Self-heal off-screen main window instead of requiring quit/relaunch

macOS's built-in window-restore (Resume) can place the window at
coordinates for a display that's no longer connected, leaving it
visible-but-invisible with no way to recover short of quitting. Now
re-centers automatically on app activate/Dock reopen, plus a manual
"Reset Window Position" menu command as a guaranteed fallback.

oAI/oAIApp.swift

@@ -53,6 +53,41 @@ final class AppDelegate: NSObject, NSApplicationDelegate {
         return shouldTerminate ? .terminateNow : .terminateCancel
     }
 
+    // macOS's built-in window-restoration (Resume) can place the main window at coordinates
+    // that no longer correspond to any connected display (e.g. it was last positioned on an
+    // external monitor that's now disconnected). The window is still technically "visible"
+    // (isVisible == true), so clicking the Dock icon or Cmd+Tab-ing to the app doesn't trigger
+    // any of the usual recovery paths — the process runs fine, there's just nothing on screen.
+    // Self-heal by re-centering any main-sized window that doesn't intersect a current screen,
+    // both whenever the app becomes active and when the Dock icon is clicked with the app
+    // already running.
+    func applicationDidBecomeActive(_ notification: Notification) {
+        AppDelegate.repositionOffscreenWindows()
+    }
+
+    func applicationShouldHandleReopen(_ sender: NSApplication, hasVisibleWindows flag: Bool) -> Bool {
+        AppDelegate.repositionOffscreenWindows()
+        return true
+    }
+
+    /// Pure geometry check, kept separate from AppKit so it's directly testable.
+    nonisolated static func isFrameOffscreen(_ frame: CGRect, screenFrames: [CGRect]) -> Bool {
+        !screenFrames.contains { $0.intersects(frame) }
+    }
+
+    /// Re-centers the main window if it's off-screen, or unconditionally when `force` is true
+    /// (used by the manual "Reset Window Position" menu command).
+    static func repositionOffscreenWindows(force: Bool = false) {
+        let screenFrames = NSScreen.screens.map(\.frame)
+        for window in NSApp.windows where window.isVisible && !(window is NSPanel) && window.frame.width > 200 && window.frame.height > 200 {
+            if force || isFrameOffscreen(window.frame, screenFrames: screenFrames) {
+                window.center()
+            }
+            window.makeKeyAndOrderFront(nil)
+        }
+        NSApp.activate(ignoringOtherApps: true)
+    }
+
     // `chatViewModel` is wired from `ContentView.onAppear`, not from `oAIApp.init()` — reading
     // the `@State private var chatViewModel` there returns a throwaway instance distinct from
     // the one SwiftUI actually renders (confirmed via ObjectIdentifier logging: two different
@@ -217,6 +252,16 @@ struct oAIApp: App {
                     chatViewModel.onlineMode.toggle()
                 }
                 .keyboardShortcut("o", modifiers: [.command, .shift])
+
+                Divider()
+
+                // Fallback for when the window ends up off-screen (stale macOS window-restore
+                // coordinates, e.g. after an external monitor is disconnected) — see
+                // AppDelegate.repositionOffscreenWindows. No keyboard shortcut assigned yet;
+                // add one once it's been live-verified against macOS's reserved bindings.
+                Button("Reset Window Position") {
+                    AppDelegate.repositionOffscreenWindows(force: true)
+                }
             }
 
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