core: send selection_changed notification

The core had no signal to the apprt when the active selection changed,
so a consumer (e.g. a screen reader) kept reading a stale selection
until some unrelated query refreshed it.

This change adds a payload-less selection_changed action that's fired on
a selection state transition. The apprt reads the current selection
through the normal read path.

This consolidates selection state changes so the notification fires
consistently: all sites route through setSelection rather than calling
screen.select directly, including the mouse paths that previously
bypassed it for clipboard timing.

The new setSelectionAndCopy extends setSelection with the additional
'copy_on_select' behavior.

On macOS, this posts .ghosttySelectionDidChange, which is debounced
before posting a NSAccessibility .selectedTextChanged notification.

GTK has no consumer yet and no-ops the action.

macos/Sources/Ghostty/Ghostty.App.swift

@@ -620,6 +620,9 @@ extension Ghostty {
             case GHOSTTY_ACTION_RING_BELL:
                 ringBell(app, target: target)
 
+            case GHOSTTY_ACTION_SELECTION_CHANGED:
+                selectionChanged(app, target: target)
+
             case GHOSTTY_ACTION_READONLY:
                 setReadonly(app, target: target, v: action.action.readonly)
 
@@ -1070,6 +1073,27 @@ extension Ghostty {
             }
         }
 
+        private static func selectionChanged(
+            _ app: ghostty_app_t,
+            target: ghostty_target_s) {
+            switch target.tag {
+            case GHOSTTY_TARGET_APP:
+                Ghostty.logger.warning("selection changed does nothing with an app target")
+                return
+
+            case GHOSTTY_TARGET_SURFACE:
+                guard let surface = target.target.surface else { return }
+                guard let surfaceView = self.surfaceView(from: surface) else { return }
+                NotificationCenter.default.post(
+                    name: .ghosttySelectionDidChange,
+                    object: surfaceView
+                )
+
+            default:
+                assertionFailure()
+            }
+        }
+
         private static func setReadonly(
             _ app: ghostty_app_t,
             target: ghostty_target_s,

macos/Sources/Ghostty/GhosttyPackage.swift

@@ -360,6 +360,9 @@ extension Notification.Name {
     /// Ring the bell
     static let ghosttyBellDidRing = Notification.Name("com.mitchellh.ghostty.ghosttyBellDidRing")
 
+    /// The active selection changed
+    static let ghosttySelectionDidChange = Notification.Name("com.mitchellh.ghostty.ghosttySelectionDidChange")
+
     /// Readonly mode changed
     static let ghosttyDidChangeReadonly = Notification.Name("com.mitchellh.ghostty.didChangeReadonly")
     static let ReadonlyKey = ghosttyDidChangeReadonly.rawValue + ".readonly"

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

@@ -76,6 +76,9 @@ extension Ghostty {
         // Cancellable for search state needle changes
         private var searchNeedleCancellable: AnyCancellable?
 
+        // Cancellable for the debounced accessibility selection-change post.
+        private var accessibilitySelectionCancellable: AnyCancellable?
+
         // Whether the pointer should be visible or not
         @Published private(set) var pointerStyle: CursorStyle = .horizontalText
 
@@ -286,6 +289,16 @@ extension Ghostty {
                 }
             }
 
+            // A drag can emit multiple selection changes. Debounce so screen
+            // readers hear one announcement once the selection settles.
+            accessibilitySelectionCancellable = NotificationCenter.default
+                .publisher(for: .ghosttySelectionDidChange, object: self)
+                .debounce(for: .milliseconds(100), scheduler: DispatchQueue.main)
+                .sink { [weak self] _ in
+                    guard let self else { return }
+                    NSAccessibility.post(element: self, notification: .selectedTextChanged)
+                }
+
             // Before we initialize the surface we want to register our notifications
             // so there is no window where we can't receive them.
             let center = NotificationCenter.default