macos: only show split grab handle when the mouse is near it (#11383)

Fixes #11379

For this pass, I made it a very simple "within 20%" (height-wise) of the
split handle down. There is no horizontal component. I want to find the
right balance between always visible (today mostly) to only visible on
direct hover, because I think it'll be too hard to discover on that far
right side.

macos/Sources/Ghostty/Surface View/SurfaceGrabHandle.swift

@@ -3,6 +3,12 @@ import SwiftUI
 extension Ghostty {
     /// A grab handle overlay at the top of the surface for dragging a surface.
     struct SurfaceGrabHandle: View {
+        // Size of the actual drag handle; the hover reveal region is larger.
+        private static let handleSize = CGSize(width: 80, height: 12)
+
+        // Reveal the handle anywhere within the top % of the pane height.
+        private static let hoverHeightFactor: CGFloat = 0.2
+
         @ObservedObject var surfaceView: SurfaceView
 
         @State private var isHovering: Bool = false
@@ -19,7 +25,15 @@ extension Ghostty {
         }
 
         private var ellipsisVisible: Bool {
-            surfaceView.mouseOverSurface && surfaceView.cursorVisible
+            // If the cursor isn't visible, never show the handle
+            guard surfaceView.cursorVisible else { return false }
+            // If we're hovering or actively dragging, always visible
+            if isHovering || isDragging { return true }
+
+            // Require our mouse location to be within the top area of the
+            // surface.
+            guard let mouseLocation = surfaceView.mouseLocationInSurface else { return false }
+            return Self.isInHoverRegion(mouseLocation, in: surfaceView.bounds)
         }
 
         var body: some View {
@@ -30,7 +44,7 @@ extension Ghostty {
                         isDragging: $isDragging,
                         isHovering: $isHovering
                     )
-                    .frame(width: 80, height: 12)
+                    .frame(width: Self.handleSize.width, height: Self.handleSize.height)
                     .contentShape(Rectangle())
 
                     if ellipsisVisible {
@@ -45,5 +59,23 @@ extension Ghostty {
                 .frame(maxWidth: .infinity, maxHeight: .infinity, alignment: .top)
             }
         }
+
+        /// The full-width hover band that reveals the drag handle.
+        private static func hoverRect(in bounds: CGRect) -> CGRect {
+            guard !bounds.isEmpty else { return .zero }
+
+            let hoverHeight = min(bounds.height, max(handleSize.height, bounds.height * hoverHeightFactor))
+            return CGRect(
+                x: bounds.minX,
+                y: bounds.maxY - hoverHeight,
+                width: bounds.width,
+                height: hoverHeight
+            )
+        }
+
+        /// Returns true when the pointer is inside the top hover band.
+        private static func isInHoverRegion(_ point: CGPoint, in bounds: CGRect) -> Bool {
+            hoverRect(in: bounds).contains(point)
+        }
     }
 }

macos/Sources/Ghostty/Surface View/SurfaceView_AppKit.swift

@@ -119,6 +119,10 @@ extension Ghostty {
         // Whether the mouse is currently over this surface
         @Published private(set) var mouseOverSurface: Bool = false
 
+        // The last known mouse location in the surface's local coordinate space,
+        // used by overlays such as the split drag handle reveal region.
+        @Published private(set) var mouseLocationInSurface: CGPoint?
+
         // Whether the cursor is currently visible (not hidden by typing, etc.)
         @Published private(set) var cursorVisible: Bool = true
 
@@ -952,13 +956,15 @@ extension Ghostty {
             mouseOverSurface = true
             super.mouseEntered(with: event)
 
+            let pos = self.convert(event.locationInWindow, from: nil)
+            mouseLocationInSurface = pos
+
             guard let surfaceModel else { return }
 
             // On mouse enter we need to reset our cursor position. This is
             // super important because we set it to -1/-1 on mouseExit and
             // lots of mouse logic (i.e. whether to send mouse reports) depend
             // on the position being in the viewport if it is.
-            let pos = self.convert(event.locationInWindow, from: nil)
             let mouseEvent = Ghostty.Input.MousePosEvent(
                 x: pos.x,
                 y: frame.height - pos.y,
@@ -969,6 +975,7 @@ extension Ghostty {
 
         override func mouseExited(with event: NSEvent) {
             mouseOverSurface = false
+            mouseLocationInSurface = nil
             guard let surfaceModel else { return }
 
             // If the mouse is being dragged then we don't have to emit
@@ -988,10 +995,12 @@ extension Ghostty {
         }
 
         override func mouseMoved(with event: NSEvent) {
+            let pos = self.convert(event.locationInWindow, from: nil)
+            mouseLocationInSurface = pos
+
             guard let surfaceModel else { return }
 
             // Convert window position to view position. Note (0, 0) is bottom left.
-            let pos = self.convert(event.locationInWindow, from: nil)
             let mouseEvent = Ghostty.Input.MousePosEvent(
                 x: pos.x,
                 y: frame.height - pos.y,