diff --git a/oAI/oAIApp.swift b/oAI/oAIApp.swift
index c9ce2f5..e72e5af 100644
--- a/oAI/oAIApp.swift
+++ b/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)
+                }
             }
 
             // ── Help menu ─────────────────────────────────────────────────
diff --git a/oAITests/WindowPositionTests.swift b/oAITests/WindowPositionTests.swift
new file mode 100644
index 0000000..2172030
--- /dev/null
+++ b/oAITests/WindowPositionTests.swift
@@ -0,0 +1,49 @@
+//
+//  WindowPositionTests.swift
+//  oAITests
+//
+// SPDX-License-Identifier: PolyForm-Noncommercial-1.0.0
+// Copyright (C) 2026 Rune Olsen
+
+import Testing
+import Foundation
+import CoreGraphics
+@testable import Confab
+
+@Suite("Off-screen window detection")
+struct WindowPositionTests {
+
+    private let mainScreen = CGRect(x: 0, y: 0, width: 2560, height: 1664)
+
+    @Test("Window inside the only connected screen is not off-screen")
+    func onscreenWindow() {
+        let frame = CGRect(x: 100, y: 100, width: 1024, height: 800)
+        #expect(AppDelegate.isFrameOffscreen(frame, screenFrames: [mainScreen]) == false)
+    }
+
+    @Test("Window at coordinates from a now-disconnected external display is off-screen")
+    func offscreenWindow() {
+        // e.g. previously positioned on an external monitor to the right of the built-in display
+        let frame = CGRect(x: 3000, y: 200, width: 1024, height: 800)
+        #expect(AppDelegate.isFrameOffscreen(frame, screenFrames: [mainScreen]) == true)
+    }
+
+    @Test("Window merely partially overlapping a screen counts as on-screen")
+    func partiallyOverlappingWindow() {
+        let frame = CGRect(x: 2500, y: 100, width: 1024, height: 800)
+        #expect(AppDelegate.isFrameOffscreen(frame, screenFrames: [mainScreen]) == false)
+    }
+
+    @Test("Off-screen relative to one display but onscreen on a second connected display")
+    func multiMonitorOnscreen() {
+        let secondScreen = CGRect(x: 2560, y: 0, width: 1920, height: 1080)
+        let frame = CGRect(x: 3000, y: 200, width: 1024, height: 800)
+        #expect(AppDelegate.isFrameOffscreen(frame, screenFrames: [mainScreen, secondScreen]) == false)
+    }
+
+    @Test("No connected screens means every window is off-screen")
+    func noScreens() {
+        let frame = CGRect(x: 100, y: 100, width: 1024, height: 800)
+        #expect(AppDelegate.isFrameOffscreen(frame, screenFrames: []) == true)
+    }
+}