Add an IsActiveTab assertion for integration tests

Side panel tabs share a window, so which tab is shown is decided by view
z-order rather than the visibility flag (every tab in a window is
'visible'). Tests had no way to assert which tab is actually drawn in
front, which is distinct from which view has keyboard focus. Expose the
window's top view and add an IsActiveTab assertion built on it.

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

pkg/gui/gui_driver.go

@@ -153,6 +153,12 @@ func (self *GuiDriver) View(viewName string) *gocui.View {
 	return view
 }
 
+// TopViewInWindow returns the frontmost visible view in the given window, i.e.
+// the tab that is currently shown when a window holds several tabbed views.
+func (self *GuiDriver) TopViewInWindow(windowName string) *gocui.View {
+	return self.gui.helpers.Window.TopViewInWindow(windowName, false)
+}
+
 func (self *GuiDriver) SetCaption(caption string) {
 	self.gui.setCaption(caption)
 	self.waitTillIdle()

pkg/integration/components/test_test.go

@@ -75,6 +75,10 @@ func (self *fakeGuiDriver) View(viewName string) *gocui.View {
 	return nil
 }
 
+func (self *fakeGuiDriver) TopViewInWindow(windowName string) *gocui.View {
+	return nil
+}
+
 func (self *fakeGuiDriver) SetCaption(string) {
 }
 

pkg/integration/components/view_driver.go

@@ -408,6 +408,28 @@ func (self *ViewDriver) IsFocused() *ViewDriver {
 	return self
 }
 
+// asserts that the view is the one currently shown in its window, i.e. it's the
+// active tab of its panel (drawn in front of the window's other tabs). Unlike
+// IsFocused, this is about what's displayed rather than which view has keyboard
+// focus; the two can disagree, e.g. if a config reload reshuffles the tabs.
+func (self *ViewDriver) IsActiveTab() *ViewDriver {
+	self.t.assertWithRetries(func() (bool, string) {
+		expected := self.getView().Name()
+		context := self.t.gui.ContextForView(expected)
+		if context == nil {
+			return false, fmt.Sprintf("%s: Could not find context for view, so can't determine its window", expected)
+		}
+		topView := self.t.gui.TopViewInWindow(context.GetWindowName())
+		actual := ""
+		if topView != nil {
+			actual = topView.Name()
+		}
+		return actual == expected, fmt.Sprintf("%s: Expected view to be the active tab of its window, but it was %s", expected, actual)
+	})
+
+	return self
+}
+
 func (self *ViewDriver) Press(key config.Keybinding) *ViewDriver {
 	self.IsFocused()
 

pkg/integration/types/types.go

@@ -44,6 +44,8 @@ type GuiDriver interface {
 	// e.g. when we're showing both staged and unstaged changes
 	SecondaryView() *gocui.View
 	View(viewName string) *gocui.View
+	// the frontmost visible view in the given window, i.e. the currently shown tab
+	TopViewInWindow(windowName string) *gocui.View
 	SetCaption(caption string)
 	SetCaptionPrefix(prefix string)
 	// Pop the next toast that was displayed; returns nil if there was none