fix: linux, custom client, incoming only, resizable (#8005)

Signed-off-by: fufesou <shuanglongchen@yeah.net>

flutter/lib/common.dart

@@ -55,6 +55,12 @@ var isMobile = isAndroid || isIOS;
 var version = '';
 int androidVersion = 0;
 
+// Only used on Linux.
+// `windowManager.setResizable(false)` will reset the window size to the default size on Linux.
+// https://stackoverflow.com/questions/8193613/gtk-window-resize-disable-without-going-back-to-default
+// So we need to use this flag to enable/disable resizable.
+bool _linuxWindowResizable = true;
+
 /// only available for Windows target
 int windowsBuildNumber = 0;
 DesktopType? desktopType;
@@ -1572,7 +1578,7 @@ Future<void> saveWindowPosition(WindowType type, {int? windowId}) async {
       // `await windowManager.isMaximized()` will always return true
       // if is not resizable. The reason is unknown.
       //
-      // `windowManager.setResizable(!bind.isIncomingOnly());` in main.dart
+      // `setResizable(!bind.isIncomingOnly());` in main.dart
       isMaximized =
           bind.isIncomingOnly() ? false : await windowManager.isMaximized();
       position = await windowManager.getPosition();
@@ -3234,7 +3240,9 @@ Widget buildVirtualWindowFrame(BuildContext context, Widget child) {
   return Obx(
     () => Container(
       decoration: BoxDecoration(
-        color: isMainDesktopWindow ? Colors.transparent : Theme.of(context).colorScheme.background,
+        color: isMainDesktopWindow
+            ? Colors.transparent
+            : Theme.of(context).colorScheme.background,
         border: Border.all(
           color: Theme.of(context).dividerColor,
           width: stateGlobal.windowBorderWidth.value,
@@ -3258,4 +3266,18 @@ Widget buildVirtualWindowFrame(BuildContext context, Widget child) {
   );
 }
 
-get windowEdgeSize => isLinux && bind.isIncomingOnly() ? 0.0 : kWindowEdgeSize;
+get windowEdgeSize => isLinux && _linuxWindowResizable ? 0.0 : kWindowEdgeSize;
+
+// `windowManager.setResizable(false)` will reset the window size to the default size on Linux and then set unresizable.
+// See _linuxWindowResizable for more details.
+// So we use `setResizable()` instead of `windowManager.setResizable()`.
+//
+// We can only call `windowManager.setResizable(false)` if we need the default size on Linux.
+setResizable(bool resizable) {
+  if (isLinux) {
+    _linuxWindowResizable = resizable;
+    stateGlobal.refreshResizeEdgeSize();
+  } else {
+    windowManager.setResizable(resizable);
+  }
+}