInteractiveGeometryResize() }
+        }
+    }
 
     init(isVisible: Bool = true, persistedWidth: CGFloat = CGFloat(SessionPersistencePolicy.defaultSidebarWidth)) {
         self.isVisible = isVisible
@@ -28,10 +42,19 @@ final class SidebarState: ObservableObject {
         // The terminal is an AppKit portal; marking the toggle as an interactive resize makes
         // it follow the animated SwiftUI frame every tick, as it does for a sidebar drag.
         TerminalWindowPortalRegistry.beginInteractiveGeometryResize()
-        withAnimation(reduceMotion ? .easeOut(duration: 0.15) : .snappy(duration: 0.24)) {
+        pendingSlides += 1
+        // `.removed` waits for the visual end: the default (logically complete) fires as soon as
+        // another toggle retargets the slide, which ended the portal resize mid-motion.
+        withAnimation(
+            reduceMotion ? .easeOut(duration: 0.15) : .snappy(duration: 0.24),
+            completionCriteria: .removed
+        ) {
             isVisible.toggle()
-        } completion: {
+        } completion: { [weak self] in
+            guard let self else { return }
+            self.pendingSlides -= 1
             TerminalWindowPortalRegistry.endInteractiveGeometryResize()
+            NotificationCenter.default.post(name: .programaSidebarToggleDidSettle, object: self)
         }
     }
 }