fix(flutter): make Adjust Window reliable across desktop platforms (#15853)

* fix(flutter): make Adjust Window reliable across desktop platforms

  - Fix incorrect sizing on scaled displays by calculating the target from the
    rendered canvas scale and platform-specific window coordinate units.
  - Fix adjustments using the wrong monitor by querying the current remote
    window's screen, with the main window as fallback.
  - Fix stale geometry after fullscreen or maximized transitions by refreshing
    metrics before calculating and applying the target frame.
  - Fix fullscreen availability checks on Windows and macOS by predicting the
    restored window borders and caching each macOS window's pre-fullscreen work area.
  - Fix incorrect Linux work areas by handling GNOME Wayland fractional scaling
    and caching compositor/X11 work-area measurements when visibleFrame is wrong.
  - Prevent unsafe adjustments by rejecting invalid, oversized, or implausibly
    small target frames.
  - Avoid failures during window teardown by skipping adjustment when the view,
    screen, or native window frame is unavailable.

Signed-off-by: 21pages <sunboeasy@gmail.com>

* fix(flutter): harden Adjust Window handling

  - Use the dynamic Linux resize edge when predicting restored window bounds.
  - Treat GNOME fractional-scaling lookup failures as unknown without repeating
    the lookup for the remote window.
  - Stop adjustment safely when native window calls fail during window teardown.

Signed-off-by: 21pages <sunboeasy@gmail.com>

* fix(flutter): correct Linux monitor selection

Update window_size to use monitor height for vertical bounds, preventing incorrect screen selection with vertically stacked displays.

Signed-off-by: 21pages <sunboeasy@gmail.com>

* docs(flutter): simplify Linux screen handling comments

Keep the source rationale concise and move platform measurements and investigation details out of the implementation.

Signed-off-by: 21pages <sunboeasy@gmail.com>

* fix(flutter): align Adjust Window resize padding

Use the shared drag-to-resize padding for Linux restored-window predictions so menu validation matches the applied frame dimensions.

Signed-off-by: 21pages <sunboeasy@gmail.com>

* fix(flutter): remove Adjust Window screen fallback

Return null when the current window screen is unavailable instead of using the main window's scale factor and work area.

Signed-off-by: 21pages <sunboeasy@gmail.com>

* fix(linux): query Mutter monitor layout mode

  Use DisplayConfig.GetCurrentState instead of inferring scaling from
  experimental features, and handle Ubuntu's UI-scaled logical mode.

Signed-off-by: 21pages <sunboeasy@gmail.com>

* fix(flutter): use native maximized state for Wayland cache

Signed-off-by: 21pages <sunboeasy@gmail.com>

* fix(flutter): allow Adjust Window to fill work area

Signed-off-by: 21pages <sunboeasy@gmail.com>

* fix(flutter): avoid racing screen info updates

Signed-off-by: 21pages <sunboeasy@gmail.com>

* refactor(flutter): remove dead Adjust Window web plumbing

Signed-off-by: 21pages <sunboeasy@gmail.com>

* fix(flutter): tolerate near-unity Wayland scale factors

Signed-off-by: 21pages <sunboeasy@gmail.com>

* fix(flutter): harden window screen detection

Signed-off-by: 21pages <sunboeasy@gmail.com>

* fix(linux): drop deprecated GNOME session detection

Signed-off-by: 21pages <sunboeasy@gmail.com>

* fix(flutter): remove GNOME monitor layout mode flutter cache

Signed-off-by: 21pages <sunboeasy@gmail.com>

---------

Signed-off-by: 21pages <sunboeasy@gmail.com>

flutter/macos/Runner/MainFlutterWindow.swift

@@ -36,8 +36,28 @@ class RelativeMouseState {
 }
 
 class MainFlutterWindow: NSWindow {
+    private static let fullscreenWorkAreaSizes = NSMapTable<NSWindow, NSValue>(
+        keyOptions: [.weakMemory, .objectPointerPersonality],
+        valueOptions: .strongMemory
+    )
+    private static let fullscreenObserver = NotificationCenter.default.addObserver(
+        forName: NSWindow.willEnterFullScreenNotification,
+        object: nil,
+        queue: .main
+    ) { notification in
+        guard let window = notification.object as? NSWindow,
+              let screen = window.screen else {
+            return
+        }
+        fullscreenWorkAreaSizes.setObject(
+            NSValue(size: screen.visibleFrame.size),
+            forKey: window
+        )
+    }
+
     override func awakeFromNib() {
         rustdesk_core_main();
+        _ = MainFlutterWindow.fullscreenObserver
         let flutterViewController = FlutterViewController.init()
         let windowFrame = self.frame
         self.contentViewController = flutterViewController
@@ -278,6 +298,16 @@ class MainFlutterWindow: NSWindow {
                     self.disableNativeRelativeMouseMode()
                     result(true)
 
+                case "getMacOSWorkAreaSize":
+                    guard Thread.isMainThread,
+                          let window = registrar.view?.window,
+                          let size = MainFlutterWindow.fullscreenWorkAreaSizes
+                            .object(forKey: window)?.sizeValue else {
+                        result(nil)
+                        break
+                    }
+                    result([Double(size.width), Double(size.height)])
+
                 default:
                     result(FlutterMethodNotImplemented)
                 }