Preserve recoverable windows in session snapshots

Sources/App/MainWindowController.swift

@@ -3,7 +3,7 @@ import CmuxWindowing
 
 @MainActor
 final class MainWindowController: ReleasingWindowController {
-    var onClose: (() -> Void)?
+    var onClose: ((NSWindow) -> Void)?
     var shouldClose: ((NSWindow) -> Bool)?
     var onFrameRestorationCheckpoint: ((NSWindow) -> Void)?
 
@@ -18,7 +18,7 @@ final class MainWindowController: ReleasingWindowController {
 #endif
 
     override func managedWindowWillClose(_ window: NSWindow) {
-        onClose?()
+        onClose?(window)
     }
 
     func windowDidExitFullScreen(_ notification: Notification) {

Sources/App/MainWindowVisibilityController.swift

@@ -141,6 +141,15 @@ final class MainWindowVisibilityController {
         committedClosedWindows.contains(window)
     }
 
+    /// Returns whether a hidden window was explicitly retained for a later
+    /// visibility restore. Generic `orderOut` calls do not enter this topology,
+    /// so stale ordered-out windows remain fail-closed for routing.
+    func participatesInRestoreTopology(_ window: NSWindow) -> Bool {
+        appHiddenWindowRestoreTargets.contains { $0 === window }
+            || dismissedWindowRestoreTargets.contains { $0 === window }
+            || pendingApplicationActivationKeyRestoreTarget === window
+    }
+
     @discardableResult
     func focus(
         _ window: NSWindow,