macos: auto-expire cached screen contents

macos/Sources/Ghostty/SurfaceView_AppKit.swift

@@ -1926,39 +1926,43 @@ extension Ghostty.SurfaceView {
 /// Caches a value for some period of time, evicting it automatically when that time expires.
 /// We use this to cache our surface content. This probably should be extracted some day
 /// to a more generic helper.
-///
-// TODO:
-// - Auto-expire the data so it doesn't take memory
 fileprivate class CachedValue<T> {
-    private var value: Value?
+    private var value: T?
     private let fetch: () -> T
     private let duration: Duration
-
-    struct Value {
-        var value: T
-        var expires: ContinuousClock.Instant
-    }
+    private var expiryTask: Task<Void, Never>?
 
     init(duration: Duration, fetch: @escaping () -> T) {
         self.duration = duration
         self.fetch = fetch
     }
 
-    func get() -> T {
-        let now = ContinuousClock.now
-        if let value {
-            // If the value isn't expired just return it
-            if value.expires > now {
-                return value.value
-            }
+    deinit {
+        expiryTask?.cancel()
+    }
 
-            // Value is expired, clear it
-            self.value = nil
+    func get() -> T {
+        if let value {
+            return value
         }
 
         // We don't have a value (or it expired). Fetch and store.
         let result = fetch()
-        self.value = .init(value: result, expires: now + duration)
+        let now = ContinuousClock.now
+        let expires = now + duration
+        self.value = result
+
+        // Schedule a task to clear the value
+        expiryTask = Task { [weak self] in
+            do {
+                try await Task.sleep(until: expires)
+                self?.value = nil
+                self?.expiryTask = nil
+            } catch {
+                // Task was cancelled, do nothing
+            }
+        }
+
         return result
     }
 }