fix(windows): restore keyboard focus when the cursor re-enters the remote image (rustdesk#15880)

* fix(windows): restore keyboard focus when the cursor re-enters the remote image

On Windows the raw key focus node is unfocused on window blur and nothing
requests it back, so returning to an already connected session left the
keyboard dead until the remote image was clicked.

Request focus from enterView(), gated on the window being active, the tab
being selected and no blocking overlay, so a background window cannot grab
system keys. enterOrLeave(true) is still driven by RawKeyFocusScope's
onFocusChange, so it is not called twice.

* fix(windows): refocus on window focus when the cursor already hovers the image

Alt+Tab or a taskbar click returns focus without a PointerEnter, so
enterView() cannot restore the keyboard. Reuse _cursorOverImage, gated
on the selected tab and no blocking overlay.

* refactor(windows): share one focus predicate for every requestFocus path

The relative-mouse-mode restore on window focus could hand remote input
to this page while a blocking dialog was up or the tab was not selected.

Author: palmoni5

flutter/lib/desktop/pages/remote_page.dart

@@ -273,6 +273,11 @@ class _RemotePageState extends State<RemotePage>
         tabState.tabs[selected].key == widget.id;
   }
 
+  // Every Windows requestFocus() must pass this, or a blocking dialog or an
+  // inactive tab could hand remote input to this page.
+  bool get _windowsCanFocusRemoteInput =>
+      _isSelectedTab && _blockableOverlayState.middleBlocked.isFalse;
+
   bool get _isMacOSKeyboardContextActive {
     return stateGlobal.isFocused.value && !_isWindowBlur && _isSelectedTab;
   }
@@ -513,6 +518,15 @@ class _RemotePageState extends State<RemotePage>
       _queueMacOSKeyboardAfterFullScreen(allowHiddenLifecycle: true);
     }
 
+    // Refocus without PointerEnter: the cursor already hovers the image when
+    // focus returns (Alt+Tab, taskbar), so enterView() never fires again.
+    if (isWindows &&
+        _cursorOverImage.value &&
+        _windowsCanFocusRemoteInput &&
+        !_rawKeyFocusNode.hasFocus) {
+      _rawKeyFocusNode.requestFocus();
+    }
+
     // Restore relative mouse mode constraints when window regains focus.
     if (_ffi.inputModel.relativeMouseMode.value) {
       if (isMacOS) {
@@ -523,7 +537,7 @@ class _RemotePageState extends State<RemotePage>
           _cursorOverImage.value = true;
           _macOSLocalFocusLost = false;
         }
-      } else {
+      } else if (!isWindows || _windowsCanFocusRemoteInput) {
         _rawKeyFocusNode.requestFocus();
       }
       _ffi.inputModel.onWindowFocus();
@@ -835,7 +849,16 @@ class _RemotePageState extends State<RemotePage>
       _macOSLocalFocusLost = false;
       stateGlobal.getInputSource(force: true);
       _syncMacOSKeyboardGrab(reassert: true, allowInactiveLifecycle: true);
-    } else if (!isWindows) {
+    } else if (isWindows) {
+      // Blur unfocuses this node and nothing restores it, so the keyboard stayed
+      // dead until a click. Focus only while the window is really active, or a
+      // background window would grab system keys. onFocusChange does enterOrLeave.
+      if (!_isWindowBlur &&
+          _windowsCanFocusRemoteInput &&
+          !_rawKeyFocusNode.hasFocus) {
+        _rawKeyFocusNode.requestFocus();
+      }
+    } else {
       if (!_rawKeyFocusNode.hasFocus) {
         _rawKeyFocusNode.requestFocus();
       }