macos: goto_split direction is performable (#9284)

Fixes #9283

There was a comment here noting this deficiency. GTK implements this
properly.

macos/Sources/Features/Terminal/BaseTerminalController.swift

@@ -552,22 +552,11 @@ class BaseTerminalController: NSWindowController,
         guard let directionAny = notification.userInfo?[Ghostty.Notification.SplitDirectionKey] else { return }
         guard let direction = directionAny as? Ghostty.SplitFocusDirection else { return }
 
-        // Convert Ghostty.SplitFocusDirection to our SplitTree.FocusDirection
-        let focusDirection: SplitTree<Ghostty.SurfaceView>.FocusDirection
-        switch direction {
-        case .previous: focusDirection = .previous
-        case .next: focusDirection = .next
-        case .up: focusDirection = .spatial(.up)
-        case .down: focusDirection = .spatial(.down)
-        case .left: focusDirection = .spatial(.left)
-        case .right: focusDirection = .spatial(.right)
-        }
-
         // Find the node for the target surface
         guard let targetNode = surfaceTree.root?.node(view: target) else { return }
         
         // Find the next surface to focus
-        guard let nextSurface = surfaceTree.focusTarget(for: focusDirection, from: targetNode) else {
+        guard let nextSurface = surfaceTree.focusTarget(for: direction.toSplitTreeFocusDirection(), from: targetNode) else {
             return
         }
 

macos/Sources/Ghostty/Ghostty.App.swift

@@ -1025,26 +1025,38 @@ extension Ghostty {
                     guard let surfaceView = self.surfaceView(from: surface) else { return false }
                     guard let controller = surfaceView.window?.windowController as? BaseTerminalController else { return false }
 
-                    // For now, we return false if the window has no splits and we return
-                    // true if the window has ANY splits. This isn't strictly correct because
-                    // we should only be returning true if we actually performed the action,
-                    // but this handles the most common case of caring about goto_split performability
-                    // which is the no-split case.
+                    // If the window has no splits, the action is not performable
                     guard controller.surfaceTree.isSplit else { return false }
 
+                    // Convert the C API direction to our Swift type
+                    guard let splitDirection = SplitFocusDirection.from(direction: direction) else { return false }
+
+                    // Find the current node in the tree
+                    guard let targetNode = controller.surfaceTree.root?.node(view: surfaceView) else { return false }
+
+                    // Check if a split actually exists in the target direction before
+                    // returning true. This ensures performable keybinds only consume
+                    // the key event when we actually perform navigation.
+                    let focusDirection: SplitTree<Ghostty.SurfaceView>.FocusDirection = splitDirection.toSplitTreeFocusDirection()
+                    guard controller.surfaceTree.focusTarget(for: focusDirection, from: targetNode) != nil else {
+                        return false
+                    }
+
+                    // We have a valid target, post the notification to perform the navigation
                     NotificationCenter.default.post(
                         name: Notification.ghosttyFocusSplit,
                         object: surfaceView,
                         userInfo: [
-                            Notification.SplitDirectionKey: SplitFocusDirection.from(direction: direction) as Any,
+                            Notification.SplitDirectionKey: splitDirection as Any,
                         ]
                     )
 
+                    return true
+
                 default:
                     assertionFailure()
+                    return false
                 }
-
-                return true
         }
 
         private static func resizeSplit(

macos/Sources/Ghostty/Package.swift

@@ -223,7 +223,38 @@ extension Ghostty {
             }
         }
     }
+}
 
+#if canImport(AppKit)
+// MARK: SplitFocusDirection Extensions
+
+extension Ghostty.SplitFocusDirection {
+    /// Convert to a SplitTree.FocusDirection for the given ViewType.
+    func toSplitTreeFocusDirection<ViewType>() -> SplitTree<ViewType>.FocusDirection {
+        switch self {
+        case .previous:
+            return .previous
+
+        case .next:
+            return .next
+
+        case .up:
+            return .spatial(.up)
+
+        case .down:
+            return .spatial(.down)
+
+        case .left:
+            return .spatial(.left)
+
+        case .right:
+            return .spatial(.right)
+        }
+    }
+}
+#endif
+
+extension Ghostty {
     /// The type of a clipboard request
     enum ClipboardRequest {
         /// A direct paste of clipboard contents